GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 HHR 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0300

DTC Descriptor

DTC P0300: Engine Misfire Detected

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Description

The engine control module (ECM) 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 ECM 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 ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

Conditions for Running the DTC
    • DTCs P0013, P0014, P0107, P0108, P0117, P0118, P0125, P0128, P0218, P0220, P0315, P0336, P0502, P0503, P1114, P1115, P2125, P2135 are not set.
    • The engine is running.
    • The engine coolant temperature (ECT) is between -7 to +130°C (+19 to +266°F).
    • The throttle angle is steady.
    • The A/C compressor clutch is not changing state.
    • The fuel level is above 10 percent.
    • The fuel cut-off or decel fuel cut-off (DFCO) mode is not active.
    • The ECM is not receiving a rough road signal.
    • DTC P0300 runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM 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
    • You must preform the Crankshaft Position System Variation Learn before proceeding with this diagnostic procedure.
    • If condition is intermittent or not active, refer to Testing for Intermittent Conditions and Poor Connections .

Reference Information

Schematic Reference

    •  Engine Controls Connector End Views
    •  Ground Distribution Schematics

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Special Tools Required

    • J 26792 HEI Spark Tester
    • J 36012-A Ignition System Diagnosis Harness

Circuit/System Verification
    • There should be no abnormal engine noise.
    • Diagnose any other DTCs that are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
    • With a scan tool, observe the Misfire Current Counters.
    • Operate the engine within the conditions listed in the Freeze Frame Failure Records.
    • The engine should not be misfiring.

Circuit/System Testing
  1. Operate the engine within the conditions listed in the Freeze Frame Failure Records.
  2. A current misfire should not be indicated.
    3. ⇒If a single cylinder Current Misfire is indicated, inspect the following components of the affected cylinder for proper operation:
    • The ignition coil--Refer to Electronic Ignition (EI) System Diagnosis .
    • The spark plug--Refer to Spark Plug Inspection .
    • The fuel injector--Refer to Fuel Injector Diagnosis .
         ⇒If more than one cylinder is randomly misfiring, inspect the following components condition and operation:
    • The vacuum hoses and seals--Refer to Emission Hose Routing Diagram .
    • The throttle body and intake manifold
    • The crankcase ventilation system--Refer to Crankcase Ventilation System Inspection/Diagnosis .
    • The ECM grounds
    • The exhaust system--Refer to Restricted Exhaust .
    • The fuel--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The spark plugs--Refer to Spark Plug Inspection .

Repair Verification

If the customer concern was a flashing MIL perform the following procedure:

  1. Operate the vehicle at 2,500 RPM for 4 minutes.
  2. Operate the vehicle within the Conditions for Running DTC P0420. Refer to DTC P0420 .
    3. ⇒If DTC P0420 does not run and pass, diagnose that DTC.
  3. Clear the DTCs with a scan tool.
  4. Turn OFF the ignition for 30 seconds.
  5. Start the engine.
  6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
    7. ⇒If the DTC fails this ignition, a misfire still exists.