What is the normal range for fuel trim data?

[DiEmily]

Fuel trim data should normally fall within the range of -25% to +25%. Below are relevant details: 1. Key indicator: The vehicle's fuel trim value is a crucial parameter for ensuring power performance and fuel efficiency. The ECU receives signals from the intake airflow sensor, air-fuel ratio sensor, and oxygen sensor, then adjusts fuel supply based on current load conditions. Short-term fuel trim values constantly fluctuate with load changes, while long-term fuel trim generally remains inactive. It only intervenes during high-power operations, throttle opening exceeding limits, gear shifts, or sudden load changes. If the long-term fuel trim value keeps changing and the variation magnitude increases progressively, it indicates potential vehicle malfunction. It's recommended to first inspect the catalytic converter. 2. Below 0%: If significantly below 0% (a negative value), it indicates an overly rich system condition, requiring fuel reduction (decreasing injector pulse width). If notably above 0% (a positive value), it suggests a lean condition, prompting the PCM to increase fuel quantity (increasing injector pulse width) for compensation.