Code Definition

P1128 — Fuel mixture LEAN, long term fuel trim

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

About P1128

P1128 is a manufacturer-specific powertrain diagnostic trouble code recorded for Hyundai 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 Powertrain Control Module (PCM) corrects fuel delivery from oxygen sensor feedback, applying an additive trim at idle and a multiplicative trim across the higher load and speed range. DTC P1128 is set on Hyundai and Kia vehicles when the long term multiplicative fuel trim for Bank 1 reaches its maximum positive (add fuel) limit under moderate to high engine load because the air fuel mixture is persistently lean. Because the code sets away from idle, it points strongly at a fuel delivery shortfall that appears when fuel demand is high, or at an airflow metering error that grows with load. D...

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