P0303-CYLINDER 3 MISFIRE
For a complete wiring diagram Refer to Section 8W.
- When Monitored:
Any time the engine is running and the adaptive numerator has been successfully updated.
- Set Condition:
If the PCM detects that the variation in crankshaft speed between each cylinder exceeds a calibrated value, based on engine rpm and load, a fault is set.
| Possible Causes |
| INTERMITTENT DTC |
| FUEL DELIVERY SYSTEM |
| ECT SENSOR, WIRING, OR CONNECTORS |
| MAP SENSOR, WIRING, OR CONNECTORS |
| O2 SENSOR, WIRING, OR CONNECTORS |
| ENGINE MECHANICAL SYSTEM |
| POWERTRAIN CONTROL MODULE (PCM) |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
Diagnostic Test
1. DTC IS ACTIVEDiagnose and repair any other active component or circuit DTCs before continuing with this procedure.
Turn the ignition on.
With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
Start the engine and allow it to reach operating temperature.
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
NOTE: Attempt to operate the vehicle under conditions similar to which the DTC was set.
NOTE: It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set.
With a scan tool, select View DTCs.
Is the status Active for this DTC?
Yes
- Go to 2
No
- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
2. DIAGNOSTIC INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause this DTC to set.
NOTE: When a misfire is detected, the PCM will shut down the injector control circuit for the misfiring cylinder.
Inspect the engine for any of the following conditions:
- Worn serpentine belt
- Misalignment or binding water pump, P/S pump or A/C compressor pulleys
- Improper CKP, CMP, MAP, or TP Sensor mounting.
- Poor connector/terminal to component connection for CKP sensor, CMP sensor, MAP sensor, TP sensor, fuel injector, ignition coil, etc.
- Corroded PCM power or ground circuits.
- Vacuum leaks.
- Restriction in the air induction or exhaust system.
- Internal engine component malfunction.
NOTE: Misfire may occur and may not be caused by component failure. Any of the following conditions can cause a misfire:
- Moisture on ignition system components
- Insufficient fuel
- Low quality fuel
- Manual transmission bog
- Towing overload
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 3
3. CHECKING THE FUEL DELIVERY SYSTEM
Perform the diagnostic procedure for *CHECKING THE FUEL DELIVERY SYSTEM.
Were any problems found?
Yes
- Repair as necessary in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 4
4. CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR OPERATION
Perform the diagnostic procedure for *CHECKING THE ENGINE COOLANT TEMPERATURE SENSOR OPERATION.
Were any problems found?
Yes
- Repair as necessary in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 5
5. CHECKING THE MAP SENSOR OPERATION
Perform the diagnostic procedure for *CHECKING THE MAP SENSOR OPERATION.
Were any problems found?
Yes
- Repair as necessary in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 6
6. CHECKING THE OXYGEN SENSOR OPERATION
Perform the diagnostic procedure for *CHECKING THE OXYGEN SENSOR OPERATION.
Were any problems found?
Yes
- Repair as necessary in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 7
7. CHECKING THE ENGINE MECHANICAL SYSTEM
Perform the diagnostic procedure for *CHECKING THE ENGINE MECHANICAL SYSTEM.
Were any problems found?
Yes
- Repair as necessary in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go to 8
8. POWERTRAIN CONTROL MODULE (PCM)
Using the wiring diagram/schematic as a guide, inspect the wiring and connectors relative to the components tested in this procedure.
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Monitor the scan tool data relative to the components tested in this procedure and wiggle test the wiring and connectors.
Look for the data to change or for a DTC to set during the wiggle test.
Refer to any Technical Service Bulletins that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Replace and program the PCM in accordance with the Service Information.
- Perform the PCM Verification Test. (Refer to 9 - ENGINE - STANDARD PROCEDURE)