Diagnostic Aids

Monitor voltage at each QDM terminal while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Fig 1: Code P1640 Schematic (3.4L) QDM "A" Error

Fig 2: Code P1640 Diagnostic Flow Chart (3.4L) QDM "A" Error