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: Random/Multiple Cylinder 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 the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, then DTC P0300 sets.

### Conditions for Running the DTC

• | DTC P0010, P0011, P0101, P0102, P0103, P0106, P0108, P0116, P0117, P0118, P0128, P0220, P0315, P0335, P0336, P0341 and P1258 are not set.

• | The engine speed is between 425-6,200 RPM.

• | The ignition voltage is between 9-18 volts.

• | The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).

• | The fuel level is more than 10 percent.

• | The throttle angle is steady, or the throttle angle does not increase or decrease by more than 5 percent.

• | The antilock brake system (ABS) and the traction control system (TCS) are not active.

• | The transmission is not changing gears.

• | The A/C not changing states.

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

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

• | DTC P0300-P0308 runs 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 levels to exceed mandated standards.

DTC P0300 is a type B DTC.

### Conditions for Clearing the MIL/DTC

DTC P0300 is a type B DTC.

### Diagnostic Aids

• | You must perform the CKP System Variation Learn Procedure before proceeding with this diagnostic procedure.

• | This test procedure requires that the vehicle battery has passed a load test and is completely charged.

• | When disconnecting harness connection or removing fuses and relays from a fuse block, always inspect the electrical terminals for corrosion, and for mating terminal tightness.

### 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

#### Scan Tool Reference

Control Module References

### Circuit/System Verification

Important: Excessive vibration from other sources other than the engine could cause a DTC P0300 to set.

• | Variable thickness of the brake rotors, Refer to Symptoms - Hydraulic Brakes .

• | Worn or damage engine accessory drive belt, refer to Drive Belt Rumbling and Vibration Diagnosis .

1. With the engine running, there should be no abnormal engine noise.

⇒ | If abnormal engine noise is detected, then refer to Base Engine Misfire with Abnormal Internal Lower Engine Noises or Base Engine Misfire with Abnormal Valve Train Noise .

2. Diagnose any other DTCs that are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
3. Observe the Misfire Current Counters with a scan tool.
4. The engine Misfire Current Counter should not be incrementing.

⇒ | 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. The other option is to refer to Testing for Intermittent Conditions and Poor Connections .

### Circuit/System Testing

1. Operate the engine within the conditions listed in the Freeze Frame/Failure Records.
2. A current misfire should not be indicated on the scan tool.

⇒ | If a single cylinder Current Misfire is indicated, inspect the following components of the affected cylinder for proper operation:

• | Inspect and verify that the fuel injector wiring harness connection are connected to the proper fuel injectors. Refer to Engine Controls Schematics .

• | The ignition coil, refer to Electronic Ignition (EI) System Diagnosis .

• | The spark plug wire resistance, Refer to Spark Plug Wire Inspection .

• | The spark plugs--Refer to Spark Plug Inspection .

• | The base engine--Refer to Base Engine Misfire without Internal Engine Noises .

• | The base engine--Refer to Base Engine Misfire with Coolant Consumption .

• | The base engine--Refer to Base Engine Misfire with Excessive Oil Consumption .

⇒ | If more than 1 cylinder is randomly misfiring, inspect the following components for proper operation:

• | Inspect and verify that the fuel injector wire harness connection are connected to the proper fuel injectors. Refer to Engine Controls Schematics .

• | The vacuum hoses, seals, and connections--Refer to Electronic Ignition (EI) System Diagnosis .

• | The air cleaner element--Refer to Air Cleaner Element Replacement .

• | The crankcase ventilation system--Refer to Crankcase Ventilation System Inspection/Diagnosis .

• | The spark plugs--Refer to Spark Plug Inspection .

• | The fuel system--Refer to Fuel System Diagnosis .

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

• | The ECM electrical grounds--Refer to Engine Controls Schematics .

• | The throttle body or intake manifold assembly for vacuum leaks, damaged seals or gaskets

• | The base engine--Refer to Base Engine Misfire without Internal Engine Noises .

• | The base engine--Refer to Base Engine Misfire with Coolant Consumption .

• | The base engine--Refer to Base Engine Misfire with Excessive Oil Consumption .

### Repair Verification

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

1. Operate the vehicle at 2,500 RPM for 5 minutes.
2. Operate the vehicle within the Conditions for Running DTCs P0420 or P0430. Refer to DTC P0420 or P0430 . Verify that DTC P0420 or P0430 does not set.

⇒ | If DTC P0420 or P0430 runs and fails, then refer to DTC P0420 or P0430 .

3. Using a scan tool clear all DTCs.
4. Ignition OFF for 1 minute.
5. Start the engine.
6. 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. Verify that DTC P0300-P0308 does not set.

⇒ | If DTC P0300-P0308 fails this ignition cycle a misfire condition still exists.