172 HO2S system indicates lean
How to read it
Code 172 reads as 1 flash, pause, 7 flashes, pause, 2 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 172 mean?
172. HO2S system indicates lean. This code sets when your vehicle computer detects ho2s system indicates lean.
Common causes of 172
- Vacuum or intake leak
- Low fuel pressure or a clogged fuel filter
- Faulty oxygen sensor
- Open or shorted wiring or a bad connector in the circuit
- Dirty or weak fuel injectors
How to fix 172
- Confirm the code and read the flash sequence again
- Check for vacuum and intake leaks
- Inspect the oxygen sensor and its connector for damage and corrosion
- Measure fuel pressure and check the fuel filter
- Replace the oxygen sensor or a failed part only after the tests