Code Definition

P1177 — O2 Correction Behind Catalyst B2 Limit Attained

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Audi

About P1177

P1177 is a manufacturer-specific powertrain diagnostic trouble code recorded for Audi vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1177 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The oxygen sensor mounted behind the catalytic converter monitors catalyst efficiency and also supplies a slow trim correction that fine tunes the closed loop control being run by the upstream sensor, compensating for ageing and drift in that front sensor. DTC P1177, which corresponds to VAG fault 17585, is stored when this rear sensor correction on bank 2 reaches the limit of its authority. The ECM has applied as much offset as it is allowed and the rear sensor is still reporting a mixture that does not match target, so the code is telling you that the front sensor control loop and the real e...

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