Long-Term Fuel Trim

Long-Term Fuel Trim (Global & Spot Adaptation) occurs while the vehicle is being driven within a specific load and RPM window. As an example of Long-term Adaptation, it might become necessary to increase injector times slightly under all operating conditions to compensate for a line pressure regulator which is slightly below specification at all manifold pressures. This corrective factor will be stored in memory so that the ECM won't have to relearn how to cope with this problem every time you start the car.

Theory of Diagnostic Operation, Long Term Fuel Trim
A long-term fuel trim DTCs will be recorded, freeze frame data stored and the MIL requested on a TRIONIC vehicle when, on two occasions, the fuel system attempts to store a global correction factor for all points in it's memory which exceed it's maximum or minimum limits (<-100% or >+100%).

Long-Term Fuel Trim Enabling Criteria
The long-term fuel trim diagnostic will run when:
^ The key is on

Hardware Required
No additional hardware is needed for either of the fuel trim diagnostics.

Concerns
The Diagnostics for heated oxygen sensors, coolant temperature sensors, catalyst monitoring, etc are all for individual components. In contrast, the fuel trim diagnostic is for an entire system which is made up of many components. It is important to remember that a fuel trim DTC may be triggered by any one of a very long list of possible faults. Always take time to collect and evaluate all available information such as other stored DTCs, driveability complaints, etc. when troubleshooting a fuel trim fault.