P0304

Misfire - Related Circuits:

System Description
The Powertrain Control Module (PCM) monitors crankshaft and camshaft position to detect if the engine is misfiring. The PCM looks for a sudden drop in crankshaft speed. This test is executed in blocks of 100 camshaft revolution tests. It may take several tests to store a DTC and illuminate the Malfunction Indicator Lamp (MIL). Under light misfire conditions, it may also take more than one trip to set a DTC. Severe misfire will flash the MIL indicating that catalytic converter damage is possible.

Conditions for Setting the DTC
- The misfire total is greater than or equal to 12 counts
- The engine speed is between 459 RPM and 3400 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 for greater than 15 seconds
- The Throttle Position (TP) angle hasn't changed more than 8% in 1 second
- One or more of the following DTCs are not set P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0502, P0503, P0601, P1133, P1406, P1441.

Action Taken When the DTC Sets
- The 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 misfire is severe enough to cause catalyst damage.
- The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn "OFF" after three 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.
- DTCs can be cleared by using a scan tool.

Diagnostic Aids
- Whenever DTC P0304 is intermittent, refer to "Diagnosis by Symptom."

DTC P0304 - Cylinder 4 Misfire Detected (1 Of 3):

DTC P0304 - Cylinder 4 Misfire Detected (2 Of 3):

DTC P0304 - Cylinder 4 Misfire Detected (3 Of 3):

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
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 connection 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 fault 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 misfires that have occurred until the DTC is cleared.
10. No spark on one coil, may be caused by an open secondary circuit. Therefore, the coil's secondary resistance should be checked.
13. Use injector test light J 34780-2 to test the harness wiring and for PCM control of the injectors.
14. Perform the "Injector/Coil Balance Test Procedure" on the misfiring cylinder only.
16. Determines if the injector driver circuit is shorted to ground or voltage or if the PCM is faulty.
20. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.
22. Replace any spark plugs that are worn, cracked or fouled.
27. Since voltage is supplied to the injector on a single circuit before the injector harness, the fault could only be a poor connection or open in the injector harness. An open before the harness would result in a "Cranks But Won't Run" complaint.
28. A basic engine problem that affects only cylinder #4 is possible at this point (i.e. valve train, compression, etc.).