If a long-term fuel trim (LTFT) reading of -30 exists, what could be the implication?

A long-term fuel trim (LTFT) reading of -30 indicates that the engine control module (ECM) is significantly reducing the amount of fuel being injected. This usually happens when the ECM senses that there is too much fuel in the mixture, leading to a lean condition. In this case, if LTFT is -30, it suggests the ECM is trying to compensate for an excessively rich mixture by cutting back on fuel delivery.

The correct implication of a -30 LTFT is that there may be an issue with fuel management, which aligns closely with the idea of a potential failure in the fuel control monitor. This failure might manifest as an inability to accurately modify fuel delivery to achieve the desired air-fuel ratio.

Additionally, while a faulty oxygen sensor could contribute to this reading by providing incorrect feedback to the ECM, the option indicates a specific failure in the fuel control system rather than just a sensor issue. The reading of -30 is less indicative of normal operation or simply a condition caused by a vacuum leak, both of which would not typically produce such an extreme LTFT value.

In summary, the presence of a -30 LTFT suggests significant intervention by the ECM, which points to possible failures within the fuel control logic or management system