Code : P1129
Description : P1129 MERCURY 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)
Solutions :
– Carry out a Reset via CarDiag
– Choose a better quality fuel
– Check that the tank cap is securely closed
– Check the oil level and add more if it is lower than MAX
– Restart an Automatic diagnostic via CarDiag
– If the fault persists, you can check the “Possible causes” listed above : visually inspect (by yourself (tutorials to come) or by a professional) the wiring harness and the associated connectors, check for damaged components, and look for broken, bent, pushed, or corroded connector pins.

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