P1129 Possible Causes
Crossed HO2S harness connectors (downstream) HO2S wiring crossed at harness connectors (downstream) HO2S wiring crossed at 104-pin harness connectors (downstream)
How to Fix P1129 Code MERCURY?
Start by checking the “possible causes” listed above. Visually inspect the corresponding wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Check Engine Light on (or soon-to-be service engine warning light)
P1129 MERCURY Meaning
The Heated Oxygen Sensor (HO2S) monitor determines whether the HO2S signal response for a fuel change matches the correct engine bank. The test fails when a response from the tested HO2S is not indicated.