P1631 on Chevrolet
Theft Deterrent Start Enable Signal Not Correct
P1631 on Chevrolet vehicles indicates theft deterrent start enable signal not correct. Au7o has documented this code across 1 Chevrolet model — most commonly on Impala. This is a manufacturer-specific (primarily GM) security code meaning the engine control module did not receive a correct 'start enable' signal or password from the vehicle's theft-deterrent / immobilizer system. The anti-theft system requires the ECM and the theft-deterrent module to exchange a matching coded handshake before the engine is allowed to run; if that signal is missing or doesn't match, the ECM blocks fueling and the engine may crank but not start. It generally indicates a communication or authentication breakdown in the immobilizer system rather than a mechanical engine fault, and is often accompanied by a lit security light. Typical repair costs on Chevrolet range from $150 to $600, depending on the specific model and root cause.
Common Causes of P1631
- •Faulty or unprogrammed ignition key, key fob, or transponder
- •Worn or faulty ignition lock cylinder / key reader
- •Theft-deterrent module (passlock/immobilizer) fault
- •Damaged wiring or connectors between the BCM/TDM and ECM
- •Body control module fault
- •Module needing relearn after a battery, key, or part change
- •Signal interference from a second key on the ring or tampering
P1631 on Chevrolet by Model
Chevrolet Impala(1 issue)
- Passlock Security System No-Start Condition2000-2005
The Passlock anti-theft system causes intermittent no-start conditions where the security light flashes and the fuel pump is disabled. The ignition lock cylinder contains a Hall-effect sensor that reads a resistance value; when contacts wear or corrode, the BCM detects a mismatch and locks out fuel delivery. The problem typically worsens progressively from occasional to daily. 225+ complaints were filed for the 2002 model year alone.
Looking for P1631 on a different make?
View P1631 across all makes →Frequently Asked Questions
What does P1631 mean on Chevrolet?▼
P1631 stands for "Theft Deterrent Start Enable Signal Not Correct." This is a manufacturer-specific (primarily GM) security code meaning the engine control module did not receive a correct 'start enable' signal or password from the vehicle's theft-deterrent / immobilizer system. The anti-theft system requires the ECM and the theft-deterrent module to exchange a matching coded handshake before the engine is allowed to run; if that signal is missing or doesn't match, the ECM blocks fueling and the engine may crank but not start. It generally indicates a communication or authentication breakdown in the immobilizer system rather than a mechanical engine fault, and is often accompanied by a lit security light. On Chevrolet specifically, this code is documented across 1 model.
What causes P1631 on Chevrolet vehicles?▼
Common causes on Chevrolet: Faulty or unprogrammed ignition key, key fob, or transponder, Worn or faulty ignition lock cylinder / key reader, Theft-deterrent module (passlock/immobilizer) fault, Damaged wiring or connectors between the BCM/TDM and ECM, Body control module fault. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P1631 on a Chevrolet?▼
Repair costs on Chevrolet range from $150 to $600, depending on the specific model and root cause.
Which Chevrolet models have P1631 documented?▼
Au7o has documented P1631 on 1 Chevrolet model: Impala.