P0303-MISFIRE DETECTED CYLINDER 3

For a complete wiring diagram Refer to Section 8W

When Monitored:
With the engine running.
Set Condition:
The ECM detects multiple misfires from cylinder 3.

Possible Causes

ENGINE COMPRESSION

FUEL INJECTOR QUANTITY

FUEL SUPPLY CONTAMINATION

INJECTOR LEAKAGE

INTERMITTENT CONDITION

Diagnostic Test

1.CHECK FOR ACTIVE DTC

NOTE: If the ECM detects and stores a DTC, the ECM also stores the engine/vehicle operating conditions under which the DTC was set. Some of these conditions are displayed on the scan tool at the same time the DTC is displayed.

NOTE: Before erasing stored DTCs, record these conditions. Attempting to duplicate these conditions may assist when checking for an active DTC.

Did this DTC set again?

Yes

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Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)

2.FUEL CONTAMINATION

Is the fuel contaminated?

Yes

Refer to the Service Information to remove and replace fuel throughout the fuel system.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

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3.CHECKING THE SUPPLY SIDE FUEL DELIVERY SYSTEM

NOTE: The following is a list of problems that can cause fuel pressure to deviate from specification: restricted fuel filter or fuel lines, air in fuel system, failed fuel sending unit, contaminated fuel.

Were there any problems with the Fuel Delivery System?

Yes

Repair as necessary in accordance with the Service Information.
Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)

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4.ENGINE COMPRESSION

Is the cylinder compression within specification for all cylinders?

Yes

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Repair as necessary in accordance with the Service Information.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

5.FUEL INJECTOR CIRCUIT RESISTANCE

Is the resistance below 10.0 ohms for each measurement?

Yes

Replace the Fuel Injector(s) as necessary.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

Repair the Fuel Injector circuit(s) that measured above 10.0 ohms for an open.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).