DeVille d Elegance V8-4.6L VIN Y (1998)
Powertrain Control Module: Description and Operation
Special Cases of Type B Diagnostic Tests
Description
Fuel trim and misfire are special cases of type B DTCs.
Operation
Each time a fuel trim or misfire malfunction is detected, engine load, engine speed, and engine coolant temperatures are recorded. In order for the fuel
trim or misfire DTCs to report a PASS the load conditions must be within 10%, the speed conditions must be within 375 rpm, and the coolant
temperatures must be in the same calibratable high or low range at the time the diagnostic test last reported a failure. When the ignition is turned off, the
last reported set of conditions remain stored. During subsequent ignition cycles, the stored conditions are used as a reference for similar conditions. If a
malfunction occurs during two consecutive trips, the Diagnostic Executive treats the failure as a normal type B diagnostic, and does not use the stored
conditions. However, if a malfunction occurs on two non-consecutive trips, the stored conditions are compared with the current conditions. The MIL will
then illuminate under the following conditions:
^
When the engine load conditions are within 10% of the previous test that failed.
^
Engine speed is within 375 rpm, of the previous test that failed.
^
Engine coolant temperature is in the same range as the previous test that failed.
Unique to the misfire diagnostic, the misfire DTC has the ability of alerting the vehicle operator to potentially damaging levels of misfire. If a misfire
condition exists that could potentially damage the catalytic converter as a result of high misfire levels, the PCM will command the MIL to flash at a rate
of once per second during the time that the catalyst damaging misfire condition is present.
