P0304

CIRCUIT DESCRIPTION
The powertrain control module (PCM) uses information from the ignition control module (ICM) and the crankshaft position (CKP) 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 three-way catalytic (TWC) converter to overheat under certain conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC converter overheating are present.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, or P1621 are not set.
^ The engine speed is between 469-6,400 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 throttle position (TP) has not increased more than 8 percent in 1 second.
^ The TP has not decreased more than 1.5 percent in 1 second.

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed 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.
^ Clear the MIL and the DTC with a scan tool.

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

When checking the electrical terminal connections with a test lamp or DMM, a malfunctioning electrical terminal connection may be cleaned and not detected as a problem. You may also clean a corroded or dirty electrical terminal connection when disconnecting and reconnecting any electrical connector.

TEST DESCRIPTION

Steps 1-7:

Steps 8-11:

The numbers below refer to the step numbers on the diagnostic table.
1. The Diagnostic System Check-Computers and Controls Systems prompts you to complete some of the basic checks and to store the Freeze Frame/Failure Records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data on the scan tool for later reference.
2. If a DTC P0201-P0204 is present, the condition causing the misfire is in the fuel injector circuitry. The DTC P0201-P0204 table will diagnose the fuel injectors and circuitry.
4. This step determines if the DTC is the result of a hard malfunction or an intermittent condition.
5. This step tests the systems ability to produce at least 25,000 volts at the spark plug.
8. No spark on one coil terminal may be caused by an open secondary circuit.
10. Conditions for Running the DTC P0420 need to be run in order to determine if the catalyst has been damaged from the misfire.