P1129 FORD Downstream Oxygen Sensors Swapped from Bank to Bank

Possible causes

Crossed HO2S harness connectors (downstream)
Crossed HO2S wiring at the harness connectors (downstream)
Crossed HO2S wiring at the 104-pin harness connectors (downstream)

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1129 FORD OBD Code Description

The heated oxygen sensor (HO2S) monitor determines if the HO2S signal response for a fuel shift corresponds to the correct engine bank. The test fails when a response from the HO2S being tested is not indicated.

FORD Related P1129 code