If the STFT adjustments reach the set limit, a DTC will be recorded.

• A. True
• B. False
• C. It depends on vehicle
• D. It depends on fault codes

Answer: (B)

Short-term fuel trim adjusts the air-fuel mixture on the fly to keep the engine operating near the target. When the required adjustment pushes the STFT to its maximum or minimum limit, the system can’t compensate further with short-term changes and may rely on long-term fuel trim to continue adapting. A diagnostic trouble code isn’t automatically stored just because STFT hits its limit. DTCs are set by diagnostic monitors only when a fault condition lasts long enough and meets specific thresholds (and often with corroborating signals from other sensors). So simply reaching the STFT limit does not guarantee a DTC; it depends on how the condition persists and how the monitors classify the fault.