DFI System Check: Notes

The DFI SYSTEM CHECK is an organized approach for identifying a problem caused by DFI system. Driver comments normally fall into one of the following: steady "SERVICE NOW/SOON" lights, driveability problems, engine will not start, or engine stalls after start.

1. Lighting of "SERVICE NOW/SOON" lights during cranking confirms battery and ignition voltage to ECM.
2. If engine control system light is on with engine running, check for ECM codes. Diagnose all codes before proceeding with DFI SYSTEM CHECK.
3. After codes are corrected, ability of DFI system to control fuel delivery to engine must be checked.
4. Check for proper closed/open loop operation.
5. If closed loop is achieved, fuel system has to be checked for rich, lean or proper fuel control. The DFI system has ECM data code "ED19" integrator. This monitors oxygen sensor rich/lean status and drives fuel system richer if oxygen sensor is lean. Also, it drives fuel system leaner if sensor is rich.