P1631

DTC P1631 PCM/ECM COMM ANTI-THEFT ERROR INCORRECT PASSWORD

Circuit Description
The Immobilizer Control Unit (ICU) produces a theft deterrent signal when the ignition is ON and an authorized ignition key is sensed by the ICU. The powertrain control module (PCM)/engine control module (ECM) monitors this signal during crank. If the proper signal is present on the theft deterrent signal circuit, the PCM/ECM allows the engine to continue to run. If the PCM/ECM detects that the signal is incorrect while the engine is running, DTC P1631 will be set. The PCM/ECM will then discontinue engine operation.

Conditions for Setting the DTC
- The engine is running.
- The PCM/ECM detects an incorrect signal on the theft deterrent fuel enable circuit.
- The above conditions are present for longer than 2 seconds.

Action Taken When the DTC Sets
- The PCM/ECM will not illuminate the Malfunction Indicator Lamp (MIL).
- The PCM/ECM will store conditions which were present when the DTC set as Fail Records data only. This information will not be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC
- A history DTC P1631 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P1631 can be cleared by using the scan tool.

Steps 1 To 12:

Diagnostic Aids
An intermittent may be caused by poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:
- A poor connection in the PCM/ECM and ICU harness and connectors. Check for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- A damaged wiring harness. If the harness appears OK, disconnect the ICU, turn the ignition ON and observe a voltmeter connected to the signal circuit from the PCM/ECM at the ICU harness connector while moving connectors and wiring harnesses related to the theft deterrent system. A change in voltage will indicate the location of the fault.

Reviewing the Fail 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.