178 HO2S switch time is slow (bank no. 1)

How to read it

Code 178 reads as 1 flash, pause, 7 flashes, pause, 8 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.

What does Ford code 178 mean?

178. HO2S switch time is slow (bank no. 1). This code sets when your vehicle computer detects ho2s switch time is slow (bank no. 1).

Common causes of 178

• Intake leak
• Excessive fuel in engine oil
• Fuel pressure
• Fuel filter/pump
• Injectors
• HO2S
• AIR system
• MAF/MAP sensor
• ECM

How to fix 178

1. Check for an intake leak
2. Check for excessive fuel in engine oil
3. Check for fuel pressure
4. Check the fuel filter and the fuel pump delivery
5. Check the injectors for a clogged or a leaking one
6. Test the HO2S and replace it only if it fails its own test
7. Check the AIR system for a stuck valve, a blocked passage or a dead pump
8. Test the MAF/MAP sensor and replace it only if it fails its own test
9. Test the ECM last, only after every circuit test has passed
10. Clear the code, then retest to confirm the fix holds