How do I fix Ford code 631?

Check the fuse and the bulb for that circuit Check the circuit wiring and harness for damage, chafing or a poor splice Test the ECM last, only after every circuit test has passed Clear the code, then retest to confirm the fix holds

631 Transmission control indicator lamp circuit failure KOEO

Q: What does Ford code 631 mean?

Ford code 631. Transmission control indicator lamp circuit failure KOEO. Applies to 1981-1995 Ford, Lincoln and Mercury EEC-IV vehicles.

Make: Ford (1981-1995)
Category: Powertrain - Transmission
Severity: Check Engine Light
Applies to: 1981-1995 Ford, Lincoln and Mercury EEC-IV vehicles

How to read it

Code 631 reads as 6 flashes, pause, 3 flashes, pause, 1 flash on the check-engine light. Jumper the self-test input to signal return at the test connector, then run the key on engine off self test and the running self test, counting the check-engine flashes each time.

New to flash codes? The OBD-I code reading guide walks through the paperclip method, code 12, and reading two-digit codes.

What does Ford code 631 mean?

631. Transmission control indicator lamp circuit failure KOEO. This code sets when your vehicle computer detects transmission control indicator lamp circuit failure koeo.

Common causes of 631

Bulb
Wiring
Fuse
ECM

How to fix 631

Check the fuse and the bulb for that circuit
Check the circuit wiring and harness for damage, chafing or a poor splice
Test the ECM last, only after every circuit test has passed
Clear the code, then retest to confirm the fix holds