P1631Manufacturer-specific code

P1631 Code: Theft Deterrent Start Enable Signal Incorrect (GM)

On General Motors vehicles (Chevrolet, GMC, Buick, Cadillac), the P1631 code means the theft deterrent start enable signal is incorrect. The engine does not start or shuts off, and the security light is on. It often appears after a computer or body module was replaced without programming.

Severity
High
Can I keep driving?
No, stop and have it checked
Estimated cost
$0 to $350
Difficulty
Medium
System
Computer and Outputs
Applies to
Depends on the manufacturer

Common in: Chevrolet

Updated Reviewed by Renzo Chacca

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What the P1631 code means

P1631 is a manufacturer-specific code: the 1 in the second position means each automaker defines what it means, not the generic SAE standard. The most widespread definition is the one used by General Motors (Chevrolet, GMC, Buick, Cadillac). If your vehicle is another brand, confirm the code text with a scan tool that supports that manufacturer.

ManufacturerMeaning of P1631
General Motors (Chevrolet, GMC, Buick, Cadillac)Theft deterrent start enable signal incorrect

The GM theft deterrent system (Passlock or Passkey) checks the key and sends the computer a fuel enable signal.

The computer sets the P1631 code when the theft deterrent signal arrives but with an incorrect password. It shows up after the computer or the body module was replaced without being programmed.

Before you start repairs, confirm the make, model, year and engine. With manufacturer codes, the same number can change even between engines from the same brand.

P1631 code symptoms

  • The engine does not start or shuts off.
  • Security light on.

Likely causes of the P1631 code

  1. Computer or module replaced without programming. This is uncommon, so rule out everything else first.
  2. Key not recognized. Confirm it with the tests in the diagnosis section.
  3. Communication. Confirm it with the tests in the diagnosis section.

How to diagnose the P1631 code step by step

  1. Find out whether any part was replaced recently.
  2. Perform the relearn.

How to fix the P1631 code

  • Program the computer or perform the relearn.

Technical reference data

  • It requires a relearn with a scan tool or a timed procedure.
  • P1xxx codes are manufacturer-specific: confirm the definition with a scan tool that supports your brand.
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

If a computer or body module was swapped before the problem began, that is almost certainly the answer. Start with the relearn.

P1631 on GM

Common on Chevrolet, GMC, Buick, Pontiac and Cadillac vehicles.

If your vehicle is another brand, check the table above for the meaning its manufacturer gives this code and confirm it with a compatible scan tool.

Frequently asked questions about P1631

What does the P1631 code mean on a GM?
It means the theft deterrent start enable signal is incorrect. The engine does not start or shuts off, and the security light is on.
Does P1631 mean the same thing on every brand?
No. It is a manufacturer-specific code, so on other brands it may not exist or may mean something different. Confirm it with a scan tool that supports your make.
Can I drive with a P1631 code?
Not until it is resolved. With a P1631 code the engine may not start or may shut off.
How much does it cost to fix P1631?
Roughly $0 to $350 on a GM. A relearn can cost nothing, while programming a replacement module costs more.
Will a P1631 code clear itself?
No. The password mismatch stays until the computer or module is programmed or the relearn is completed.
What is the most common cause of P1631?
A computer or body module that was replaced without programming. An unrecognized key and a communication fault come next.

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Questions about the P1631 code

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