579 Insufficient A/C pressure change
How to read it
Code 579 reads as 5 flashes, pause, 7 flashes, pause, 9 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 OBD-I code reading guide walks through the paperclip method, code 12, and reading two-digit codes.
What does Ford code 579 mean?
579. Insufficient A/C pressure change. This code sets when your vehicle computer detects insufficient a/c pressure change.
Common causes of 579
- Wiring
- A/C fault
- A/C pressure sensor
- Variable control relay module
- Wiring to A/C compressor clutch open circuit
- ECM
How to fix 579
- Check the circuit wiring and harness for damage, chafing or a poor splice
- Check for A/C fault
- Test the A/C pressure sensor and replace it only if it fails its own test
- Test the variable control relay module and replace it only if it fails its own test
- Check the circuit wiring for an open circuit
- Test the ECM last, only after every circuit test has passed
- Clear the code, then retest to confirm the fix holds