593 Heated oxygen sensor heater circuit malfunction
How to read it
Code 593 reads as 5 flashes, pause, 9 flashes, pause, 3 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 593 mean?
593. Heated oxygen sensor heater circuit malfunction. This code sets when your vehicle computer detects heated oxygen sensor heater circuit malfunction.
Common causes of 593
- Wiring
- HO2S heater relay
- HO2S
- ECM
How to fix 593
- Check the circuit wiring and harness for damage, chafing or a poor splice
- Test the HO2S heater relay and replace it only if it fails its own test
- Test the HO2S 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