ENGINE DIAGNOSTIC

Diagnose Start Engine Push Button

Most newer vehicles have replaced the traditional key-style ignition switch with a Start Engine Push button system. A Smart Fob sends a coded security signal to the Powertrain Control Module (PCM) via the vehicle's keyless entry system when the fob is inside the vehicle. This tells the PCM that the engine can be started at any time.
Before the engine will start, the transmission must be in Park or Neutral, and the driver must depress and hold the brake pedal. Pressing the Start Engine Button sends a command to the PCM. The PCM then checks the status of the Park/Neutral Safety switch and the Brake Pedal Switch. If the transmission is in Park or Neutral, and the brake is on, the PCM then sends a start command to the starter motor to crank the engine.

NOTHING HAPPENS WHEN YOU PRESS THE START ENGINE BUTTON

If the engine does not crank when you press the Start Engine button, any of the following may be preventing the engine from starting:

Dead battery inside Smart Key Fob
What to do: Hold the dead key fob against the start button, then use the fob to press the Start Engine button down. This should allow the button to inductively read the security code in the fob and pass the start command to the PCM. Your engine should start.

Replace the dead battery inside the Smart Fob with a new battery as soon as possible.

Wrong Key Fob or Defective Key Fob
If you accidentally picked up the wrong key fob for your vehicle, or the fob itself is defective, your engine will NOT start.
What To Do: Have your vehicle towed to your car dealer to have a new fob programmed for your vehicle, or call a certified locksmith who can replace and program a new key fob.

Defective Start Engine Button
You have the correct key fob and the battery inside the fob is good, but nothing happens when you press the Start Engine Button or use the fob to press the Start Button.
What To Do: Replace the defective Start Engine Button with a new one.

Car Battery is Dead
A dead or discharged car battery can prevent your engine from cranking or starting.
What To Do: Open the hood and check battery voltage with a volt meter. A battery that has more than about 12.4 volts should have enough voltage to start your engine. If the battery is low or dead, try jump starting the battery from another vehicle, or hook up a battery charger to recharge or boost the battery. Also, check the battery cable connections to make sure they are clean and tight. Have your battery tested to determine its condition. If it is more than 4 or 5 years old, chances are you need a new battery.

PCM Problem
If the PCM has an internal fault, or there is a problem with the anti-theft system (such as not reading the fob correctly or the security codes have gotten out of sync), further diagnosis will be necessary to determine the problem. There may a programming issue, or a fault in the keyless entry system or keyless entry module that routes the security signal to the PCM.
What To Do: This type of diagnosis is beyond the skill level of most do-it-yourselfers and requires a professional grade scan tool with bi-directional and reprogramming capability.

Bad Starter
If the starter motor, or the relay, module or solenoid that energizes the starter is bad, the starter will not crank the engine.
What To Do: Try jumping the starter directly to see if it cranks the engine. This will tell you if the starter is working. The starter can also be removed and taken to an auto parts store that has a starter tester. If the starter tests bad, you need a new starter. If it tests good, the problem is not the start but likely a bad starter module, relay or solenoid. Be sure to inspect all the cables and wires that connects to the starter. Loose, corroded or damaged wire connections can prevent a good starter from cranking. So can a low battery.
Also, a damaged starter drive gear or missing or broken teeth on the engine's flywheel may prevent the starter from cranking the engine.

Blown Fuse
What To Do: Locate the Power Center under the hood and check for blown fuses in the starter circuit. Replace as needed (always replace with same amp capacity fuse).

