Code Definition

P1123 — Fuel mixture RICH, long term fuel trim

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

About P1123

P1123 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.

P1123 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) continuously monitors exhaust oxygen content through the upstream heated oxygen sensor and adjusts fuel delivery using short term and long term fuel trim. DTC P1123 is set on Hyundai and Kia vehicles when the long term fuel trim for Bank 1 reaches its maximum negative (subtract fuel) correction because the air fuel mixture is persistently rich. The ECM has been removing as much fuel as its adaptive authority allows, yet the mixture remains richer than the target stoichiometric ratio. Common driveability symptoms include a strong fuel smell from the exhaust, blac...

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