DTC EFI-231

2-3-1 LONG-TERM FUEL TRIM PART LOAD





Trouble Code Conditions
- The engine control module (ECM) receives information from the heated oxygen sensor (HO2S) about the fuel/air mixture in the idling and partial load ranges. If the fuel/air mixture deviates the short-term fuel trim will compensate for this by adjusting injection time.
- When the short-term fuel trim makes an adjustment, the integrator median must be adjusted by the long-term trim. If adaptation needs to adjust to close to its maximum diagnostic trouble code (DTC) EFI-232 (idling range -0.48 ms - +0.40 ms) or diagnostic trouble code EFI-231 (part load range factor 0.773 - 1.227) and the status message Upper limit (lean fuel/air mixture) or Lower limit (rich fuel/air mixture) will be stored.

Substitute value(s)
- None.

Possible source(s)
Upper limit
- Defective mass air flow (MAF) sensor.
- Low fuel pressure.
- Air leakage.
- Faulty sensor signals.

Lower limit:
- Defective mass air flow sensor.
- High fuel pressure.
- Leaking injectors.
- Leaking evaporative emission (EVAP) system.
- Contaminated engine oil.
- Oil level too high.
- Faulty sensor signals.

Fault symptom(s)
- Can result in high fuel consumption.
- May result in poor performance.