P0303

SYSTEM DESCRIPTION
The Powertrain Control Module (PCM) uses information from the Ignition Control (IC) module and the Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter to overheat under certain conditions. The Malfunction Indicator Lamp (MIL) will flash ON and OFF when the conditions for 3-way catalytic converter overheating are present.

CONDITIONS FOR RUNNING THE DTC
^ The engine speed is between 469-5,906 RPM
^ The battery voltage is between 9-17 volts
^ The engine Coolant Temperature (ECT) is between -7 to +123°C (20-254°F)
^ The engine has been running more than 5 seconds
^ The fuel level is above 10 percent

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire rate sufficient to cause the emissions levels to exceed a mandated standard.

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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.

TEST DESCRIPTION

Steps 1-11:

Steps 12-23:

Steps 24-31:

The numbers below refer to the step numbers on the diagnostic table:
2. Whenever a DTC P0108 is present, verify that no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of a misfire.
3. An inspection should include checking the following conditions:
^ The wiring for proper connections, pinches, and cuts
^ Clean and tight PCM grounds
^ The vacuum hoses for splits, kinks, and proper connections as shown on the vehicle emission information label-Check thoroughly for any type of leak or restriction.
4. This step determines if the Misfire DTC is the result of a hard malfunction or an intermittent condition.
6. If the misfire is not present, operate the vehicle under the conditions found in the Freeze Frame Data in order to detect the misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. If the misfire accumulators start to increment, the misfire is present. A history misfire counter will record the number of misfires that occur until the DTC is cleared. The current counter must count a total of at least 195 misfires before the history counter begins storing the misfire information.
10. No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be checked.
13. Use the injector test lamp to test the harness wiring and for PCM control of the injectors.
14. Perform the Fuel Inj Coil Test on the misfiring cylinder only. Component Tests and General Diagnostics
16. Determines if the injector driver circuit is shorted to ground, voltage or if the PCM is malfunctioning.
22. Replace any spark plugs that are worn, cracked, or fouled.
27. Since the voltage is supplied to the injector on a single circuit before the injector harness, the malfunction may only be a poor connection or an open in the injector harness. An open before the harness may result in a Cranks But Does Not Run complaint.
28. A basic engine problem that affects only a single cylinder is possible at this point (i.e. valve train, compression, etc.).