Catalyst-Damaging Misfire

Theory of Diagnostic Operation
The diagnostic check for catalyst damaging misfire runs constantly once the enabling criteria have been met. For every possible combination of engine operating conditions (rpm, load, temperature, etc.), the ECM has a value stored in it's memory telling it the maximum number of misfires which can take place every 200 crankshaft revolutions without harming the catalyst. Any time the number of misfires exceeds this value the MIL must begin to flash even if it is already illuminated steadily for another problem.

Flashing the MIL is intended to get the driver to back off the throttle before catalyst damage can occur. Once the engine is no longer misfiring severely enough to cause catalyst damage the MIL will change from flashing to steady illumination. A DTC will be set as soon as the MIL begins to flash.

The MIL will be switched off if there is no misfire under similar driving conditions for three driving cycles.

The DTC will be erased automatically when the MIL is oft and there has been no misfire detected for 40 warm-up cycles

Low Fuel DTC
Any time there is a misfire or fuel trim code and the fuel level has dropped low enough to turn on the low fuel warning light on the dash there will also be a Low Fuel DTC set in the TRIONIC or MOTRONIC system menu. Always check for this code so you don't waste time and money looking for a complicated explanation for fault codes set on an engine which stopped running because the tank was empty.