Engine Cranks But Will Not Start

The problem is NOT the Start Engine Push Button but something else that is preventing the engine from getting spark, fuel or compression. This will require further diagnosis to determine the fault. Most likely causes are:
Dead Fuel Pump (or bad fuel pump relay)

Fuel Tank Empty (or fuel contaminated with water)

Bad Crank Position Sensor

Broken Timing Belt (no Compression)
 

Engine Won't Crank or Start

What To Do When Your Car Won't Start

Every engine requires four basic ingredients to start: sufficient cranking speed, good compression, adequate ignition voltage (with correct timing) and fuel (a relatively rich air/fuel mixture initially). So if your car fails to start, you can assume it lacks one of these four essential ingredients. But which one?
To find you, you need to analyze the situation. If the engine won't crank, you are probably dealing with a starter or battery problem. Has the starter been acting up? (unusual noises, slow cranking, etc.). Is this the first time the engine has failed to crank or start, or has it happened before? Have the starter, battery or battery cables been replaced recently? Might be a defective part. Has the battery been running down? Might be a charging problem. Have there been any other electrical problems?

If an engine cranks but refuses to start, it lacks ignition, fuel or compression. Was it running fine but quit suddenly? The most likely causes here would be a failed fuel pump, ignition module or broken overhead cam timing belt. Has the engine been getting progressively harder to start? If yes, consider the engine's maintenance and repair history.

NO START DIAGNOSIS

What happens when you attempt to start the engine? If nothing happens when you turn the key, check the battery to determine its state of charge. Many starters won't do a thing unless there is at least 10 volts available from the battery. A low battery does not necessarily mean the battery is the problem, though. The battery may have been run down by prolonged cranking while trying to start the engine. Or, the battery's low state of charge may be the result of a charging system problem. Either way, the battery needs to be recharged and tested.
If the battery is low, the next logical step might be to try starting the engine with another battery or a charger. If the engine cranks normally and roars to life, you can assume the problem was a dead battery, or a charging problem that allowed the battery to run down. If the battery accepts a charge and tests okay, checking the output of the charging system should help you identify any problems there.
A charging that is working properly should produce a charging voltage of somewhere around 14 volts at idle with the lights and accessories off. When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage. The exact charging voltage will vary according to the battery's state of charge, the load on the electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage. The charging range for a typical alternator might be 13.9 to 14.4 volts at 80 degrees F, but increase to 14.9 to 15.8 volts at subzero temperatures.
If the charging system is not putting out the required voltage, is it the alternator or the regulator? Full fielding the alternator to bypass the regulator should tell you if it is working correctly. Or, take the alternator to a parts store and have it bench tested. If the charging voltage goes up when the regulator is bypassed, the problem is the regulator (or the engine computer in the case of computer-regulated systems). If there is no change in output voltage, the alternator is the culprit.
Many times one or more diodes in the alternator rectifier assembly will have failed, causing a drop in the unit's output. The alternator will still produce current, but not enough to keep the battery fully charged. This type of failure will show up on an oscilloscope as one or more missing humps in the alternator waveform. Most charging system analyzers can detect this type of problem.

ENGINE CRANKING PROBLEMS

If your car won't start because the engine won't crank or cranks slowly (and the battery is fully charged), you can focus your attention on the starter circuit. A quick way to diagnose cranking problems is to switch on the headlights and watch what happens when you attempt to start the engine. If the headlights go out, a poor battery cable connection may be strangling the flow of amps. All battery cable connections should be checked and cleaned along with the engine-to-chassis ground straps.
Measuring the voltage drop across connections is a good way to find excessive resistance. A voltmeter check of the cable connections should show no more than 0.1 volt drop at any point, and no more than 0.4 volts for the entire starter circuit. A higher voltage drop would indicate excessive resistance and a need for cleaning or tightening.
Slow cranking can also be caused by undersized battery cables. Some cheap replacement cables have small gauge wire encased in thick insulation. The cables look the same size as the originals on the outside, but inside there is not enough wire to handle the amps.

