Replacement or second-hand TCM that has not been programmed with the vehicle's VIN; TCM software or calibration update that was interrupted or failed to write the VIN; VIN mismatch between the TCM and the engine control module or other modules, for example after a module swap; Corrupted TCM memory caused by a low battery voltage event or power interruption during programming; Network communication fault, wiring or connector problem preventing the TCM reading the VIN from other modules; Internal TCM fault, including a faulty mechatronic or integrated gearbox control unit on models that use one.

P0631

VIN Not Programmed or Incompatible - TCM.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
31: FaultThe specific fault in that area

What it means

P0631 is a generic powertrain code meaning the transmission control module (TCM) has found that the vehicle identification number (VIN) is missing, not programmed or does not match what it expects. The TCM compares its stored VIN with the one held by other modules on the network, and sets the code when the check fails. It is most often seen after a TCM has been replaced or reprogrammed, or when software has been updated incorrectly.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Transmission stuck in a single gear or limp-home mode
Harsh, delayed or erratic gear changes
Gearbox will not shift out of park or neutral on some models
Reduced engine power or torque limitation
Other stored communication or transmission codes alongside P0631

Possible causes

Replacement or second-hand TCM that has not been programmed with the vehicle's VINlikely
TCM software or calibration update that was interrupted or failed to write the VINlikely
VIN mismatch between the TCM and the engine control module or other modules, for example after a module swappossible
Corrupted TCM memory caused by a low battery voltage event or power interruption during programmingpossible
Network communication fault, wiring or connector problem preventing the TCM reading the VIN from other modulespossible
Internal TCM fault, including a faulty mechatronic or integrated gearbox control unit on models that use onerare

How to diagnose

Read all stored codes and freeze frame data, and note whether any network or communication codes are present with P0631
Check the vehicle history for recent TCM, engine control module or battery replacement, or any software update
Compare the VIN stored in the TCM with the VIN on the vehicle and in the other modules using a suitable diagnostic scan tool
Check battery condition and charging voltage, as low voltage can corrupt module memory
Inspect TCM wiring, connectors and earths for damage, corrosion or water ingress
Check the network for faults and confirm the TCM communicates with the other modules
Check for any manufacturer service information or software updates that apply to the specific model and gearbox
Clear the code after any repair and road test to confirm it does not return

How to fix

Program or learn the correct VIN into the TCM using the manufacturer-approved procedure for the model
Reprogram the TCM with the correct, up-to-date software and calibration if the earlier update failed or is outdated
Correct the VIN in any other module that holds a mismatching VIN
Repair damaged wiring, connectors or earths and any network faults found
Replace the TCM if it cannot be programmed or has an internal fault, then program it to the vehicle

Can I keep driving?

Medium severity

The car can usually be driven short distances, but the gearbox may be in limp mode with limited gears and poor shifting. Get it programmed soon, as continued driving in limp mode is inconvenient and may be unsafe in traffic.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.