Diagnostic Aids

Check for any of the following conditions:

• Check resistance of main relay. Resistance across terminals No. 3 and No. 5 is 79-95 ohms at 68°F (20°C). Resistance across terminals No. 1 and No. 2 is infinite.
• Main relay electrical contacts may be pitted or sticking. Replace main relay if tapping gently on relay, or wiggling relay causes a change in relays operation.
• Performance of main relay may be affected by temperature. Check main relay after vehicle has sat outside overnight and after running engine 30 minutes
• Check for a faulty electrical connection to PCM.
• An intermittent malfunction may be caused by a fault in main relay electrical circuit. Inspect wiring harness and components for an intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.