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PKRWUD · 12-11-2002, 12:05 PM

The MIL (Malfunction Indicator Lamp, aka: Check Engine Light) will flash every time the ECM detects that something is not quite right. If a sensor sends back a signal that is not within the preprogrammed parameters, or if device that it told to do something didn't do what it was told, the ECM makes a note of this, and saves it as a code in continuous memory. It stays there for a period of 100 (average, some ECM's save it longer, some save it for fewer) cycles of the ignition switch. A cycle is each time the key is turned on and then off. If the event doesn't repeat itself during that time, the ECM erases it from continuous memory. If it does reoccur, the 100 cycle count starts all over again. The ECM triggers the MIL to flash when it makes this note to itself, alerting the driver that a problem was detected, and a code was stored, and that they might want to get it checked.

If the problem is one that doesn't change, and continuously triggers a problem, the MIL stays lit, basically because the ECM is continuously making a note of it, which continuously flashes the MIL. The hope here is that the driver realizes there is a constant problem, and will have it looked at immediately. Once it no longer detects the problem, the light goes off, and the 100 cycle count begins. That does not mean that everything is okay, however.

In short, every time the MIL flashes, the ECM stores the code for no fewer than 75 ignition cycles (usually 100). These codes will be stored as Continuous codes, and are read during a KOEO (Key On, Engine Off) search for codes.

When the codes are to be pulled, first a KOEO test is run. The engine needs to be at operating temp for this. The ECM then activates each of it's devices, and makes sure they all are responding. This is why you will hear clicks and buzzes while this test is being performed.

If any problems are found, those codes will come up first, followed by any continuous codes that are in memory. These codes must be corrected before the next stage in reading codes is performed.

The next stage is the KOER (Key On, Engine Running) test. It is critical that the engine be warmed up completely before starting this test. Some vehicles are required to depress the clutch pedal during the entire test, and there is usually a point during the test where you need to crank the steering wheel, and depress the brake pedal. lastly, there will be a point at which you need to quickly move the gas pedal to WOT.

When this test is finished, the codes that will be there will tell about problems the ECM found while running it's range of tests under running conditions.

Sooooo, anytime you see the MIL flash, you really should run the KOEO test, and see what codes are found.

Take care,
~Chris

12-11-2002, 12:05 PM	#10
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	The MIL (Malfunction Indicator Lamp, aka: Check Engine Light) will flash every time the ECM detects that something is not quite right. If a sensor sends back a signal that is not within the preprogrammed parameters, or if device that it told to do something didn't do what it was told, the ECM makes a note of this, and saves it as a code in continuous memory. It stays there for a period of 100 (average, some ECM's save it longer, some save it for fewer) cycles of the ignition switch. A cycle is each time the key is turned on and then off. If the event doesn't repeat itself during that time, the ECM erases it from continuous memory. If it does reoccur, the 100 cycle count starts all over again. The ECM triggers the MIL to flash when it makes this note to itself, alerting the driver that a problem was detected, and a code was stored, and that they might want to get it checked. If the problem is one that doesn't change, and continuously triggers a problem, the MIL stays lit, basically because the ECM is continuously making a note of it, which continuously flashes the MIL. The hope here is that the driver realizes there is a constant problem, and will have it looked at immediately. Once it no longer detects the problem, the light goes off, and the 100 cycle count begins. That does not mean that everything is okay, however. In short, every time the MIL flashes, the ECM stores the code for no fewer than 75 ignition cycles (usually 100). These codes will be stored as Continuous codes, and are read during a KOEO (Key On, Engine Off) search for codes. When the codes are to be pulled, first a KOEO test is run. The engine needs to be at operating temp for this. The ECM then activates each of it's devices, and makes sure they all are responding. This is why you will hear clicks and buzzes while this test is being performed. If any problems are found, those codes will come up first, followed by any continuous codes that are in memory. These codes must be corrected before the next stage in reading codes is performed. The next stage is the KOER (Key On, Engine Running) test. It is critical that the engine be warmed up completely before starting this test. Some vehicles are required to depress the clutch pedal during the entire test, and there is usually a point during the test where you need to crank the steering wheel, and depress the brake pedal. lastly, there will be a point at which you need to quickly move the gas pedal to WOT. When this test is finished, the codes that will be there will tell about problems the ECM found while running it's range of tests under running conditions. Sooooo, anytime you see the MIL flash, you really should run the KOEO test, and see what codes are found. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!