P0300

Diagnostic Chart:

Schematic:

The PCM uses pulses from the crankshaft position sensor to determine the position and rpm of the engine at various degrees of rotation. The PCM can then base misfire diagnostics on the principle that crankshaft velocity will increase as each cylinder contributes its power input. Under certain conditions the PCM will perform a series of tests to determine misfire percentage on a cylinder based on crankshaft velocity variation. The MIL (SERVICE ENGINE SOON) light will flash if an active catalyst damaging misfire occurs (20-100%) and will illuminate On solid if an emission related misfire (2-19%) is present after two consecutive trips. The MIL (SERVICE ENGINE SOON) light will turn Off after three consecutive passed trips meeting the same misfire criteria. The torque converter is disabled momentarily to determine if the misfire was due to a rough road condition (automatic only).

DTC PARAMETERS
DTC P0300 will set if random misfires have been detected after a series of tests when:
^ More than 12 misfire counts.
^ Engine speed is between 469 or 6400 rpm.
^ Engine coolant is between -7° and 113°C (20° and 254°F).
^ Fuel level is greater than 10%.
^ The engine has been running at least 5 seconds.
^ Ignition voltage is between 9-17 volts.
^ No TP Sensor, CKP IAT MAP ECT O2 sensor, Fuel Trim Lean/Rich, Knock, CMP VSS, Idle Speed, ECM Memory, TCC, and PCM Long Term Memory DTCs have been set.

IMPORTANT: The misfire diagnostics are continually checked with engine running when the above conditions have been met.

DIAGNOSTIC AIDS
Verify crank learned procedure has matched PCM to crankshaft in vehicle.

If an injector or ignition system DTC is active and a misfire is active, diagnose other DTCs first.

Use the Scan tool to monitor active misfire counts. The Scan tool active misfire counts should pick up an intermittent misfire problem. Watch the Scan tool misfire counter. When a specific cylinder misfires under certain load, conditions may be duplicated in the stall.
^ Injector resistance - 12-13 ohms
^ Spark plug gap - 0.045 in