'Check Engine' Light will not come on
 

Help! 1996 SL320, unmolested, bone stock, well maintained. First year for OBD II inspections in my state.
Took in for inspection at local shop, check engine light does not come on, key on, engine off. (Wife-daily driver- does not recall last time she saw the light on) Will not communicate with his OBDII machine.
Took in to dealer for 60k service and OBD II inspection. Check engine light will NOT come on, will not comunicate with OBD II machine. Dealer's solution is install new Diagnostic Module, $1700 for the part, $200 labor.
I fought the "Battle of the Instrument Cluster" and pulled the cluster(thanks to forum search for instructions), pulled 'check engine' bulb and verified that it is good with meter and by applying 12v to bulb contacts. Checked PC board and twist-in contacts, no problem found. Re-installed cluster, still NO check engine lite when key is switched on, engine not started.
Met with DMV officer today in attempt to have them inspect my car with (pre-96) tailpipe test, may as well have discussed it with my dog. His postion, "no check engine light, No inspection".
Have removed covers at the 38 pin MB diagnostic enclosure and rear section of fusebox, wiggle tested ALL those modules, relays and connectors.

Has anyone run into this before?

Does anyone know exactly which devise, in which enclosure is the "diagnostic module"?

Can I replace the module myself, does it need some kind of programming?

Thanks,
Mike K

Check the fuses in the base module.




Joe

Joe,
Every fuse in main fusebox, including # 35 (base module) fuse, has been checked. Also (2) 10A fuses inside enclosure at 38 pin connector, and at fuse box in trunk. All fuses good.
For some reason there is NO fuse in #34 (ignition coils) but there is voltage supplied to fuse slot. Installing a fuse there affects nothing that I can find, I sure was hoping it would bring on the 'MIL'.
I'm still digging here, open to any suggestions!

Mike K

Mike, check my . . .
 

page (click 'www' house below) for operation of Base Module, Menu #8.

Jim,
What a wealth of information at your website! Thanks for compiling all the data and pointing me to it.

After studying everything I can find, here are my conclusions, someone please correct me where I am wrong:

1)Base Module is in same enclosure (F23?) where the 38 pin diag. connector (X11/4) is, passenger side, near firewall

2)My SL320 (production date 1-10-96) has (2) 10amp fuses in base module, both of which are good.

3)These BM fuses each protect several circuits, appears 1 fuse covers MIL, DM, Fuel pump, and injectors, blown fuse would kill the engine.

4)Diagnostic module is in same enclosure, I _THINK_ its the one in the center, with 2 separate harnesses connected by silver latching mechanisms.

5)Because my car is a late 96 with OBDII, pulling DTC's requires scanner, no need for me to build a DIY LED code reader. At present no DTC's can be accessed due to inoperative 'check engine' lite.

Since my "Check Engine" MIL will NOT come on at ANY time, I am certain the bulb is good, and all fuses are good, stands to reason the DM is not switching it on. This is the same ($2000) conclusion Beck Mercedes came to, even without pulling the cluster and checking the MIL bulb. Is the official Mercedes Benz diagnostic computer that good?

Questions:

According to NCDMV, manufacturer is required to extend warranty (95 and later cars) period of eight years and 80K miles for "specified major emission control components." Beck Mercedes' position is this DM is an 'interface point', not emission related, thus not covered under extnd. warranty.

1)Has anyone on this forum had any success at getting MB to warranty such items?

2)Is there ANY information actually stored on DM, any reason a 'recycled' part couldn't be plugged in?

3)would a recycled DM from any other Mercedes be interchangeable with mine?

Thanks for any input.
Mike K

Mike, glad my page . . .
 

was of some benefit to you: that's why it's there.

At the bottom of the page, click on Part Trackers and put out a request for a USED part. When I had trouble (about three years ago) with the DI Module (Menu #5), I got a replacement (used) from a NYC junk yard for $200. New part is $1100. Still running strong.

1)Has anyone on this forum had any success at getting MB to warranty such items? <--- If your car is "starmarked", you should have no trouble but if not, lots of luck!

2)Is there ANY information actually stored on DM, any reason a 'recycled' part couldn't be plugged in? <--- The DM purpose is to interface with all of the other modules and serve as a central point to read DTCs using the LED/SW combo that was deleted in late 94. With that LED/SW, one (anybody) could quickly read stored codes. My '94 still has one. As I've stated above, a used one (that's good) should fix you up.

3)would a recycled DM from any other Mercedes be interchangeable with mine? <--- yes, if it has the same part number.