If the headlights continue to shine brightly when you attempt to start the engine and nothing happens (no cranking), voltage is not reaching the starter. The problem here is likely an open or misadjusted park/neutral safety switch, a bad ignition switch a bad start engine push button or a faulty starter relay or solenoid. Fuses and fusible links should also be checked because overloads caused by continuous cranking or jump starting may have blown one of these protective devices

If the starter or solenoid clicks but nothing else happens when you attempt to start the engine, there may not be enough amps to spin the starter. Or the starter  may be bad. A poor battery cable, solenoid or ground connection, or high resistance in the solenoid itself may be the problem. A voltage check at the solenoid will reveal if battery voltage is passing through the ignition switch circuit. If the solenoid or relay is receiving battery voltage but is not closing or passing enough amps from the battery to spin the starter motor, the solenoid ground may be bad or the contacts in the solenoid may be worn, pitted or corroded. If the starter cranks when the solenoid is bypassed, a new solenoid is needed, not a starter.
Most engines need a cranking speed of 200 to 300 rpm for your car to start, so if the starter is weak and can't crank the engine fast enough to build compression, the engine won't start. In some instances, a weak starter may crank the engine fast enough but prevent it from starting because it draws all the power from the battery and does not leave enough for the injectors or ignition system.
If the lights dim and there is little or no cranking when you attempt to start the engine, the starter may be locked up, dragging or suffering from high internal resistance, worn brushes, shorts or opens in the windings or armature. A starter current draw test will tell you if the starter is pulling too many amps.
A good starter will normally draw 60 to 150 amps with no load on it, and up to 200 amps or more while cranking the engine. The no load amp draw depends on the rating of the starter while the cranking amp draw depends on the displacement and compression of the engine. Always refer to the OEM specs for the exact amp values. Some "high torque" GM starters, for example, may have a no load draw of up to 250 amps. Toyota starters on four-cylinder engines typically draw 130 to 150 amps, and up to 175 amps on six-cylinder engines.
An unusually high current draw and low free turning speed or cranking speed typically indicates a shorted armature, grounded armature or field coils, or excessive friction within the starter itself (dirty, worn or binding bearings or bushings, a bent armature shaft or contact between the armature and field coils). The magnets in permanent magnet starters can sometimes break or separate from the housing and drag against the armature.
A starter that does not turn at all and draws a high current may have a ground in the terminal or field coils, or a frozen armature. On the other hand, the start may be fine but can't crank the engine because the engine is seized or hydrolocked. So before you condemn the starter, try turning the engine over by hand. Won't budge? Then the engine is probably locked up.
A starter that won't spin at all and draws zero amps has an open field circuit, open armature coils, defective brushes or a defective solenoid. Low free turning speed combined with a low current draw indicates high internal resistance (bad connections, bad brushes, open field coils or armature windings).
If the starter motor spins but fails to engage the flywheel, the cause may be a weak solenoid, defective starter drive or broken teeth on the flywheel. A starter drive that is on the verge of failure may engage briefly but then slip. Pull the starter and inspect the drive. It should turn freely in one direction but not in the other. A bad drive will turn freely in both directions or not at all.

