Code Definition

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

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

About P1166

P1166 is a manufacturer-specific powertrain diagnostic trouble code recorded for Volkswagen 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) stores its learned mixture corrections in more than one long term fuel trim block, so that the idle and low load region and the part load and higher load region can be adapted separately. Trim block 1 is the low load or additive correction and trim block 2 is the load dependent or multiplicative correction, which is applied as a percentage of the calculated injector opening time across the load range. DTC P1166 is set when the second long term fuel trim block for bank 1 reaches the rich correction limit, meaning the ECM is multiplying the injector opening time b...

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