1997 Mercury Cougar Service Engine Soon Light

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DTC P1131 Lack of HO2S-11 Switch, Sensor Indicates Lean.

This trouble code is most commonly known for indicating a failed heated oxygen sensor. Your vehicle uses 4 oxygen sensors. Although this code indicates oxygen sensor 1, bank 1. It is wise to replace all at once as they are part of regular maintenance and the others will fail soon otherwise. All of the oxygen sensors on located on the exhaust system. Two being near lower rear of engine in the exhaust manifold while the other two are at the rear of the engine in the exhaust piping.