P0300

Diagnostic Chart:

CKP & Starter Signal:

PCM Ignition System:

Circuit Description

The Powertrain Control Module (PCM) uses the Crankshaft Position (CKP) sensor and Camshaft Position (CMP) sensor to monitor changes in crankshaft rotation for each cylinder to determine a misfire. When the misfire rate equals or exceeds the count indicating that the engine condition has deteriorated, the Malfunction Indicator Lamp (MIL) illuminates. Certain driving conditions can cause the catalytic converter to overheat if the misfire rate is high enough. The MIL will blink when conditions for catalytic converter overheating are present.

Conditions for Setting the DTC

- Engine coolant temperature greater than -7°C (19°F).

- Intake air temperature less than -7° C (19° F).

- Barometric pressure greater than 75 kPa.

- Engine speed less than 4000 RPM.

- Fuel tank level greater than 15%.

- TP sensor change is less than 1 degree /10 msec

- Conditions present for 5 seconds after engine start to 1 second from fuel shut-off.

Action Taken When the DTC Sets

- The PCM will blink the Malfunction Indicator Lamp (MIL) the first time catalytic converter damage has occurred.

- The PCM will illuminate the MIL the second time emission thresholds are exceeded.

- The PCM will store the vehicle operating conditions which were present when the DTC set in the Freeze Frame data.

Conditions for Clearing the MIL/DTC

- The MIL will turn off after three consecutive drive cycles without a fault present.

- A DTC will clear after 40 consecutive warm-up cycles without a fault.

- The DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for any of the following conditions:

If any DTCs other than Misfire are present, P0300 to P0304, diagnose those DTCs first.

- Engine overheating.

- Vacuum leaks.

- Improper EGR system operation.

- A functional check of the PCV valve. Refer to Positive Crankcase Ventilation (PCV) system.

- An ignition system malfunction (spark plug(s), Ignition wire(s), Ignition coil, and the distributor).

- Fuel pressure out of specification. Refer to Table-A-7B for fuel pressure diagnosis. Table A-7B Fuel System Diagnosis (Fuel Pressure Check)

- Check for a malfunctioning fuel injector(s). Normal fuel injector resistance is 12 - 17 ohms at 20°C (68°F). Perform the Fuel Injector Coil Test/Balance Test Procedure if fuel injector resistance is out of specification. Refer to Fuel Injector Coil Test/Fuel Injector Balance Test Procedures. Fuel Injector Balance Test

- An engine mechanical malfunction (engine compression out of specification, valve lash adjuster malfunction).

- A poor connection at the PCM. Inspect harness connectors for a backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

- A damaged wiring harness. Inspect the wiring harness for damage and repair as necessary.

- An intermittent misfire can also be the result of a defective crankshaft timing belt pulley. Remove the crankshaft sensor and look at the crankshaft signal rotor through the sensor hole. Check the crankshaft timing belt pulley for foreign material or damaged teeth.

- If the DTC P0300 is intermittent, Refer to Symptoms. Testing and Inspection
If the DTC P0300 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions since the DTC was last set. This may assist in determining how often the DTC sets.

If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams/Electrical.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The Powertrain (OBD) System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step verifies whether the misfire is present.

3. This step verifies whether the misfire is caused by a hard failure or an intermittent. A misfire can sometimes be caused by a rough road condition.

8. This step checks for the proper clearance of the signal rotor. The signal rotor should have enough clearance to not contact other components when rotating. Signal rotor clearance is not adjustable. A damaged or improperly aligned signal rotor will require component parts replacement. Refer to Ignition System.

11. Checks for contaminants in the fuel, such as alcohol or water, can create a misfire condition. Refer to Fuel for procedures to check for fuel contamination.

22. Low engine compression and improper lash may also cause a rough idling condition. Refer to Engine.