Short Term Fuel Trim

Short-Term Fuel Trim (Lambda Control) occurs when the pre-catalyst Oxygen sensor voltage has an immediate impact on injection duration during closed loop operation. For example, the ECM might find it necessary to increase injector duration to compensate for the affects of an air leak. Depending on the cause and the severity of the problem it might be necessary to make this correction only under full load or over a broader range of conditions. The TRIONIC system has the ability to change the "normal" injection times by ±25%.

Theory of Diagnostic Operation, Short-Term Fuel Trim
The short-term fuel trim diagnostic runs continuously once it's enabling criteria have been met. The MIL will not be illuminated until the problem has occurred twice anytime within 80 trips. In this respect it is very much like the emissions-related misfire diagnostic discussed earlier. The diagnostic will fail if fuel trim stays locked at it's limits (<-25% or >+25%) for more than 20 seconds.

TRIONIC Short-Term Fuel Trim
Enabling criteria
The short-term fuel trim diagnostic will run when:

^ The engine is running
^ Coolant temperature is above 140 F (60 C)
^ The fuel system is operating in closed loop