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 Descriptor

DTC P0300 00: Engine Misfire Detected
DTC P0301 00: Cylinder 1 Misfire Detected
DTC P0302 00: Cylinder 2 Misfire Detected
DTC P0303 00: Cylinder 3 Misfire Detected
DTC P0304 00: Cylinder 4 Misfire Detected

### Circuit/System Description

The engine control module (ECM) uses information from the crankshaft position sensor in order to determine when an engine misfire is occurring and uses information from the camshaft position sensor - intake and camshaft position sensor - exhaust sensors in order to determine which cylinder is misfiring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM is able to detect individual misfire events. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 00 sets. Under certain driving conditions, a misfire rate can be high enough to cause the 3-way catalytic converter to overheat, possibly damaging the converter. The malfunction indicator lamp (MIL) will flash ON and OFF when converter overheating, damaging conditions are present and DTC P0300 00 is set. DTCs P0301-P0304 00 correspond to cylinders 1-4. If the ECM is able to determine that a specific cylinder that is misfiring, the DTC for that cylinder will set.

### Conditions for Running the DTC

• | DTCs P0010 00, P0011 00, P0013 00, P0014 00, P0016 00, P0017 00, P0101 00, P0102 00, P0103 00, P0112 00, P0113 00, P0117 00, P0118 00, P0121 00, P0122 00, P0123 00, P0222 00, P0223 00, P0315 00, P0335 00, P0336 00, P0502 00, P0651 00, and P2135 00 are not set.

• | The engine speed is between 600 to 6528 RPM.

• | The ignition voltage is between 11 to 18 V.

• | The ECT sensor is between -7 to +125°C (+19 to +257°F).

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

• | The fuel tank level is greater than 15%.

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

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

• | The throttle angle is steady within 5%.

• | The throttle angle is greater than 3% when the vehicle speed is greater than 5 km/h (3 MPH).

• | The transmission is not changing gears.

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

• | DTCs P0300 00, P0301 00, P0302 00, P0303 00, and P0304 00 run 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 or catalytic converter damaging levels to exceed mandated standards.

### Action Taken When the DTC Sets

DTCs P0300 00, P0301 00, P0302 00, P0303 00 and P034 00 are Type A (MIL flashing) or Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0300 00, P0301 00, P0302 00, P0303 00 and P034 00 are Type A (MIL flashing) or Type B DTCs.

### Diagnostic Aids

• | A misfire may only occur when the engine is under a load or when the engine is cold.

• | A misfire DTC may 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

⇒ | Certain rough road conditions

⇒ | A damaged accessory drive component or belt

⇒ | A damaged reluctor wheel

• | High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition.

• | The MIL indicator flashes when there is an engine misfire.

### 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

#### Special Tools

• | EL-26792 HEI Spark Tester

• | J 36012-A Ignition System Diagnostic Harness

• | EL-34730-405 Injector Test Lamp

### Circuit/System Verification

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 P0201 00, P0202 00, P0203 00, P0204 00, P0315 00, P0335 00, P0336 00, P0351 00, P0352 00, P0353 00, or P0354 00 are not set.

⇒ | If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

Note: 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 that the following conditions do not exist:

• | Vacuum hose splits, kinks, and incorrect connections

• | Engine vacuum leaks

• | Crankcase ventilation system for vacuum leaks, refer to Crankcase Ventilation System Inspection/Diagnosis.

• | 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 harness connector at the appropriate Q17 Fuel Injector.
3. Connect the EL-34730-405 Injector Test Lamp between the control circuit terminal B and the ignition voltage circuit terminal A.
4. Engine idling, the test lamp should flash.

⇒ | If the test lamp does not flash, refer to DTC P0201, P0202, P0203, or P0204

5. Ignition OFF, connect the Q17 Fuel Injector connector. Remove the K35 Ignition Control Module assembly.
6. Inspect the ignition coil spark plug boots for the following conditions:

• | Damage

• | Carbon tracking

• | Oil contamination

• | Water intrusion

⇒ | If you find any of the above conditions, repair as necessary.

7. Connect the harness connector to the ignition coil assembly.

Note: It may be necessary to secure the J 36012-A Ignition System Diagnostic Harness to the spark plug boots with electrical tape.

8. Install the J 36012-A Ignition System Diagnostic Harness to the spark plug boots.
9. Install the EL-26792 HEI Spark Tester between the spark plug boot of the misfiring cylinder and ground.
10. Connect the remaining wires to the appropriate cylinders.

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

11. Attempt to start the engine and observe the EL-26792 HEI Spark Tester . The spark tester should spark.

⇒ | If there is no spark, refer to Electronic Ignition (EI) System Diagnosis

12. 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 LINK (Spark Plug Inspection).

• | Cracked, worn, incorrectly gapped

⇒ | If there is a condition with the spark plug, replace the spark plug.

13. Exchange the suspected spark plug with another cylinder that is operating correctly.
14. 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.

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

• | A lean or rich fuel injector, refer to Fuel Injector Diagnosis

• | An engine mechanical condition, refer to Symptoms - Engine Mechanical

### Repair Instructions

• | Ignition Coil Replacement

• | 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 60 s.
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.