Code Definition

P1128 — Long Term Fuel Trim B1 System Too Lean

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

About P1128

P1128 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.

P1128 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) trims fuel delivery to hold the air to fuel ratio at the correct value, and long term fuel trim is the learned correction it stores over time. DTC P1128 is set when the long term fuel trim for Bank 1 reaches a positive correction limit because the ECM is continually adding fuel to compensate for a lean running condition across the entire speed and load range. A lean mixture means the engine is drawing in more air than is being metered or is not receiving enough fuel, which the oxygen sensor reports back as a persistently lean exhaust. When this code is stored th...

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