What does P1631 mean on a Chevy?

P1631. Theft Deterrent Start Enable Signal Not Correct. Applies to Silverado, Sierra, Impala, Malibu, Cavalier.

What causes P1631 on a Chevy?

Incorrect Passlock sensor voltage from a worn ignition lock cylinder Faulty theft deterrent module sending an invalid start-enable password Damaged exciter ring or magnet around the ignition cylinder Wiring fault in the start-enable signal circuit between VTD module and PCM

How do I fix P1631 on a Chevy?

Measure Passlock sensor voltage in each key position and compare to specifications Perform the Passlock relearn procedure with a fully charged battery Inspect the ignition cylinder and exciter components for wear or damage Use a Tech2/GDS2 scan tool to verify the start-enable password exchange during cranking

Code

P1631

Theft Deterrent Start Enable Signal Not Correct

Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: Silverado, Sierra, Impala, Malibu, Cavalier
Related: No single generic twin. See OBD Codes List

What it means

P1631. Theft Deterrent Start Enable Signal Not Correct. This Chevy-enhanced code applies to Silverado, Sierra, Impala, Malibu, Cavalier.

Findings, check these first

Incorrect Passlock sensor voltage from a worn ignition lock cylinder
Faulty theft deterrent module sending an invalid start-enable password
Damaged exciter ring or magnet around the ignition cylinder
Wiring fault in the start-enable signal circuit between VTD module and PCM

Standard procedure

Measure Passlock sensor voltage in each key position and compare to specifications
Perform the Passlock relearn procedure with a fully charged battery
Inspect the ignition cylinder and exciter components for wear or damage
Use a Tech2/GDS2 scan tool to verify the start-enable password exchange during cranking

Look up another code

Press / to jump to the box. Chevy-enhanced powertrain, body, chassis and network codes.

Sources and review

Review: no source links are recorded for this entry.

Last updated 2026-09-13.

Report a correction for P1631. Include your vehicle, the issue and a source if you have one.

This fault sits in the GM theft deterrent system. The GM security codes and Passlock relearn guide covers the families and the relearn cycles.