I have a 94 E320 58000 miles. The vehicle operates flawlessly. Smooth idle, 22 MPG fuel ecnomy, no problems in starting, engine temperature stays between 80 and 95. Everything works fine, except the Check Engine Light. I always get DTC 19 code a few days after resetting and along with it either 3 or 4.

Arther and Suginami are helping me. I have the following checks planned. Pin 8 and see why code 19 is coming up. I will also check the fuel pressure regulator and try to clean the EGR Tube and see what happens.

Enigne Gasket, Aux fans, EGR valve and wiring harness have been replaced. 60000 mile service has also been done, new spark plugs, air, fuel filter, transmission etc.

Mercedes Benz dealer diagnosed my problem as follows:
Function Test W/HHT/ HFM Codes 035 O2 Sensor
Stop/Mixture to lean, 051 Self Adapt too rich, Replace O2 sensor still at Rich stop, Replaced Mass Air still reads flat, Replace over voltage relay, reading still flat, Diag Faulty HFM Control Module $2200.

If anyone else has any idea's or similar past experiences, please let me know. Steve and Jim seem to be the experts on the Bosch Control Modules on this site. I did notice that the LH-SFI module had some software issues.




94 E420 Check Engine Light On

ATTN TECHS