GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Caprice WM 🢒 DTC 🢒 DTC P0300-P0306

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

DTC P0301: Cylinder 1 Misfire Detected

DTC P0302: Cylinder 2 Misfire Detected

DTC P0303: Cylinder 3 Misfire Detected

DTC P0304: Cylinder 4 Misfire Detected

DTC P0305: Cylinder 5 Misfire Detected

DTC P0306: Cylinder 6 Misfire Detected

Circuit/System Description

The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensors 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. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring the DTC for that cylinder will set.

Conditions for Running the DTC
    • DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336 or P0338 are not set.
    • The engine speed is between 400-7,000 RPM and steady.
    • The engine run time is more than 45 seconds.
    • The delivered torque signal is more than 10 percent at idle.
    • The delivered torque signal is between 9-30 percent with the transmission in drive.
    • The intake air temperature (IAT) is more than -30°C (-22°F).
    • The A/C compressor not changing states.
    • The torque management is not active.
    • The antilock brake system/traction control system (ABS/TCS) is not active.
    • The ECM is not receiving a rough road signal.
    • The fuel level is more than 12 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 exist for at least 1000 engine revolutions.

Conditions for Setting the DTC

DTC P0300

The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value for more than 4 seconds.

DTC P0301, P0302, P0303, P0304, P0305 or P0306

The ECM detects a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards.

Action Taken When the DTC Sets

DTC P0300 is a type B DTC.

Conditions for Clearing the DTC

DTC P0300 is a type B DTC.

Diagnostic Aids

A misfire DTC may be caused by vibrations from sources other than the engine. Inspect for the following possible sources:

    • A tyre 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

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  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

Circuit/System Verification
  1. Engine idling at the normal operating temperature.
    2. ⇒If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical.
  2. Verify that DTCs: DTC P0011, P0014, P0021, P0024, P0201-P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0335, P0336, P0338, P0351-P0356, P2088, P2090, P2092, P2094, P2300, P2301, P2303, P2304, P2306, P2307, P2309, P2310, P2312, P2313, P2315 or P2316 are not set.
    3. ⇒If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  3. Observe the Misfire Current Cyl. 1-6 parameters with a scan tool. The Misfire Current Counters should not be incrementing
  4. Engine idling, using a scan tool perform the injector cut off test to isolate the misfiring cylinder. The engine speed should change when each injector is disabled.

Circuit/System Testing
  1. Verify that the following conditions do not 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.
    • Exhaust system restrictions.
         ⇒If you find any of the above conditions, repair as necessary.
  2. Ignition OFF, remove the ignition coil of the misfiring cylinder, but leave the electrical connector connected.
  3. Inspect the ignition coil boot for the following conditions:
    4. • Holes
    • Tears.
    • Carbon tracking.
    • Oil contamination.
    •  Water intrusion.
         ⇒If you find any of the above conditions, repair as necessary.
  4. Remove the fuel pump fuse from the fuse block.
  5. Install the a approved spark tester to the boot of the ignition coil and a known ground.

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

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

Repair Instructions
    •  Ignition Coil Replacement - Bank 1
    •  Ignition Coil Replacement - Bank 2
    •  Spark Plug Inspection

Repair Verification
  1. If the customer concern was a flashing malfunction indicator lamp (MIL), refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  2. Using a scan tool clear all DTCs
  3. Turn OFF the ignition for 30 seconds.
  4. Ignition On, engine running.
  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 cycle, a misfire still exists.