P1631 on 2000-2005 Chevrolet Impala — Theft Deterrent Start Enable Signal Not Correct
1 vehicles · 1 makes · $150-$600 repair
Most Reported On
P1631 is an OBD-II diagnostic trouble code meaning “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. This code is most commonly reported on 2000-2005 Chevrolet Impala, with repair costs ranging from $150 to $600.
Common Causes
Typical Repair Cost
Based on 1 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P1631, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
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FAQ
What does P1631 mean?
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.
What are the most common causes of P1631?
The most common causes of P1631 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P1631?
Repair costs for P1631 range from $150 to $600, depending on the vehicle and root cause.
Which vehicles are affected by P1631?
Au7o has documented P1631 across 1 vehicle models from 1 manufacturers: Chevrolet.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.