Fuel Trim Diagnostics

Amost every driveability diagnostic requires the use of fuel trims. Interpreting fuel trim values is a critical skill for modern day technicians. This class is about creating a diagnostic strategy to solve fuel trim codes and related issues.

The instructor will demonstrate, via case studies, how to interpret and how to use fuel trims when diagnosing driveability concerns. BMW, Chrysler, Ford, GM, Nissan, and Toyota case studies will be presented.

Discuss topics to include:

  • Using the Front O2 Sensor/Air Fuel Sensor and the Rear O2 Sensor to Determine if the Fuel Trims are Accurate
  • How to Separate "Air" Problems From "Fuel" Problems
  • Interpreting the Relationship Between Fuel Trim and the MAF to Determine MAF Accuracy
  • Using Trims to Diagnose Lean Issues Caused by Excessive Alcohol in the Fuel, Restricted Fuel Injectors, and Low Fuel Pressure
  • Using Trims to Diagnose Rich Issues Caused by Leaking Injectors, Leaking High Pressure Fuel Pumps, and Air Mass Over-Estimation Using Fuel Trims

Written by MAACA