For 1990-2009 cars

### 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 Descriptors

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

### 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 P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0315, P0335, P0336, and P0502 are not set.

• | Engine speed is between 600-6,500 RPM.

• | The ignition 1 voltage is between 11-16 volts.

• | The engine coolant temperature (ECT) is between -7 and +120°C (+19 and +248°F).

• | The A/C compressor clutch is not changing states.

• | The fuel tank level is more than 15 percent.

• | The ECM is not in fuel cut-off or decel fuel cut-off mode.

• | The ECM is not receiving a rough road signal.

• | The throttle angle is steady within 10 percent.

• | The throttle angle is less than 4 percent when the vehicle speed is more than 10 km/h (6 mph).

• | The transmission is not changing gears.

• | The antilock brake system (ABS) and the traction control system (TCS), if equipped, is not active.

• | The DTCs run 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

DTCs P0300, P0301, P0302, P0303, and P0304 are Type A (MIL flashing) or Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0300, P0301, P0302, P0303, and P0304 are Type A (MIL flashing) or Type B DTCs.

### 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

• | The malfunction indicator lamp (MIL) will continue to flash

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### 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

Important: Perform the Crankshaft Position System Variation Learn before proceeding with this diagnostic procedure.

1. Engine running at the normal operating temperature, verify there is no abnormal engine noise.

⇒ | 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, P0315, P0335, P0336, P0351, or P0352 is not set.

⇒ | 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. Observe the scan tool Misfire Current Counter parameters. The Misfire Current Counters should not be incrementing.
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 the following conditions do not exist:

• | 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.

• | Restricted exhaust system--Refer to Restricted Exhaust.

⇒ | 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 to the boot of a spark plug wire and ground.

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.

⇒ | If there is no spark, test the spark plug wire for the correct resistance. Refer to Ignition System Specifications. Replace the spark plug wire if necessary. 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 the following conditions do not exist with the spark plug:

• | 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, observe the scan tool Misfire Current Counters. The misfire should not follow the spark plug exchange.

⇒ | If the misfire follows the spark plug, replace the spark plug.

8. If all conditions test normal, test or inspect for the following:

• | 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 Replacement

### Repair Verification

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.