P0303

Cylinder 3 Misfire Detected:

Cylinder 3 Misfire Detected (continued):

Ignition System:

Circuit Description

The Powertrain Control Module (PCM) uses the Crankshaft Position (CKP) sensor and the 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 Running the DTC

^ Engine coolant temperature greater than -10°C (14°F).

^ Intake air temperature is between -10°C (14°F) and 50°C (122°F).

^ Barometric pressure greater than 75 kPa.

^ Engine speed less than 4500 RPM.

^ Fuel tank level greater than 25%.

Conditions for Setting the DTC

^ RPM change is less than 200/50 msec.

^ Manifold Absolute Pressure (MAP) change is less than 1.3 kPa/16 firing events.

^ 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 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 consecutively passing cycles without a fault present.

^ A History 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 PCM battery feed.

Diagnostic Aids

Check The Following Conditions:

^ Engine overheating.

^ Vacuum leaks from the air intake system.

^ PCV valve.

^ EGR system.

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

^ Fuel pressure out of specification or a malfunctioning fuel injector.

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

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

^ Damaged harness. Inspect the wiring hamess for damage.

Due to the potentially destructive nature that engine misfire has on the exhaust catalyst always check for proper catalytic convener operation after a misfire has been repaired. This can be accomplished by driving the vehicle at a steady state between 55 to 65 km/h (35 to 45 mph) for 5 minutes. Connect the scan tool and observe the "System Status" "Catalyst" is completed to a "Y" (yes) state, and no DTC set.

If DTC P0303 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set. Also, if the fault can not be duplicated, wet the secondary ignition system and operate the vehicle under the conditions that the DTC set.

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 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.

3. Determine if fault is present. A misfire DTC can be caused by a rough road condition.

8. There are some additional Ignition system functional checks (noise suppressor filter and Ignition Control Module [Igniter]).

11. Low engine compression and improper lash may also cause a rough idling condition.