Code Definition

P1138 — Long Term Fuel Trim Add. Fuel B2 System Too Lean

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

About P1138

P1138 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.

P1138 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) corrects fuel delivery using two learned long term fuel trim values, a multiplicative correction that dominates at higher engine speeds and an additive correction that dominates at idle and low load where intake vacuum is highest. DTC P1138 is set when the additive long term fuel trim for Bank 2 reaches a positive limit because the ECM is continually adding fuel at idle to compensate for a lean condition. Bank 2 is the cylinder bank that does not contain cylinder number one, and because the additive value reflects low airflow operation this code points strongly ...

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