P1631 - FAULT CODE - OBD2

POST UPDATED IN February, 2023

P1631 Code failures by brands

P1631 BUICK, CADILLAC, CHEVROLET, GMC: IMMOBILIZER FUEL ACTIVATION SIGNAL IS NOT CORRECT.

Description of DTC code P1631

The immobilizer belongs to your vehicle’s security system, it avoids the engine starts unless the transponder key is present. When the key is inserted into the ignition switch, this transmits an electronic code to the vehicle. The engine will only start if the smart key fob matches the immobilizer code.

The BCM (Body Control Module) often communicates with the ECM (Engine Control Module) by sending a security code through a serial data circuit. After this, the ECM sends a challenge to the BCM. Both controllers make some calculations on this challenge. If the calculated response of the BCM is equal to the calculation performed by the ECM, the vehicle may start.

The P1631 OBDII diagnostic code setting occurs when the security code received by the Engine Control Module from the Body Control Module is wrong.

Symptoms of fault code P1631

Causes of OBD2 P1631

Reasons to set the P1631 OBD2 fault code:

  • The BCM or ECM may have damage to its cables or connectors.
  • The immobilizer may be defective.
  • The ECM may be in bad condition.

Possible solutions of the DTC code P1631

To troubleshoot DTC P1631 OBDII, try this:

  • Considering the normal system settings between the BCM and ECM, any immobilizer B-codes should be diagnosed before P-codes.
  • Perform the immobilizer relearn procedure. The ECM must work properly with the relearn password and get the vehicle to start. Otherwise, there are faults in the ECM.

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