Ford 556 Fuel pump relay primary circuit failure
How to read it
Code 556 reads as 5 flashes, pause, 5 flashes, pause, 6 flashes 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 556 mean?
Fuel pump relay primary circuit failure
Common causes of 556
- IFS switch
- Wiring
- Fuel pump relay
- Constant control relay module
- ECM
How to fix 556
- Test the IFS switch and replace it only if it fails its own test
- Check the circuit wiring and harness for damage, chafing or a poor splice
- Check the fuel filter and the fuel pump delivery
- Test the constant control relay module 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
Qualified source review
Sources and review
Review: qualified. Read the source limits below.
- EEC-IV Ford trouble code table (MIL, description, type)
archived reference page (troublecodes.net via Wayback Machine)
Supports: code identity and meaning
Fetched directly. The three-digit 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 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 556. Include your vehicle, the issue and a source if you have one.