Diagnostic Procedure

Refer to ENTERING ON-BOARD DIAGNOSTICS in this article to retrieve fault codes. If no fault codes are present and/or DRB-II (C-4805) is being used, but vehicle still displays one of the following conditions, go to appropriate test.

No start condition or engine will not continue to run after start. Go to No Start Test 1 (NS-1) chart for your engine.
Engine runs but has performance problems. Go to Driveability Test 1 (DR-1) chart for your engine.

NOTE: When using trouble shooting charts for diagnosis, DO NOT skip any steps in chart as incorrect diagnosis will result.

Before proceeding with diagnosis, the following precautions must be followed:

Vehicle must have a fully charged battery and no charging system problems.
When probing connectors, probe connector from pin side. DO NOT backprobe connector.
When performing electrical tests, be careful not to cause any short circuits. This will set more fault codes, making diagnosis of original problem more difficult.
DO NOT use a test light in place of a voltmeter.
When checking for spark, ensure coil wire is no more than 1/4" from ground. If wire is farther away from ground, damage to vehicle electronics may result.
DO NOT prolong testing of fuel injectors as engine may hydrostatically lock.
Always repair lowest fault number (CHECK ENGINE light) or first fault displayed (DRB-II) first.