GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2008 🢒 G3 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0300

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0300: Engine Misfire Detected

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 3-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present.

Conditions for Running the DTC
    • DTCs P0107, P0108, P0122, P0123, P0335, P0336, P0337, P0341, P0342, P0400, P0401, P0403, P0404, P0405, P0406 and P0501 are not set.
    • Engine speed is between 800-4,500 RPM.
    • The ignition 1 voltage is more than 11 volts.
    • The engine coolant temperature (ECT) is more than -7°C (+20°F).
    • The A/C compressor clutch is not changing states.
    • The torque management is not active.
    • The fuel tank level is more than 20 percent.
    • The ECM is not in fuel cut-off or decel fuel cut-off mode.
    • The throttle angle is steady.
    • DTC P0300 runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value.

Action Taken When the DTC Sets

DTC P0300 is a Type A (MIL flashing) or Type B DTC.

Conditions for Clearing the DTC

DTC P0300 is a Type A (MIL flashing) or Type B DTC.

Diagnostic Aids

A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources:

    • A tire or wheel that is out of round or out of balance
    • Variable thickness brake rotors
    •  An unbalanced drive shaft
    • Certain rough road conditions
    • A damaged accessory drive component or belt

Reference Information

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 26792 Spark Tester

Circuit/System Verification
  1. Engine running at the normal operating temperature. Verify there is no abnormal engine noise.
    2. ⇒If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical .
  2. Observe the DTC information with a scan tool. Verify that DTC P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0335, P0336, P0337, P0351, or P0352 is not set.
    3. ⇒If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

    Important: A misfire may only occur when the engine is under a load. An engine load may be necessary to verify the condition.

  3. Engine running, disconnect one fuel injector connector at a time to isolate the misfiring cylinder. The engine speed should change when an injector is disconnected.
  4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
  1. Verify none of the following conditions exist:
    2. • Vacuum hose splits, kinks, and incorrect connections
    • Engine vacuum leaks
    • Crankcase ventilation system for vacuum leaks
    • Fuel pressure that is too low or too high--Refer to Fuel System Diagnosis .
    • Contaminated fuel--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Exhaust system restrictions
         ⇒If you find any of the above conditions, repair as necessary.
  2. Ignition OFF, disconnect the spark plug wire from the misfiring cylinder.
  3. Install the J 26792 Spark Tester to the boot of a spark plug wire and ground.

    4. Important: An erratic or weak spark is considered a no spark condition.

  4. Attempt to start the engine and observe the J 26792 . The spark tester should spark.
    5. ⇒If there is no spark, test the spark plug wire for less than 1,000 ohms per foot (31 cm per meter). Replace the spark plug wire if more than the specified value. If the spark plug wire test normal, refer to Electronic Ignition (EI) System Diagnosis for diagnosis of the ignition coil.
  5. Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the following conditions do not exist with the spark plug:
    6. • Gas, coolant, or oil fouled--Refer to Spark Plug Inspection .
    • Cracked, worn, incorrectly gapped
    ⇒If there is a condition with the spark plug, replace the spark plug.
  6. Exchange the suspected spark plug with another cylinder that is operating correctly.
  7. Engine running, disconnect the injector that corresponds to the misfiring cylinder. The engine speed should change.
    8. ⇒If the engine speed changes, replace the spark plug.
  8. If all conditions test normal, test or inspect for the following:
    9. • A lean or rich fuel injector--Refer to Fuel Injector Solenoid Coil Test .
    • An engine mechanical condition--Refer to Symptoms - Engine Mechanical .

Repair Instructions
    •  Spark Plug Wire Replacement
    •  Spark Plug Replacement

Repair Verification

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

  1. If the customer concern was a flashing MIL, operate the vehicle within the Conditions for Running DTC P0420. Refer to DTC P0420 .
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. 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.
  6. If the DTC fails this ignition, a misfire still exists.