ENGINE CRANKS BUT YOUR CAR WILL NOT START

When the engine cranks normally but you car won't start, you need to check ignition, fuel and compression. Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup.
A tool such as an Ignition System Simulator can speed the diagnosis by quickly telling you if the ignition module and coil are capable of producing a spark with a simulated timing input signal. If the simulated signal generates a spark, the problem is a bad distributor pickup or crankshaft position sensor. No spark would point to a bad module or coil. Measuring ignition coil primary and secondary resistance can rule out that component as the culprit.
Module problems as well as pickup problems are often caused by loose, broken or corroded wiring terminals and connectors. Older GM HEI ignition modules are notorious for this. If you are working on a distributorless ignition system with a Hall effect crankshaft position sensor, check the sensor's reference voltage (VRef) and ground. The sensor must have 5 volts or it will remain permanently off and not generate a crank signal (which should set a fault code). Measure VRef between the sensor power supply wire and ground (use the engine block for a ground, not the sensor ground circuit wire). Don't see 5 volts? Then check the sensor wiring harness for loose or corroded connectors. A poor ground connection will have the same effect on the sensor operation as a bad VRef supply. Measure the voltage drop between the sensor ground wire and the engine block. More than a 0.1 voltage drop indicates a bad ground connection. Check the sensor mounting and wiring harness.
If a Hall effect crank sensor has power and ground, the next thing to check would be its output. With nothing in the sensor window, the sensor should be "on" and read 5 volts (VRef). Measure the sensor D.C. output voltage between the sensor signal output wire and ground (use the engine block again, not the ground wire). When the engine is cranked, the sensor output should drop to zero every time the shutter blade, notch, magnetic button or gear tooth passes through the sensor. No change in voltage would indicate a bad sensor that needs to be replaced.
If the primary side of the ignition system seems to be producing a trigger signal for the coil but the voltage is not reaching the plugs, a visual inspection of the coil tower, distributor cap, rotor and plug wires should be made to identify any defects that might be preventing the spark from reaching its intended destination.

ENGINE CRANKS, HAS SPARK BUT WILL NOT START

If you see a good hot spark when you crank the engine, but it won't start, check for fuel. The problem might be a bad fuel pump.
On an older engine with a carburetor, pump the throttle linkage and look for fuel squirting into the carburetor throat. No fuel? Possible causes include a bad mechanic fuel pump, stuck needle valve in the carburetor, a plugged fuel line or fuel filter.
On newer vehicles with electronic fuel injection, connect a pressure gauge to the fuel rail to see if there is any pressure in the line. No pressure when the key is on? Check for a failed fuel pump, pump relay, fuse or wiring problem. On Fords, don't forget to check the inertia safety switch which is usually hidden in the trunk or under a rear kick panel. The switch shuts off the fuel pump in an accident. So if the switch has been tripped, resetting it should restore the flow of fuel to the engine. Lack of fuel can also be caused by obstructions in the fuel line or pickup sock inside the tank. And don't forget to check the fuel gauge. It is amazing how many no starts are caused by an empty fuel tank.
There is also the possibility that the fuel in the tank may be heavily contaminated with water or overloaded with alcohol. If the tank was just filled, bad gas might be causing the problem.
On EFI-equipped engines, fuel pressure in the line does not necessarily mean the fuel is being injected into the engine. Listen for clicking or buzzing that would indicate the injectors are working. No noise? Check for voltage and ground at the injectors. A defective ECM may not be driving the injectors, or the EFI power supply relay may have called it quits. Some EFI-systems rely on input from the camshaft position sensor to generate the injector pulses. Loss of this signal could prevent the system from functioning.
Even if there is fuel and it is being delivered to the engine, a massive vacuum leak could be preventing the engine from starting. A large enough vacuum leak will lean out the air/fuel ratio to such an extent that the mixture won't ignite. An EGR valve that is stuck wide open, a disconnected PCV hose, loose vacuum hose for the power brake booster, or similar leak could be the culprit. Check all vacuum connections and listen for unusual sucking noises while cranking.

ENGINE HAS FUEL AND SPARK BUT WILL NOT START

An engine that has fuel and spark, no serious vacuum leaks and cranks normally should start. The problem is compression . If it is an overhead cam engine with a rubber timing belt, a broken timing belt would be the most likely cause especially if the engine has a lot of miles on it. Most OEMs recommend replacing the OHC timing belt every 60,000 miles for preventative maintenance, but many belts are never changed. Eventually they break, and when they do the engine stops dead in its tracks. And in engines that lack sufficient valve-to-piston clearance as many import engines and some domestic engines do, it also causes extensive damage (bent valves and valvetrain components & sometimes cracked pistons).
Overhead cams can also bind and break if the head warps due to severe overheating, or the cam bearings are starved for lubrication. A cam seizure may occur during a subzero cold start if the oil in the crankcase is too thick and is slow to reach the cam (a good reason for using 5W-20 or 5W-30 for winter driving). High rpm cam failure can occur if the oil level is low or the oil is long overdue for a change.
With high mileage pushrod engines, the timing chain may have broken or slipped. Either type of problem can be diagnosed by doing a compression check and/or removing a valve cover and watching for valve movement when the engine is cranked.
A blown head gasket may prevent an engine from starting if the engine is a four cylinder with two dead cylinders. But most six or eight cylinder engines will sputter to life and run roughly even with a blown gasket. The gasket can, however, allow coolant to leak into the cylinder and hydrolock the engine.

