If the STFT adjustments reach the set limit, a DTC sets.

• A. True
• B. False
• C. It causes limp mode
• D. It has no effect

Answer: (B)

Short-Term Fuel Trim (STFT) is the quick, real-time adjustment the engine control module makes to keep the air-fuel ratio near the target based on the oxygen sensor signal. It has upper and lower limits, and when those limits are reached, the system can’t compensate further with fast corrections. However, a diagnostic trouble code for fueling isn’t triggered just because STFT hits its limit. DTCs related to fueling are typically set only after Long-Term Fuel Trim (LTFT) has been out of range for a sustained period, often across multiple drive cycles. So, reaching the STFT limit signals a problem but does not by itself cause a DTC to be stored; persistent out-of-range LTFT or other fault conditions are what drive a DTC.