I am in process of tearing car apart to resolve problem. Maybe someone has some ideas? I carry a remote starter to start car. It starts immediately and runs beautifuly but 90% of the time I have to use remote starter. No matter what I do with the shifter, it doesn't make any difference. I have cleaned the grounds(all of them). I hook up a multimeter and turning the ignition switch is not sending any voltage to starter. The remote starter I hook to two posts on back of starter which provides current (directly from battery) to starter solenoid which kicks off engine immediately once I push start button on remote.
Sometimes its a little tricky hooking up my alligator clips because of engine heat. I am thinking that it is not the neutral safety switch because I move shift lever to neutral which I thought bypasses neutral safety switch. I am looking for a start relay which shows up in a schematic of wiring. I checked all relays in the trunk on right side above the battery. Battery is located in right wheel well. This is a 1993 w140 300SD diesel. I believe there is another relay in the start circuit which is under the dashboard somewhere. I haven't located it yet. Next I plan to remove covers under the dash and search for any other relays that may cause problem. The starter always cranks with the remote starter cable. Amazingly everything else works on the car. It would be a wonderful car if I didn't have to raise the hood to start it all the time. Any help would be appreciated.

MBdiesel,

Hope this isn't a hijack and has some relevance to your issue. I am dancing around a similar -maybe same - problem on my car ( a 93 300SD). In very hot weather - above 95* - I turn the ignition key and sometimes only the airbag light comes on. No other idiot lights, no starter crank, nothing. This happened last year in our annual NC heatwave. The stealer wanted about $1000 to replace the ignition switch assembly. I passed at that offer and bought another car.

The weather cooled and for most of last year I drove it occassionaly when I had a local round trip and would not shut it off until I got back home. I was 100% successful in having it start. This year the annual heat wave hits again, again no start. The weather has just cooled off and I am again learning to "trust" it.

Is this similar to your conditions or do your idiot lights come on and just no cranking? This seems to be the next project on this car. Then back to determining if the turbo rebuilt significantly helped the oil consumption problem... but that is another post.

Chuck

Thanks for reply. All the dash lights come on, but starter does not crank on final 1/4 turn of key. Cold or hot doesn't matter. The car is apart right now and few weeks will have chance to get it back together. Get yourself a remote starter. Two alligator clips to back of starter and I bet car cranks up immediately. This way you will not get stuck. I am going to try to fix problem . I know I could permanently hard wire with a pushbutton switch to dash to start, but I will try to fix it the correct way. I have replaced ignition switches before and $1000 sounds high. Check all your fuses and relays.
The dealers are always insanely expensive. I would not own 3 Mercedes if I had to go to the dealer for all repairs. I have been working on Benzes for over 30 years. Try to find a local MB mechanic and get a diagnostic check from them. Also there are OBD codes that may indicate problem. The engine harness cable on these cars are biodegradable, check to see that yours is ok. I replaced mine myself, cost me about $300 for cable and took me about 45 minutes for installation. Very easy job. If you need instruction just let me know. Will get back with you about any progress as soon as I get time to finish putting things back in my w140 1993 300SD diesel. I like working on these cars when I have the time.

Chuck , make sure all grounds are good. There are ground wires under the car and in the engine compartment. Disconnect and clean with some light sandpaper and tighten, alot of the relays close on ground contact which is very important to having electric circuit run properly. I am not sure if a faulty
engine harness will keep car from starting, but it probably will not run correctly if there are shorts. Environmental controls etc. might be messed up.
Good Luck Dave

Thanks for the ideas folks. The issue - at least at the moment - seems very closely tied to temperature. 20% of the time when the temp is above 95* outside, it seems that the ignition switch just doesn't make a connection. Turn the key and none of the idiot lights except the air bag one come on. In some of these failures it will work after 10 or 15 retries. Sometimes it will not, and I've wiggled and moved the key for 30 minutes with no results. Next morning when the temp is cooler all is fine. The weather dropped 20* in NC and over the past 3 days I've taken 10 or so trips and it always started. I'll pick up that remote starter and keep it around as a just in case. That may get me home one time until I get it fixed.

The dealer actually saw the problem when I brought it there last year. They seemed to think the whole ignition assembly needed replacing. I don't believe just the tumbler is replaceable on this car. I'm sure they use a shotgun approach since it's not their $. They quoted about $400-500 in parts and then the rest in labor.

There used to be a video on a Texas forum on how to get into the dash and replace this switch on the 140's. I searched here for the link, found it, but the video is not there on that site. I'll keep looking. I don't mind wrenching a bit, but these 140's are a bit tricky for me. All the hidden trim pieces are a real pain to decode.

Any luck on your car yet? It sounds as if it is starter circuit specific for your car.

Also, where did you get your engine harness cables. That is on the list to do also.

Chuck

I purchased harness cable about year ago from parts place called the
Finish line located in Miami. 800-842-7851 ask for Jose , his email is
josef@fnishlin.com. Price may have gone up since I purchases as I know
the dollar keeps getting weaker. I would like to get the link to the Texas location for
ignition switch removal incase I have to repair it.

I know this is an old thread, but I might have a hint. This weekend I got in my 1995 S350D (W140) and it simply would not crank. No click, nothing. The glow plug relay worked as normal, but absolutely nothing happened when I turned the key to the start position. I tried Neutral and park several times. I tried getting a jump start. A good samaratin noticed that the fuse in the number 16 spot was blown. The tag reads 'cigar lighter, glove box light, and anti-theft relay.' The fuse to the anti-theft relay was blown and the car thought it was being stolen.... Quick change of a 10 amp fuse later and I was back in business.

Your remote start set up may be bypassing a faulty anti-theft relay allowing it to start remotely just fine.

Just a thought.

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

I may be a little late but this sounds identical to a similar problem I just had on a 96 SL500 which has I believe the same ignition switch as your car. Only the SRS light would come on, but the starter would crank endlessly, but the engine wouldn't engage. The ignition switch itself was the problem, the black 12, 14 or 16 pin electrical portion of the steering lock assembly behind the tumbler is probably at fault.

__________________


1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

John,

I'm still not convinced it is the ignition switch. In failure mode I get nothing at "on" or "start", only the airbag light. No cranking, no radio, no other idiot lights, nothing. I leave the switch in "on" and use a remote starter ( wire from power to the starter solenoid ) and it will start. There is a light show for about 5 seconds with idiot lights going off and on, then all is fine.... It will start the next time and maybe the next 30 times. See the attached picture for what the dash looks like at "on" and "start".

I think it is harness related in the engine compartment or possibly a bad relay somewhere. The remote starter switch has always started it and the issue clears in a few seconds. I have not taken the time to clean the ground connections as suggested above, but for the last 8 months and 15,000 miles I have had no failures while in cooler weather. The heat is coming though.... I need to finally come up with an engine fix plan and include the harness it that. Anyone know how many harnesses are under the hood?

Chuck

Attached Thumbnails