Diagnose Engine Noise

Engine noise is usually a symptom that something may be wrong with your motor. All engines make some operating noise, but when you hear an unusual noise or excessive noise coming from under the hood, it usually means trouble. Here are some common engine noises and their possible causes:

ENGINE CLICKING NOISES

A clicking or tapping noise that gets louder when you rev the engine is probably "tappet" or upper valvetrain noise caused by one of several things: low oil pressure, excessive valve lash, or worn or damaged parts.
First, check the engine dipstick to see if the oil level is low. If low, add oil to bring it back up to the full mark. Is the engine still noisy? Check your oil pressure. A low gauge reading (or oil warning light) would indicate a serious internal engine problem that is preventing normal oil pressure from reaching the upper valve train components. The cause might be a worn or damaged oil pump, a clogged oil pump pickup screen or a plugged up oil filter Using too thick a viscosity of motor oil during cold weather can also slow down the flow of oil to the upper valvetrain, causing noise and wear.

COLLAPSED LIFTER NOISE

Worn, leaky or dirty lifters can also cause valvetrain noise. If oil delivery is restricted to the lifters (plugged oil galley or low oil pressure), the lifters won't "pump up" to take up the normal slack in the valvetrain. A "collapsed" lifter will then allow excessive valve lash and noise.

ENGINE VALVE NOISE

If you can rule out lubrication-related problems as a cause, the next step would be to remove the valve cover(s) and check valve lash. On older import engines, mechanical lifters require periodic valve lash adjustments (typically every 30,000 miles). Too much space between the tips of the rocker arms and valve stems can make the valvetrain noisy -- and possibly cause accelerated wear of both parts.
To measure (and adjust valve lash, you need a feeler gauge. The gauge is slid between the tip of the valve stem and rocker arm (or the cam follower or the cam itself on overhead cam engines) when the piston is at top dead center (valve fully closed). Refer to a manual for the specified lash and adjustment procedure. Also, note whether the lash spec is for a hot or cold engine (this makes a big difference!).
On engines with hydraulic lifters, oil pressure pumps up the lifters when the engine is running to maintain zero lash in the valvetrain. This results in quiet operation. So if the rocker arms are clattering, it tells you something is amiss (bad lifter or worn or damaged parts) or the rocker arms need adjusting.
Inspect the valvetrain components. Excessive wear on the ends of the rocker arms, cam followers (overhead cam engines) and/or valve stems can open up the valve lash and cause noise. So too can a bent pushrod or a broken valve spring.

ENGINE BEARING NOISE

A deep rapping noise from the engine is usually "rod knock," a condition brought on by extreme bearing wear or damage. If the rod bearings are worn or loose enough to make a dull, hammering noise, you're driving on borrowed time. Sooner or later one of the bearings will fail, and when it does one of two things will happen: the bearing will seize and lock up the engine, or it will attempt to seize and break a rod. Either way your engine will suffer major damage and have to be rebuilt or replaced.
Bearing noise is not unusual in high mileage engines as well as those that have been neglected and have not had the oil and filter changed regularly. It can also be caused by low oil pressure, using too light a viscosity oil, oil breakdown, dirty oil or dirt in the crankcase, excessive blowby from worn rings and/or cylinders (gasoline dilutes and thins the oil), incorrect engine assembly (bearings too loose), loose or broken connecting rod bolts, or abusive driving.
Bearing wear can be checked by dropping the oil pan and inspecting the rod and main bearings. If the bearings are badly worn, damaged or loose, replacing the bearings may buy you some time. But if the bearings are badly worn or damaged, the crankshaft will probably have to be resurfaced -- which means a complete engine overhaul or replacing the engine is the vehicle is worth the expense.

