DTC P0300-P0308 - ENGINE MISFIRE DETECTED Pontiac Firebird IV

Note. DTC P0300 is set when the ECM recognizes a general misfire in the engine. If the ECM determines the cylinder causing the misfire it will set a specific DTC P0301-P0308, to indicate the number of the cylinder causing the misfire. If a DTC P0301-P0308 is retrieved, use this procedure to diagnose the misfire condition in the indicated cylinder.

Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .

Circuit Description

Misfire is detected using Camshaft Position (CMP) and Crankshaft Position (CKP) sensors. When PCM senses CKP deceleration not associated with normal engine speed reduction, CMP is used to determine misfiring cylinder. PCM determines misfires on each cylinder and evaluates a random misfire and set DTC.

Conditions required to set code are

1. No transaxle or VSS DTCs set.
2. No CKP, CMP, ECT, MAF or TP sensor DTCs set.
3. Engine speed 450-5800 RPM.
4. ECT 19-248°F (-7 to 120°C).
5. Throttle steady.
6. PCM detects crankshaft RPM variation, indicating a misfire which could cause catalytic convertor damage or high emissions.