Code Definition

P1128 — Oxygen Sensor Signal Too Lean, long term fuel trim

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

About P1128

P1128 is a manufacturer-specific powertrain diagnostic trouble code recorded for Kia vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1128 is stored, the module has detected a sensor-related fault — the reported value from the named sensor is out of spec.

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

On Kia vehicles, the P1128 fault code indicates the Powertrain Control Module (PCM) has added the maximum amount of fuel allowed through short and long term fuel trim, yet the upstream oxygen sensor still reports a persistently lean mixture. The code sets when the PCM reaches its fuel trim correction limit and can no longer bring the air to fuel ratio back to target. A lean reading of this kind is usually caused by unmetered air entering after the mass air flow sensor, an exhaust leak ahead of the sensor, a shortfall in fuel delivery, or a sensor reading incorrectly. When this code is set the ...

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