Engine Noise Under Load

Symptom
Possible Cause
A cold piston knock for up to a minute and a half after starting a cold engine may be normal. This may be due to increased clearance between the pistons and cylinders. But once the engine warms up, the knocking noise should disappear.
If you hear a low rumble or knocking noise when the engine is warm, the most likely cause may be a bad rod bearing on the crankshaft (which may lead to bearing failure and/or rod breakage or crankshaft damage).
Low oil pressure
Check oil pressure at the oil pressure sending unit port on the engine with a gauge. .
If oil pressure is okay, replace sending unit.
Detonation or spark knock May be due to low octane fuel, carbon buildup in combustion chambers, over advanced ignition timing, inoperative EGR, or engine overheating.
Check all of these to determine the cause..
Loose torque converter bolts
Inspect the torque converter bolts and flywheel.
Repair as required.
Cracked flywheel - automatic transmission
Inspect the flywheel bolts and flywheel.
Repair as required.
Excessive connecting rod or main bearing clearance
Inspect connecting rod bearings , connecting rods and crankshaft. Use Plastigage or a feeler gauge to measure assembled bearing clearances.
Excessive Piston clearance
Piston slap may be due to worn cylinders, worn pistons or excessive piston-to-cylinder clearance

Dash Warning Lights

CHECK ENGINE LIGHT

Also called the "Malfunction Indicator Lamp" or (MIL), means your vehicle has detected a potential emissions fault. The computer has logged one or more diagnostic trouble codes that correspond to the problem and turned on the warning lamp to alert you to the problem.
There is NO WAY to determine the nature of the problem without connecting a scan tool to the vehicle's diagnostic connector to read the fault code(s). Once this has been done, further diagnosis and testing may be required to isolate the fault so the correct parts(s) can be replaced.
Don't be alarmed by a CHECK ENGINE light. Often the problem is something minor that will NOT affect the way your engine runs, or you car's ability to start or drive. Depending on the nature of the fault, your engine may not run as good as it normally does, or it may use more fuel than usual. But usually the problem does NOT require immediate attention. You can continue to drive your car until it can be diagnosed.
problem in an emissions control system or device.

OIL PRESSURE WARNING LIGHT

If a warning light says OIL or you see a little icon of an oil can, DO NOT ignore this warning light. It means your engine is not getting normal oil pressure. Stop driving immediately, turn the engine off and check the engine's oil level. If low, add oil to bring the level up to the FULL mark on the dipstick.
The oil pressure warning light comes on when oil pressure drops below a minimum threshold (the exact pressure will vary from one vehicle to another). No engine will run very long if it runs out of oil. The bearings will run dry, overheat and seize, causing severe engine damage (spun bearings, damaged crankshaft journals, broken connecting rods, etc.).
The underlying cause of a low oil pressure warning light is usually a low oil level in the engine's crankcase. This, in turn, may be due to leaky gaskets or seals, or worn valve guides, piston rings and/or cylinders that are causing the engine to burn oil. Leaky gaskets and seals are usually not too expensive to replace (except for the rear main crankshaft seal which is difficult and expensive to replace). The only fix for a worn engine that is burning oil is to overhaul or replace the engine (very expensive!)
Other causes of an low oil pressure warning light include a worn oil pump or a faulty oil pressure sending unit.


