Powertrain Controls Diagnosis

DTC P0300

SYSTEM DESCRIPTION
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring 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 (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0220, P0315, P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1120, P1258 are not set.
- The engine speed is between 450-5,000 RPM.
- The ignition voltage is between 10-18 volts.
- The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).
- The fuel level is more than 10 percent.
- The throttle angle is steady within 1 percent.
- The antilock brake system (ABS) and the traction control system (TCS) are not active.
- The transmission is not changing gears.
- The A/C clutch is not changing states.
- The PCM is not in fuel shut-off or decel fuel cut-off mode.
- The PCM is not receiving a rough road signal.
- DTC P0300 runs continuously once the above conditions are met.

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

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
- Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:

- Thickness variation of the brake rotors - Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. - Symptoms - Hydraulic Brakes

- The drive shaft not balanced - Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction. Vibration Analysis - Driveline

- Worn or damaged accessory drive belt - Refer to Symptoms - Engine - 4.8L, 5.3L and 6.0L. Testing and Inspection

- There may be more or less cylinders actually misfiring than indicated by the scan tool.
- Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.
- If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank.

TEST DESCRIPTION

Steps 1 - 7:

Steps 8 - 20:

Steps 21 - 23:

The number below refers to the step number on the diagnostic table.
2. If the actual CKP variation values are not within the learned values, the misfire counters may increment.