P0303

P0303-CYLINDER 3 MISFIRE

For a complete wiring diagram, refer to the Wiring Information.

- When Monitored:
Any time the engine is running and the adaptive numerator has been successfully updated.

- Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes one soft fail to set a malfunction and two trips to set the MIL. Three good trips to turn off the MIL.

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. DTC IS ACTIVE
1. Diagnose and repair any other active component or circuit DTCs before continuing with this procedure.
2. Turn the ignition on.
3. With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
4. 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 may result in possible serious or fatal injury.

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.

5. With the scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. . Intermittent Condition Test

2. VISUAL 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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 3

3. (F342), (F344) ASD RELAY OUTPUT CIRCUIT

NOTE: Diagnose any ASD related DTCs before continuing.

1. Turn the ignition off.

NOTE: The 3.7L V6 engine uses a modified Distributorless Ignition System (DIS) with coil consolidation on the left side engine bank.

2. Turn the ignition off.
3. Disconnect the Ignition Coil harness connector.
4. Disconnect the No.3 Fuel Injector harness connector.
5. Ignition on, engine not running.

6. With the scan tool, actuate the ASD Relay.
7. Using a 12-volt test light connected to ground, probe the (F342), (F344) ASD Relay Output circuit in the Ignition Coil harness connector and Fuel Injector harness connector while the ASD Relay is actuating.

Does the test light illuminate brightly?

Yes

- Go To 4

No

- Repair the excessive resistance or short to ground in the (F342), (F344) ASD Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. IGNITION SYSTEM OPERATION

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 may result in possible serious or fatal injury.

1. Turn the ignition off.
2. Connect the Ignition coil harness connector.
3. Remove the Ignition wire/coil from the Cylinder 3 Spark Plug.
4. Leave the Fuel Injector harness connector of the cylinder being tested disconnected.
5. Install a spark tester on the Ignition wire.
6. While cranking the engine observe the spark coming from the spark tester.

NOTE: A crisp blue spark that is able to jump the gap of the spark tester should be generated.

Is good spark present?

Yes

- Go To 5

No

- Go To 13 NOTE: Connect the Fuel Injector harness connector before continuing.

5. SPARK PLUG
1. Turn the ignition off.
2. Remove the Spark Plug.
3. Inspect the Spark Plug for the following conditions:
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broken electrode

NOTE: Lightly tap the bottom of the spark plug on a solid surface. The electrode in the spark plug should not move.

Were any of the above conditions present?

Yes

- Replace the Spark Plug.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 6

6. FUEL PRESSURE CHECK

WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in possible serious or fatal injury.

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 may result in possible serious or fatal injury.

1. Install Fuel Pressure Decay Tester 8978 to the fuel rail.
2. Start the engine and observe the fuel pressure reading.

NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Choose a conclusion that best matches your fuel pressure reading.

Within Specification

- Go To 7

Below Specification

- Go To 11

Above Specification

- Replace the fuel filter/pressure regulator.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

7. FUEL PRESSURE LEAK DOWN
1. Perform the Fuel Pressure Leak Down Test. . Fuel Pressure Leak Down

Were any repairs made after performing the leak down test?

Yes

- Testing complete.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

8. ENGINE MECHANICAL
1. Check for any of the following conditions/mechanical problems:
- ENGINE VACUUM - must be at least 13 inches in neutral
- ENGINE VALVE TIMING - must be within specifications
- ENGINE COMPRESSION - must be within specifications
- ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks
- ENGINE PCV SYSTEM - must flow freely
- TORQUE CONVERTER STALL SPEED - must be within specifications
- POWER BRAKE BOOSTER - no internal vacuum leaks
- FUEL - must be free of contamination
- CAM LOBES - must not be worn excessively
- CYLINDER LEAKAGE TEST - must be within specifications
- VALVE SPRINGS - cannot be weak or broken

Are there any engine mechanical problems?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 16

9. FUEL INJECTOR
1. Turn the ignition off.
2. Disconnect the No.3 Fuel Injector harness connector.
3. Ignition on, engine not running.

NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.

4. With the scan tool, erase DTCs.
5. Install an Injector Noid light.
6. With the scan tool, actuate the Fuel Injector.

Does the Noid light blink/flicker during the actuation?

Yes

- Verify that there is good pin to terminal contact in the related Injector and the Powertrain Control Module connectors. If OK, replace the Fuel Injector.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 10

10. (K13) INJECTOR 3 CONTROL CIRCUIT

1. Turn the ignition off.
2. Disconnect the C2 PCM harness connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install PCM Pinout Box 8815 to perform diagnosis.

3. Check the (K13) Injector 3 Control circuit for an open, short to ground and short to voltage.

Was a problem found with the (K13) Injector 3 Control circuit?

Yes

- Repair the excessive resistance or short in the (K13) Injector 3 Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 16

11. FUEL SUPPLY LINE RESTRICTED

WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in possible serious or fatal injury.

1. Turn the ignition off.
2. Raise the vehicle on a hoist and disconnect the fuel pressure line at the fuel pump module.
3. Install the Fuel Pressure Decay Tester 8978 between the fuel supply line and the fuel pump module.
4. Ignition on, engine not running.
5. With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Is the fuel pressure within specification?

Yes

- Repair or replace fuel supply line as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 12

12. FUEL PUMP INLET STRAINER

WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in possible serious or fatal injury.

1. Turn the ignition off.
2. Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.

Is the Fuel Inlet Strainer plugged?

Yes

- Replace the Fuel Pump Inlet Strainer.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Before continuing, check the Fuel Pump Module harness connector terminals for corrosion, damage or terminal push out. Make sure the ground circuit is functional. Repair as necessary. Replace the Fuel Pump Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

13. IGNITION WIRE

NOTE: If the vehicle or the cylinder being tested does not have an ignition wire answer YES to this test and continue.

1. Turn the ignition off.
2. Remove the ignition wire.
3. Measure the resistance of the ignition wire.

Is the resistance below 10K Ohms?

Yes

- Go To 14

No

- Replace the Ignition Wire.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

14. IGNITION COIL

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 may result in possible serious or fatal injury.

NOTE: The 3.7L V6 engine uses a modified Distributorless Ignition System (DIS) with coil consolidation on the left side engine bank.

1. Disconnect the No.3 Ignition Coil harness connector.
2. Using a 12-volt test light connected to 12-volts, probe the (K93) Coil Control 3 circuit.

NOTE: Make sure the test light is probing the circuit before actuating the Coil or a DTC may set and not allow the actuation.

3. Crank the engine for five seconds while observing the test light.

Does the test light brightly blink/flicker while the engine is cranking?

Yes

- Verify that there is good pin to terminal contact in the related Coil and the Powertrain Control Module connectors. If OK, replace the Ignition Coil.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 15

15. (K93) COIL CONTROL 3 CIRCUIT