Steps in Isolating the Problem

• Use Test Modules.
• Perform electrical tests with the DISplus Measurement System or a DVOM.
• Consult fault charts in Repair or Diagnostic Procedures Manuals.
• Control Module Self Diagnosis.
• Use appropriate special tools (e.g. battery draw tester, tank leakage adapters, breakout boxes, etc.).
• Substitute a known good part.

Workshop Hint 

If a TEST PLAN  is not  available:

• Think about the system in its entirety.
• Be sure the normal operation is understood.
• Develop a PLAN.
• Use all available resources.
• Don't try to diagnose the entire system at once, break it into manageable chunks.
• Check the easy things first. It would waste time to install the breakout boxes to find a bad bulb.

If a TEST PLAN is available: 

• Do not skip steps.
• Never assume results without doing a step.
• Recheck your work.