Diagnosis Conditions

A cycle of 1,000 crankshaft revolutions is evaluated (for misfire damaging to the TWC, 200 crankshaft revolutions). The misfire rates are compared with a threshold value. If the misfire rate is greater than the threshold value, a fault is recorded in the memory.

The Check Engine Malfunction Indicator Lamp (MIL) is switched on and stays on when the misfire rate lies above the threshold value at which the emission limit values are exceeded during two consecutive driving cycles.

If the misfire rate may lead to permanent damage to the TWC, the Check Engine MIL flashes. If this misfire rate is subsequently no longer reached, the MIL changes to a continuous light.

NOTE: When the fuel tank is driven to empty, misfiring can occur. For this reason the fuel level in the tank is also stored in the memory when misfiring occurs. If the tank was empty, there was probably no fault. Erase fault memory and road test vehicle.

In the event of a short circuit to B+ or ground of the oxygen sensors ahead of the TWC, the mixture becomes too lean or too rich. This can cause misfiring. If, in addition, an oxygen sensor signal fault ahead of the TWC is stored in memory, first correct this fault and then road test the vehicle.

Fig 1: DTC P0300-P0306 Fault Conditions

Courtesy of PORSCHE OF NORTH AMERICA, INC.

NOTE: If the battery was disconnected, at least range 1 must be adapted before troubleshooting is carried out. See TWC damaging misfiring and State: Adaption 1 .