What is the normal range for long-term fuel trim?

[VivienneFitz]

Long-term fuel trim is considered normal within the range of -23% to +16%. If the long-term fuel adjustment value exceeds 5%, it indicates a fault in the engine system. If it is significantly below 0% (a negative value), it signifies an overly rich system condition, and fuel supply should be reduced. The normal operation of a car's engine relies on the fuel supply system. During engine operation, the ECU controls the fuel injection time of the injectors, thereby regulating the fuel injection quantity. Factors affecting the long-term fuel trim coefficient include engine misfires, poor exhaust flow, low fuel pump pressure, or clogged fuel injectors. If the combined value of long-term and short-term fuel trim exceeds 5%, it is considered slightly high. In such cases, you can check for clogged injectors, eroded spark plugs, poor fuel quality, faulty air flow meters, or overdue fuel filter replacement.