Other Warning Light(s) On
Temp Warning Light On
Your engine is overheating. Stop driving immediately and turn the engine off. Continuing to drive risks causing expensive engine damage such as a blown head gasket, or cracked or warped cylinder head.
Low oil pressure or loss of oil pressure can be caused by a low oil level in the crankcase, a worn or damaged oil pump, or worn engine bearings.
Allow the engine to cool down for several hours before you attempt any further diagnosis. A hot engine can be very dangerous because of steam pressure inside the radiator and coolant reservoir. Do NOT attempt to add coolant until the engine has cooled down and the radiator cap or reservoir cap can be safely opened. Overheating can be caused by a low coolant level (check the radiator, water pump, and hoses for leaks), coolant leaks inside the engine (leaky head gasket or cracks in the head or block), a stuck thermostat, or a cooling fan that isn't working (bad fan clutch, fan motor, or fan relay).
Oil Light On
Oil pressure is dangerously low. Stop driving immediately and turn the engine off. Continuing to drive risks the rapid failure of bearings and camshaft in your engine. Low oil pressure or loss of oil pressure can be caused by a low oil level in the crankcase, a worn or damaged oil pump, or worn engine bearings. In older high mileage vehicles, it is not uncommon to see the oil warning light flicker at idle because of internal engine wear. Check the oil level before restarting the engine. If low, check the engine for leaky gaskets and seals, or a loose oil filter. If no leaks are seen, the engine may be burning oil because of worn valve guides, rings, and/or cylinders. Add oil to bring the level on the dipstick up to the full mark, then start the engine to see if the light goes out. If the light does not go out and the engine is making noise (ticking, rattling, clicking, rapping sounds), it may not be getting normal oil pressure – or it may have suffered damage because of the loss of oil pressure. You’re looking at an overhaul or buying another engine.
Charging, Alt or Gen Light On
Your charging system is not putting out its normal voltage or current. This means one of two things: either the alternator (generator) has died, or the belt that drives it is slipping or has broken. On vehicles with serpentine belts, losing a belt means you lose everything that the belt drives: the water pump, alternator, power steering pump, and A/C compressor. The A/C compressor you can live without, and with sufficient upper body strength you can still steer without the PS pump. But your engine isn't going to stay cool for long without the water pump. So stop, turn the engine off and take a look under the hood to see if the belt is still intact. If the belt is still on and appears to have normal tension, the alternator has probably failed. You can probably drive your car a few miles or up to 30 minutes or so on the juice that’s left in the battery, but don’t count on going too far because, without the alternator, the battery will run down very quickly. And once voltage drops below a certain level, the engine electronics will shut down. The fix? Check the charging system’s output at the battery terminals with a voltmeter. Normal charging voltage should be about 13.5 to 14.5 volts (it varies some with temperature and load). If you see 12.6 volts or less (which is base voltage for a fully charged battery), you need to have the alternator tested (many parts stores can do this for you). Or, with the ignition in the accessory position and the lights on, the battery voltage should remain near 12 volts for several minutes. If not, you have a weak battery.
ABS or Brake Light On
If only the ABS light is on, your vehicle should still have normal braking (possibly without power assist, though, depending on what type of ABS system it has). But if the brake light is on (with or without the ABS light), it may indicate a serious hydraulic problem in your brake system. On most vehicles, the brake warning light will come on if a safety switch detects a difference in pressure between the brake circuits when the brakes are applied. This may indicate a leak and loss of pressure in one of the circuits. On some vehicles, there is also a brake fluid level sensor in the brake fluid reservoir on the master brake cylinder. If the fluid level drops, it may turn on the warning light. Either way, the first order of business is to stop the vehicle and check the fluid level in the master cylinder. The fluid level will drop somewhat as the brake linings wear, but a sudden drop in the level usually means there’s a leak in a brake line, hose, caliper or wheel cylinder. Do NOT drive the vehicle until the problem has been diagnosed and repaired.
Turning the Check Engine Lamp Off
As a rule, the Check Engine Light will remain on as long as a fault persists. If an intermittent fault does not reoccur after three consecutive trips, the MIL lamp will go out but the code will remain in memory. If the fault does not reoccur for 40 trips, the code will be erased. The only safe way to clear fault codes and turn the MIL lamp off is to use a scantool. On many pre-OBDII vehicles, all you had to do was disconnect the battery or pull the PCM fuse to clear the memory and turn the Check Engine Light off. If the problem had not been fixed, the Check Engine Light would eventually come back on. But this procedure should NOT be used on OBDII cars for the following reason:
WARNING: On many OBDII cars, pulling the PCM fuse or disconnecting the battery may NOT clear the codes - and may cause a loss of important information that the PCM needs to function correctly. On some vehicles, loss of power to the PCM may cause it to forget transmission settings, climate control functions, and other essential data. This, in turn, may require the use of a scantool and a special re-learning procedure to reset the PCM.
Here’s another thought: codes contain important diagnostic information you or somebody else might need to further troubleshoot and repair the system. If the codes are cleared, it may take some time for the codes to reset - which will delay diagnosing and repairing the fault. The best approach to turning off the light, therefore, is to read out the codes, and clear the codes carefully.