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: 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 P0016, P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0335, P0336, P0340, 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 torque management is not active.

• | The fuel tank level is more than 12 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.

• | The transmission is not changing gears.

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

• | 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

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

#### Special Tools Required

J 26792 Spark Tester

### Circuit/System Verification

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

1. Engine idling 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. Verify the following DTCs are not set: P0201, P0202, P0203, P0204, P0315, P0335, P0336, P0351, or P0352 are not set.

⇒ | If a DTC is 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 Misfire Current Counters, with a scan tool. The Misfire Current Counters should not be incrementing.
4. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### 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

• | 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 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 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 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:

• | Gas, coolant, or oil fouled

• | 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 idling, with a scan tool, observe the misfire counters and see if the misfire follows the spark plug that corresponds to the misfiring cylinder.

⇒ | 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 Verification

1. If the customer concern was a flashing MIL, operate the vehicle within the conditions for running the 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.