P0631: VIN Not Programmed or Incompatible TCM

P0631 is the transmission module counterpart of P0630: the transmission control module holds no VIN, an invalid one, or one that does not match the vehicle – usually compared with the VIN of the engine or body module. Typical is a replaced transmission module or mechatronic unit (on dual-clutch and automatic gearboxes with integrated control) that was not VIN-programmed, or a used part. Depending on the architecture the transmission module itself or the engine module sets the code. No manufacturer table or bulletin available to us names P0631; the description follows CARB's VIN rules and the documented P0630 procedure (Hyundai, Ford), where the VIN is distributed to all modules that need it and stored once. Shifting is usually normal, but adaptations or configuration may be blocked.

Medium severity. Can I keep driving?It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

Symptoms

Check engine light or transmission warning
Scan tool shows no or a wrong VIN in the transmission module
Transmission adaptation possibly impossible
Driving often normal

Most likely causes

Transmission module or mechatronic unit replaced, VIN not written
Used transmission module from another vehicle
Interrupted transmission module programming
CAN communication fault during the VIN comparison

What to check, in order

Start with the simplest. You can tick off each step.

Check the battery and grounds
Clear the code and see if it returns
If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
Check whether a software update is available
Do not replace the control module without a full diagnosis

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P0631 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
6: Control modules and outputs
31: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0631?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0631?

The most common causes are: transmission module or mechatronic unit replaced, VIN not written; used transmission module from another vehicle; interrupted transmission module programming.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.