TEMPERATURE WARNING LIGHT

A TEMP warning light or an icon of a thermometer is another warning lamp that you should NOT ignore. Stop driving immediately, turn the engine off and let the engine cool for at least 30 minutes. Then check the coolant level in the coolant reservoir or radiator.
CAUTION: DO NOT open the radiator cap on a hot engine. Hot water and/or steam can spray out and scald you.
The temperature warning lamp is on because your engine overheated. Continuing to drive can cause expensive engine damage (head gasket failure, cracks in the cylinder head, piston scuffing, valve stem galling, etc.)
Your engine may have overheated for a variety of reasons. The most common cause is a low coolant level (check the radiator, hoses and engine for coolant leaks). Other common causes include a stuck thermostat, a cooling fan that is not working, a failed water pump, obstructions that block airflow through the radiator (bugs, debris, plastic bags), a buildup of scale or sludge inside your cooling system, or overworking your engine or air conditioning system during unusually hot weather. Towing a heavy trailer or prolonged mountain driving may also cause your engine to run hotter than normal.
If the coolant level is low, add coolant after the engine has cooled off. Check for leaks. If you see none, start the engine and cautiously proceed. If the engine starts to overheat again, your engine may have an internal coolant leak (Bad news because it means a leaky head gasket or cracks in the cylinder head or block), or there is some other problem (bad thermostat, water pump, etc.).
If you see a coolant leak, you may be able to temporarily stop the leak by adding a can of cooling system sealer to the radiator. This may temporarily plug the leak or slow it down enough so you can continue driving until the leak can be fixed.


CHARGING SYSTEM WARNING LIGHT

The "GEN" or "ALT" warning light, or an icon of a battery usually means trouble (on some vehicles, a battery icon may illuminate if there is a charging system problem). You do NOT have to stop immediately, but your drive time will be limited: maybe 30 minutes or so during the daytime, or less after dark. The reason for this is that your car will be running off the battery alone, so as long as the battery lasts you can continue to drive. Eventually, the battery will go dead causing your fuel pump and/or ignition system to stop working. To maximize your remaining drive time, turn off all accessories to minimize the electrical drain on the battery. If you're driving at night, DO NOT turn off your lights (too dangerous!). Pull off at the first opportunity and seek help.
This warning light comes on when the charging system is NOT producing enough current or voltage to meet your vehicle's electrical needs. The cause may be a failed alternator or generator, a failed voltage regulator (if separate from the alternator), loose or corroded battery cables, or a broken or slipping drive belt. Turn the engine off and check the belt that turns the alternator. Caution: DO NOT get your fingers, clothing or tools near the belt(s) or pulleys while the engine is running.
If the belt appears to be intact and is turning the alternator, start the engine, and turn on the headlights. If the lights are dim, it verifies the charging system is not working -- probably due to a failed alternator or other electrical fault.

BRAKE WARNING LIGHT

More bad news -- but not always. The Brake Warning light may be one for one of two reasons: you forgot to release the parking brake, or your brake system has a potentially serious hydraulic problem that may make your vehicle unsafe to drive.
First, check the parking brake lever, handle or pedal. Make sure it is fully released. If that is not the problem, test the brakes by pressing on the brake pedal. If the light comes on only while pressing the pedal, it means one of the hydraulic circuits in the brake system has lost pressure -- probably because of a leak (bad brake hose, leaky disc brake caliper or drum brake wheel cylinder). Your vehicle may or not be able to stop with this kind of problem, making it unsafe to drive. If the pedal feels unusually low or goes to the floor, DO NOT attempt to drive the vehicle. Have it towed to a service facility for repairs (or fix it yourself).
If the Brake Warning light remains on all the time, the problem may be a low fluid level in the master brake cylinder reservoir. Many vehicles have a fluid level sensor that comes on if the fluid level gets low. This may also occur when braking hard or braking on an incline because of the fluid sloshing inside the reservoir. Check the brake fluid level and add fluid as needed if low. The brake system should also be inspected for leaks or worn linings.

