P1123–P1125 Long Term Fuel Trim, Additive Air, Bank 1 - System too Rich
The engine is getting more fuel than it can burn for the air coming in - a leaking injector, high fuel pressure or a lazy oxygen sensor.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P1123 | Long Term Fuel Trim, Additive Air, Bank 1 - System too Rich | Investigate soon |
P1125 | Long Term Fuel Trim, Additive Air, Bank 2 - System too Rich | Investigate soon |
The definition
P1123: Long Term Fuel Trim, Additive Air, Bank 1 - System too Rich.
P1123 is a manufacturer-specific powertrain code (the engine or gearbox). Its meaning is set by the carmaker rather than by the SAE standard, so a generic OBD-II reader will often show it as an unknown code or misread it.
What to check first
Cheapest and fastest checks first:
- Check fuel pressure against spec, and look for a leaking injector.
- Check whether the oxygen sensor is lazy rather than dead - a slow sensor drives the mixture rich without setting its own fault.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P1123 mean?
P1123 means Long Term Fuel Trim, Additive Air, Bank 1 - System too Rich. The engine is getting more fuel than it can burn for the air coming in - a leaking injector, high fuel pressure or a lazy oxygen sensor.
Can I drive with P1123?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.