Well I attempted the drive cycle shortly after my last post. I had the front O2 sensor replaced the day before. After driving 55mph for 5 minutes and decelerating to 0 without braking, the MIL lamp comes on! This time its the rear O2 sensor. Just had that replaced yesterday. 60miles so far, no luck on the monitors.

Update: Finally took my 96 c280 to the dealership. They determined a new DM was required, costing 1780.00 (parts/labor) and ordered from Germany. The next day, they called me saying they found a used one that installed brought the priced to around 600.00. They installed the used DM and have driven the car for 2 weeks (200miles) and the same 3 monitors are not running. Now they want to order the new DM but I'm reluctant because I'll be out 1780.00 if this doesn't work. They are going to make some calls to see if its some other underlying problem before ordering the new DM.

I see you're on the Benzworld forum, as well. I responded there to your last e-mail there. I'll just cut and paste: If anything, find out how much the ECU costs as that is the one thing I can't test.

That's misinformation. The diagnostic module is not married to the car. The ECU's starting in 1996 were. I know this because I have access to a 1994 C280. I switched out the diagnostic module as the dealer said they thought it was the diag module. Must be their default answer. Anyways, I switched out the diag modules between the 2 cars and the 94 ran all the monitors (with my diag module) while mine ran into the same 3 not completing with the 94 diag module. I also know from technical sources, that it was the ECU's that were coded starting in 1996. Sure enough the 94 ECU in my 96 would not allow the car to start. It may be the ECU but I'm not going to spend several thousand on a module that can't be returned or resold. After 5 starts, a new ECU gets married to the car (really the ECU to the starter module, so if you find the pair I suppose from the junkyard, you could test it.) All I know for sure is, that the secondary air is not running the second time. Does your secondary air run after the car has warmed up? I'm sure MB has a regional technician that knows the in and outs of the OBDII crap they designed. I'm pretty sure I know more than the dealer techs at this point. I know I don't have all the tools, as well. Please keep me updated.

Interesting, I have a 1996 S600 Coupe that I'm having problems getting the EVAP, O2, Heated O2 and AIR monitors to set. The car runs great and the MIL is off. Goes into closed loop. I've driven the car for over 3000 miles since it's acquisition in varying conditions and still the monitors haven't set. I know that AZ has something like TSB (Technical Service Bulletins) for cars that have known issues with having trouble setting the monitors. Could the 1996 Benzs be one of those? I'm wondering if this is common amongst 1996 model year Mercedes US market cars (being the first year for OBD II and all)?

So I'm looking for a solution(s) that others have found.

Anyone have any idea where the Diagnostic Module is on a 1996 W140/C140?

Also interesting that you got 1994 and 1996 Diagnostic Modules to interchange.

Karl

1994, for the most part, is identical to the 1996 (I do see where they began cost cutting on some of the most ridiculous things, ie, trim items which you would think was literally pennies. 1994, being the first year in the US for the W202 model, MB knew OBDII would be in effect by 1996 so they had OBDII in the 94 model. Again, no problem whatsoever having the 94 run all monitors with the 1996 DM. And the same 3 monitors not running on the 96 with the 94 DM. There is something wrong with the logic chain in which, at minimum, the 2ndary air is not running upon closed loop in my car. Of course, upon cutting costs on trim pieces, they did spend engineering dollars to code the ECU's to the Ignition. Genius.

I'm in Orange County - If I come to you could you help me?
Steve 714 362 5479