P0303

CIRCUIT DESCRIPTION
The powertrain control module (PCM) times the intervals between each pulse of the crankshaft position (CKP) sensor and compares each time interval with the other 7 to determine when an excessive change in crankshaft speed has occurred. This pulse is generated from a 4X reluctor wheel located on the front of the crankshaft. If the crankshaft speed is less than an expected amount, the PCM will increase the amount of fuel needed to correct the misfire. If the amount of fuel exceeds the calibrated value, the PCM will interpret this as a misfire and set the DTC. The misfire diagnostic is used only to identify a weak cylinder needing additional fuel. This diagnostic will only run once per ignition cycle.

CONDITIONS FOR RUNNING THE DTC
^ The engine coolant temperature (ECT) is more than 56°C (132°F).
^ The engine is idling for a total of 90 seconds.

CONDITIONS FOR SETTING THE DTC
The amount of fuel added is more than the calibrated value (internal to PCM).

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
The most likely cause for this DTC is the following:
^ A mechanical failure causing low cylinder compression
^ A fuel leak at the high pressure fuel injection lines or injection nozzles
^ A fuel injection nozzle stuck closed

If an injection nozzle is suspected, the injection nozzle can be transferred to another cylinder to determine if the DTC follows the nozzle.

After the repair has been performed, the vehicle may take approximately 30 seconds to return to a stable idle.

TEST DESCRIPTION

Steps 1-7:

The numbers below refer to the step numbers on the diagnostic table.
2. This step helps identify a suspected cylinder.
4. This step identifies an area with the mostly likely cause of failure.