P0303

P0303-CYLINDER 3 MISFIRE

For a complete wiring diagram refer to Diagrams/Electrical.

- 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 1 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.

Diagnostic Test

1. DTC IS ACTIVE

Diagnose 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 INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

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

Turn the ignition off.

Disconnect the Ignition Coil harness connector.

Disconnect the No.3 Fuel Injector harness connector.

Ignition on, engine not running.

With a scan tool, actuate the ASD Relay.

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 can result in personal injury or death.

Turn the ignition off.

Connect the Ignition coil harness connector.

Remove the Ignition wire/coil from the Cylinder 3 Spark Plug.

Leave the Fuel Injector harness connector of the cylinder being tested disconnected.

Install a spark tester on the Ignition wire.

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 14

NOTE: Connect the Fuel Injector harness connector before continuing.

5. SPARK PLUG

Turn the ignition off.

Remove the Spark Plug.

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: 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.

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 personal injury or death.

Install a fuel pressure gauge to the fuel rail.

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 12

Above Specification

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

7. FUEL PRESSURE LEAK DOWN

NOTE: Before continuing visually and physically inspect the fuel delivery system for external leaks or damage. Repair/replace as necessary.

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 personal injury or death

Turn the ignition off.

Install special tool #6539 (5/16 inch) or #6631 (3/8 inch) fuel line adapter.

Install the fuel pressure gauge.

Start the engine and allow the fuel system to reach maximum pressure.

Turn the ignition off.

NOTE: Fuel specification is 407 kPa ± 34 kPa (59 psi ± 5 psi).

Using special tool #C4390, Hose Clamp Pliers, pinch the rubber fuel line between the fuel pressure gauge and the engine.

Monitor the fuel pressure gauge for a minimum of 5 minutes.

NOTE: The pressure should not fall below 241 kPa (35 psi).

Does the pressure fall below the listed specification?

Yes

- Replace the leaking Fuel Injector(s).
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 8

8. FUEL INJECTOR OPERATION

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 personal injury or death.

CAUTION: After each Fuel Injector actuation, start the engine to clean the cylinder of fuel. Failure to do so could cause engine damage.

Remove special tool #C4390.

Start the engine and allow the fuel pressure to reach maximum pressure.

Ignition on, engine not running.

Using a scan tool, actuate the No.3 Fuel Injector.

Monitor the fuel pressure gauge.

Does the fuel pressure gauge indicate a drop in fuel pressure?

Yes

- Go To 9

No

- Go To 10

NOTE: Turn the ignition off, remove the Fuel Pressure gauge, and connect the fuel lines before continuing.

9. ENGINE MECHANICAL

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

10. FUEL INJECTOR

Turn the ignition off.

Disconnect the No.3 Fuel Injector harness connector.

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.

With the scan tool, erase DTCs.

Install an Injector Noid light.

With the scan tool, actuate the Fuel Injector.

Does the Noid light blink/flicker during the actuation?

Yes

- Replace the Fuel Injector.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 11

11. (K13) INJECTOR 3 CONTROL CIRCUIT

Turn the ignition off.

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 Miller Special Tool #8815 to perform diagnosis.

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

12. 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 personal injury or death.

Turn the ignition off.

Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.

Install special tool #6539 (5/16 inch) #6631(3/8 inch) fuel line adapter and the fuel pressure gauge between the fuel supply line and the fuel pump module.

Ignition on, engine not running.

With a 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 13

13. 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 personal injury or death.

Turn the ignition off.

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

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 can result in personal injury or death.

Disconnect the No.3 Ignition Coil harness connector.

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.

Crank the engine for 5 seconds while observing the test light.

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

Yes

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

No

- Go To 15

15. (K93) COIL CONTROL 3 CIRCUIT