P0303

Diagnostic Chart:

Diagnostic Chart (cont'd):

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. 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 3 consecutive passed trips meeting the same misfire criteria or 80 passed trips if the criteria has not been met.

DTC PARAMETERS

DTC P0301 (Cylinder 1), or DTC P0302 (Cylinder 2), or DTC P0303 (Cylinder 3), or DTC P0304 (Cylinder 4) will set if a misfire has 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 -6.75° and 118°C (20° and 244°F).
^ Throttle change is not rapid.
^ Not in DFCO mode (Decel Fuel Cutoff).
^ Ignition voltage is between 8-15 volts.
^ No TP, CKP, IAT, MAP, ECT DTCs have been set.

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

DIAGNOSTIC AIDS

When attempting to diagnose an intermittent problem use the Scan tool to review Malfunction history diagnostic information. This supplemental data can be used to duplicate a problem.

If an injector, IC or EGR DTC is active and the misfire DTC is active diagnose the other DTCs first. 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 tools active misfire counts should pick up an intermittent misfire problem. Watch the misfire counter. If a specific cylinder misfires under certain load conditions, it may be duplicated in the stall.

^ Injector resistance - 12 ohms.
^ Wire resistance - under 12 K ohms.
^ Spark plug gap - 0.060 in.
^ Coil pack secondary resistance (tower to tower) is 7-9 K ohms.
^ Wire positioning on coils: 4-1-2-3.