Code Definition

P1166 — Long term fuel trim 2 bank 1 above rich limit

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

About P1166

P1166 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.

When P1166 is stored, the module has detected a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine.

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.

P1166 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 Engine Control Module (ECM) uses the upstream oxygen sensor to hold the air fuel ratio at stoichiometric, applying a short term correction and storing the learned average of that correction as long term fuel trim. On these VAG applications the long term trim is learned in separate ranges, and Range 2 is the multiplicative correction learned in the part load and higher airflow region rather than at idle. DTC P1166 is stored when the long term fuel trim for bank 1 in that part load range reaches its maximum permitted limit in the fuel removing direction, because the mixture is genuinely too ...

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