ABS WARNING LIGHT

This warning lamp means your anti lock brake system has detected a fault. When this happens, the ABS system logs one or more fault codes that correspond to the problem and turns on the ABS warning light. In most cases, it also temporarily DISABLES your ABS system. You vehicle should still brake and stop normally, but it will NOT have anti lock braking when making a sudden panic stop or braking on wet or slick surfaces. You can continue driving, but you should have the problem diagnosed and repaired at your earliest convenience.
NOTE: If the Brake Warning light is also on, it may indicate a serious hydraulic problem with the brake system. Your vehicle may NOT be safe to drive (see the info on Brake Warning Light above).

LOW TIRE WARNING LIGHT

low tire pressure warning lightThis icon is a Low Tire Pressure Warning light. This light comes on if your vehicle's tire pressure monitoring system (TPMS) detects a tire that is more than 25 percent under-inflated. Driving on a low tire can be dangerous because it increases the risk of a tire blowout. A low tire can also cause your vehicle to brake unevenly, pull to one side, handle poorly and get reduced fuel mileage. If the TPMS Low Tire Warning light is on, check the air pressure in your tires as soon as possible, and inflate them to the recommended pressure.

LAMP OUT INDICATOR LIGHT

This is a warning that you have a lamp out: a headlight, taillight, stop light or turn signal indicator. You can continue to drive your vehicle, but with reduced visibility and safety. Be warned that law enforcement officers may stop you and issue you a warning ticket or a safety violation ticket.
Check all the lights on your vehicle when it is safe to do so (not in the middle of the highway at night!), and replace any bulbs that have burned out. In some cases, the problem might be a corroded or loose socket, loose or corroded wiring, or a blown fuse.

SEAT BELT LIGHT WARNING LIGHT OR CHIMES

This little icon means somebody forgot to buckle up. Seat belts save lives so always use them, even on short trips. Driving without being bucked up may result in a ticket and a fine for a safety violation.


AIR BAG WARNING LIGHT

A warning light that looks like this or says SRS should NEVER come on unless there is a fault in your vehicle's air bag system (supplemental restraint system or SRS). Like the engine computer and ABS computer, the air bag control module runs a self-check every time the vehicle is driven. If it finds a fault in a crash sensor, one of the air bag modules, the wiring or itself, it will set a code, turn on the warning light and disable itself. You can drive the vehicle but the air bag(s) will NOT deploy should you be involved in an accident. You should have the problem diagnosed and repaired at your earliest convenience.
LOW WINDSHIELD WASHER FLUID WARNING LIGHT
This is a reminder light that the fluid level is low in your windshield washer reservoir. Add fluid at your earliest convenience for safe driving.


DOOR AJAR WARNING LIGHT

This is a reminder light that one of the doors (or tailgate) is not completely closed. Check all the doors (and tailgate) to make sure they are all latched properly. Sometimes the metal contacts that tell your vehicle the door is closed become dirty or corroded, causing a FALSE indication that a door is ajar. Cleaning the contacts will usually solve this kind of problem

SERVICE REMINDER LIGHT

Many late model vehicles have an oil change reminder light that comes on when the engine computer estimates the oil needs to be changed. The calculations are based on hours of engine operation, vehicle speed, ambient temperatures and other operating conditions. You do NOT have to change the oil immediately, but neither should you postpone the recommended maintenance too long. Oil should be changed every 3,000 miles for short trip city stop and go driving (especially during cold weather), or every 5,000 to 7,500 miles for mostly highway driving. Refer to your vehicle owners manual for the recommended service intervals.
Many service reminder lights have a RESET button that allows you to turn off the light and reset the interval period. On some, though, a scan tool is required to turn off and reset the light.

MORE WARNING LIGHTS

Many vehicles have their own unique warning lights or icons to alert you when something is wrong. You can usually find these in the back of your vehicle owner's manual. Note: The appearance of some warning lights will vary depending on the country where the vehicle is sold. 
LABELS: ENGINE