Diagnostic Aids

Check for the following conditions:

• Poor connection at PCM: inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
• Damaged harness: inspect the wiring harness for damage, If the harness appears to be okay, disconnect the PCM, turn the ignition ON and observe a voltmeter connected to the suspect driver circuit at the PCM harness connector while moving connectors and wiring harnesses related to the MIL. A change in voltage will indicate the location of the fault.
• Poor connection at component: examine for damaged connectors, unplugged connector, or damaged terminals at the following locations: Instrument cluster harness, canister purge solenoid, A/C clutch relay. An open ignition feed circuit at any of these components will cause DTC P1640 to be set

Reviewing the FAILURE RECORDS vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.