P0300

Diagnostic Chart:

Wiring Diagram:

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 or 80 passed trips if the criteria has not been met.

DTC PARAMETERS
DTC P0300 will set if random misfires have been detected after a series of tests when:
^ Engine speed is between 469 or 7188 rpm.
^ Traction control fuel cutoff is not active.
^ Engine coolant is between 6.750 and 118°C (20° and 244°F).
^ Throttle change is not rapid.
^ Not in decel fuel cut-off mode (DFCO)
^ Ignition voltage is between 8-15 volts.
^ No TP Sensor, CKT, IAT, MAP or ECT 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, EST or EGR DTC is active and a misfire is active, diagnose those DTCs first (injector, EST,EGR).

Use the Scan tool to monitor active misfire counts. Spraying water on wires provides a good path for current to flow to ground on a bad wire. 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 ohms
^ Wire resistance - under 12K ohms
^ Spark plug gap - 0.040 in
^ Coil pack secondary resistance (tower to tower) - 8-15 K ohms
^ Wire positioning on coils 4-1-2-3 connector