621 Shift solenoid 1 circuit failure KOEO
How to read it
Code 621 reads as 6 flashes, pause, 2 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 621 mean?
621. Shift solenoid 1 circuit failure KOEO. This code sets when your vehicle computer detects shift solenoid 1 circuit failure koeo.
Common causes of 621
- ATF level/condition
- TCC slipping
- ECM
How to fix 621
- Check the transmission fluid level and condition, and look for slip under load
- Test the ECM last, only after every circuit test has passed
- Clear the code, then retest to confirm the fix holds