Understanding OBD DTC P1629: The Theft Deterrent System Trouble Code

Understanding OBD DTC P1629: The Theft Deterrent System Trouble Code

If you’ve encountered the P1629 diagnostic trouble code (DTC) in your vehicle, you’re likely dealing with an issue related to your car’s theft deterrent system. This blog post will dive deep into what P1629 means, which vehicles are commonly affected, and how to diagnose and fix the problem. Let’s get started!

What is the P1629 Code?

P1629 is a manufacturer-specific diagnostic trouble code that generally refers to a problem with the vehicle’s theft deterrent system. Specifically, it indicates that the Powertrain Control Module (PCM) is not receiving the correct fuel enable signal from the Body Control Module (BCM) or the Vehicle Theft Deterrent (VTD) module.

The official definition may vary slightly depending on the vehicle manufacturer, but it’s commonly described as:

  • “Theft Deterrent Fuel Enable Signal Not Received”
  • “Theft Deterrent Crank Signal Malfunction”

Top 20 Vehicles Commonly Affected by P1629

While this list is not exhaustive, the following vehicles are known to frequently experience the P1629 code:

  • Chevrolet Cavalier
  • Pontiac Grand Am
  • Buick LeSabre
  • Cadillac CTS
  • Chevrolet Malibu
  • GMC Sierra
  • Pontiac Grand Prix
  • Oldsmobile Alero
  • Saturn Vue
  • Chevrolet Impala
  • Buick Century
  • Pontiac Sunfire
  • Chevrolet Silverado
  • GMC Yukon
  • Cadillac STS
  • Buick Regal
  • Chevrolet Monte Carlo
  • Pontiac Bonneville
  • Oldsmobile Intrigue
  • Saturn Ion

Implications on Vehicle Performance and Emissions

The P1629 code primarily affects the vehicle’s starting and running capabilities. Here are the main implications:

  • No-start condition: In many cases, the engine may crank but fail to start or start briefly and then stall.
  • Intermittent stalling: Some vehicles may experience intermittent stalling while driving.
  • Security light activation: The security or theft system warning light on the dashboard may illuminate or flash.
  • Fuel system disruption: The PCM may not pulse the fuel injectors, effectively disabling the vehicle.
  • Emissions impact: While not directly related to emissions, a non-running or poorly running engine can indirectly affect emissions if the issue persists.

Diagnosing and Fixing P1629

Key Symptoms:

  • Engine cranks but doesn’t start
  • Engine starts briefly then stalls
  • Security light flashing or illuminated
  • Intermittent stalling while driving

Diagnostic Steps:

  1. Use an OBD-II scanner to confirm the P1629 code and check for any additional codes.
  2. Inspect all relevant fuses, particularly those related to the BCM, ECM, and theft deterrent system.
  3. Check the battery voltage and ensure it’s at least 12.6 volts.
  4. Examine wiring and connectors between the BCM, PCM, and theft deterrent module for damage or corrosion.
  5. Verify the proper operation of the ignition switch and key.

Potential Solutions:

  • Replace faulty fuses
  • Repair or replace damaged wiring or connectors
  • Perform a relearn procedure for the theft deterrent system (may require a professional scan tool)
  • Replace the Vehicle Theft Deterrent (VTD) module if faulty
  • In some cases, the PCM may need reprogramming or replacement

Frequently Asked Questions

Q: Is it safe to drive with the P1629 code?
A: If your vehicle starts and runs, it’s generally safe for short distances. However, the risk of stalling makes it unsafe for regular driving. It’s best to address the issue promptly.

Q: How much does it cost to fix P1629?
A: Costs can vary widely depending on the root cause. Simple fixes like fuse replacement might cost under $100, while more complex issues involving module replacement or reprogramming could range from $300 to $1000 or more.

Q: Can I fix P1629 myself?
A: Some aspects, like checking fuses and inspecting wiring, can be done at home. However, system relearns and module programming typically require professional equipment and expertise.

Q: How can I prevent P1629 from occurring?
A: Regular maintenance, avoiding electrical system modifications, and using the correct key are the best preventive measures. Also, address any electrical issues promptly to prevent cascading problems.


The P1629 code, while not directly related to engine performance or emissions, can significantly impact your vehicle’s operation. Prompt diagnosis and repair are crucial to ensure your car starts reliably and runs efficiently. If you’re uncomfortable with electrical diagnostics, it’s best to consult a professional mechanic who can accurately diagnose and resolve the issue. Remember, maintaining your vehicle’s theft deterrent system is not just about convenience—it’s an important aspect of your car’s overall security and functionality.

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