P0303

DTC P0303 Cylinder 3 Misfire Detected (1 Of 3):

DTC P0303 Cylinder 3 Misfire Detected (2 Of 3):

DTC P0303 Cylinder 3 Misfire Detected (3 Of 3):

Engine Misfire:

CIRCUIT DESCRIPTION

The Engine Control Module (ECM) 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. If the misfire rate is high enough the driving conditions can cause catalytic converter overheating, the MIL will blink.


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%.

- Throttle Position (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 ECM will blink the Malfunction indicator Lamp (MIL) the first time catalytic converter damage has occurred.

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

- The ECM will store vehicle operating conditions which were present when the DTC set in 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.

- DTC(s) can be cleared by using a scan tool or by disconnecting the ECM battery feed.


DIAGNOSTIC AIDS


Check the following conditions:

- If DTC(s) other than Misfire are present (P0300 to P0304) diagnosis those DTC(s) first.

- Engine overheating.

- Vacuum leaks from the air intake system.

- PCV valve. Do a functional check of the PCV valve.

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

- Fuel pressure out of specification or for a malfunctioning fuel injector(s).

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

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

- Damaged harness. Inspect the wiring harness for damage.

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

- If DTC P0303 is intermittent, refer to Symptoms. Testing and Inspection

If DTC P0303 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining 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.


TEST DESCRIPTION


Number(s) below refer to the step number(s) on the Diagnostic Table.


1. The Engine 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. Verifies whether the misfire is present.

3. Verifies whether the misfire is caused by a hard failure or an intermittent. Misfire can sometimes be cause by a rough road condition.

11. Contaminants in the fuel, such as alcohol or water, can create a misfire condition.

22. Low engine compression and improper lash may also cause a rough idling condition. Refer to Engine Mechanical section for additional checks.