Ford 51 Engine coolant temperature circuit open
How to read it
Code 51 reads as 5 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 How to Read Ford EEC-IV Self-Test Codes walks through the test and what the numbers mean. The general OBD-I guide covers the rest.
What does Ford code 51 mean?
Engine coolant temperature circuit open
Common causes of 51
- Wiring open circuit
- ECT sensor
- ECM
How to fix 51
- Check the circuit wiring for an open circuit
- Test the ECT sensor and replace it only if it fails its own test
- Test the ECM last, only after every circuit test has passed
- Clear the code, then retest to confirm the fix holds
Source
Source review recorded
Sources and review
Review: checked against the recorded source material.
- EEC-IV Ford trouble code table (MIL, description, type)
archived reference page (troublecodes.net via Wayback Machine)
Supports: code identity and meaning
Fetched directly. Code row matches the description used in the data file.
https://web.archive.org/web/20030720231430id_/http://www.troublecodes.net:80/Ford/eec-iv.shtml
- Ford EEC-IV trouble codes, Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995 (code, fault location, probable cause)
archived reference page (troublecodes.net via Wayback Machine)
Supports: code identity and probable causes
Independent table on the same archive site with matching code identity and additional probable causes.
https://web.archive.org/web/20160502051413id_/http://www.troublecodes.net:80/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/
- Ford EEC-IV trouble code table: code, fault location, probable cause (Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995)
reference page (troublecodes.net)
Supports: per-code probable causes used for the page cause list and test order
Fetched 2026-09-30. The probable cause column is what the page lists, in source order, with the test order built from it.
https://www.troublecodes.net/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/
Last updated 2026-09-29.
Report a correction for 51. Include your vehicle, the issue and a source if you have one.