P0304

Diagnostic Chart:

Wiring Diagram:

SYSTEM DESCRIPTION

The Powertrain Control Module (PCM) monitors both the crankshaft and camshaft position in order to detect engine misfire. The PCM looks for the rapid decrease in crankshaft speed associated with engine misfire once every 100 camshaft revolutions. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and illuminating the Malfunction Indicator Lamp (MIL). Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under severe misfire, the PCM flashes the MIL. A flashing MIL signals that a misfire capable of damaging the catalytic convener is detected. The Torque Converter Clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).

CONDITIONS FOR SETTING THE DTC

^ The misfire total is greater than 12 counts.

^ The engine speed is between 469 RPM and 6000 RPM.

^ The battery voltage is between 9 volts and 17 volts.

^ The Engine Coolant Temperature (ECT) is between -7°C (20°F) and 123°C (254°F).

^ The engine has been running more than 15 seconds.

^ The Throttle Position (TP) hasn't changed more than 8% in 1 second.

^ DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, P1404, and P1621 not set.

ACTION TAKEN WHEN THE DTC SETS

The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.

OR

The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

OR

The MIL will illuminate immediately and flash if a misfire is severe enough to cause catalyst damage. The Torque Converter Clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set. (automatic transmission only) The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. A history DTC is stored.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.

^ A scan tool can clear the DTCs.

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. Whenever the DTC is an intermittent, refer to the Driveability Symptom Tables.
Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.

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. A visual/physical 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.

^ For air leaks at the throttle body mounting area and intake manifold sealing surfaces.

4. This step determines if DTC P0304 is the result of a hard malfunction or an intermittent condition.

6. When the misfire is not present, operate the vehicle to the conditions found in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators start to increment, then misfire is present. A history misfire counter will store the number of the misfires that have occurred until the DTC is cleared. The current counter must count a total of at least 195 misfires before writing to the history counter.

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 light J 34780-2 to test the harness wiring and for PCM control of the injectors.

14. Perform the Injector Coil Test Procedure on the misfiring cylinder only.

16. Determines if the injector driver circuit is shorted to ground, voltage or if the PCM is malfunctioning.

20. Before replacing the PCM, check the terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline information for PCM reprogramming and also refer to the Crankshaft Position (CKP) System Variation Learn Procedure for the Crankshaft Position System Variation Procedure.

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 could only be a poor connection or an open in the injector harness. An open before the harness would result in a Cranks But Does Not Run complaint.

28. A basic engine problem that affects only cylinder #4 is possible at this point (i.e. valve train, compression, etc.).