I have a 2004 Mercedes-Benz c320 4Matic. Not the flex-fuel version just the regular engine.

Okay, so I'm having random issues where my car won't start. I turn the key and get nothing. When it starts randomly while going down the road I lose my speedometer, transmission stops shifting, etc. Transmission will stay in the top gear when it goes out until slowing down when it downshifts it won't shift up again. Then when turning it off it won't start again and also won't go into gear stuck in park. Then a day or two after I get in and it starts up with no problem again. wtf????

I had an issue before where the battery would be dead if I didn't drive the car in 3-4 days and somehow that fixed itself. Recently I took a trip for the weekend and the car wasn't started for 3 days and the battery started the car with no issues.

I researched and researched for weeks now trying to find out what could be causing this and someone said ECM because at some point when it wouldn't start I tried to scan it and it had no signal to the ECM. So I liked to never found the ECM since there is literally no information for my exact car online. Every guide I found online said the ECM was in a different location than mine was. Mine was in the fusebox panel near the master cylinder. I pulled it out and opened it up to make sure it didn't show any signs of damage and no water damage. It was bone dry and looked pretty much brand new inside. Nothing burn the whole board looked new.

I also checked all the fuses in the entire car. The underhood fusebox, the one on the side of the dash, and the trunk panel. All the fuses are good.

So I researched again for a couple more days.

I thought I had it two days ago. I researched the brake switch and every symptom that I had said the failure of a brake switch so I cheered and ordered a new one from amazon that said it matched my car. Then I get it in today and find out that my car doesn't even have a brake switch! I looked for 30 minutes straight under the dash and nothing. Apparently, it has a brake booster diaphragm under the master cylinder so I researched and researched what all issues if it goes out and I can't find much of anything about the diaphragm. I'm stuck and don't know where to go from here.

I could use some expert help. I'm a do it yourself type of guy. I don't like taking my vehicles to anyone. I've read on a couple of forums to take it and have it STAR scanned and if that's the last resort I'll give that some thought but I'm hoping someone can point me in a direction with some DIY info.

I also want to mention I have no information on anything that has ever been done to this car. I got lucky as hell and traded an old small pickup for it. The guy wanted to create a sleeper with an LS engine in it so he was willing to trade me this car square up for the truck since it was his only vehicle. It was NOT taken care of at all. It had malfunctions out the *** on the dash. Mostly things that don't matter at the moment. Brakes need to be changed, blinker light on the passenger side is busted, needed oil change which I've already done.

It also has a p0400 code which leads to the EGR from what I've researched but I haven't gotten around to trying to fix that yet because the car keeps breaking down on me! I love this car is the most fun car I've ever owned I'll do whatever it takes to fix it so I can keep it and remain driving it. I love the car so much I doubt I'll get rid of it and even with all these problems normally I'd try to sell it as junk by now because I can't stand troublesome cars but this car is something special so I need to keep it.

Update: So this morning once again I get into the car try to start and I get nothing. So I kept trying by pulling the key back out of the ignition and then pushing the brake pedal and putting the key back in and trying it. After about 6-7 tries it actually started up. I don't know what that actually means but it seems like important info to share.

 

Tell me something, is the car getting rained on alot?
Because I've had issues like that with water getting in the car
after a big storm, and after drying out for several days it
miraculously comes back to life.

 

Yes after the huge storm that hit Houston texas not long ago passed through was when the majority of this started happening. It was sitting on the road and the road flooded just a little but it wasn't too bad. Not enough for me to say oh I need to move my car. It must have been enough to get into the starter or something at the bottom of the car. The day after the storm I couldn't get it to do anything, the second day after the storm the starter would click loud over and over again but nothing. The third day it started but since then it has still been doing it which was over a week ago. I figured it was something that just needed to dry out myself because it happened right after that big *** storm with three days of rain but it been over a week and it's still causing issues so I figured it had to be something else. I kind of forgot to mention the storm and what happened after the storm. I've been so aggravated by it all that the rain slipped my mind.

 

No not the starter. Water getting in...messing with the CANBUS.
I had this, and then my mechanic said later he had bunch of car towed in after a big storm.
Mine crapped out, and took 4 days to dry out.
Has happened twice now. Won't start or only runs in limp mode, lights on, no controls working,
stays in 2nd gear etc..

So pull up the carpet, look for any water, change the angle the car is parked so trapped water can run out, check for
blocked water drains (near wipers) . Check the fuse boxes, are they sealed? Water in them?
Just like a dealer to forget to snap down the snaps under the hood.

Next storm, if it's parked outside, put a tarp from the sunroof and covering the trunk.

Last time this happened, it all came back little by little after a week, thankfully except for the instrument panel.,
I heard about a place near me Palo Alto speedometer who could service these things.
I was afraid the mileage in it would be bunged up, and then you can't transfer the data to
replacement ($350 btw) and yer stuck with it saying 999,999 on the dash.
I wrote a thread on this some years back if you care to search for it.

Anyway, they were able to read the mileage and whatever they did woke the damn thing up,
and I didn't end up needing to replace it. And so everything was back to normal.
DON"T DRIVE IT. If you do have to replace the Instrument panel and the mileage in the
panel doesn't match the other components in the car that store this,
ie the transmission and I forget, ecu(?) it goes 999,999 from now on.
If the mileage can't be read it will need a dealer to fix it.

Whats an ECM anyway? What component are you referring to?

 

I pulled the carpet up on both sides of the car under the dash when I was looking for the ECM and I didn't spot any type of water in the floorboards or anywhere under the dash. I did notice a couple of the tubes under the wipers area that were stopped up with leaves and I plan on cleaning them tomorrow. I just noticed them earlier. The side that it is clogged upon is the battery side (passenger side) The only thing on that side is the cover that goes over the battery which has a seal on it that closes in the airbox for the ac etc. I spun the fan around a few times and it was free no water inside. I checked the fusebox also on the opposite side and it was bone dry so as far as I know, it didn't get any water in any of that unless I'm missing something.

ECM and ECU are pretty much the same things Electronic Control Module, Electronic Control Unit. Some manufacturers call them ECU some call ECM and some call PCM. It depends on the vehicle but they all essentially do the same thing.

On another note I've only lost the Speedometer once during a long trip I drove one hour going on a two-hour trip and after one hour of driving, I lost the speedometer which also turned off my cruise control. Thankfully I didn't have to slow down because I was on the highway until the last 6 miles before my house. At which point I had to drive in 1st gear at 3-4k rpm till I got home. Cars flying past me like I'm an ******* as if I could help driving so slow. I was able to get it home but after returning to the house. I turned it off and tried to start and it wouldn't do anything. The next morning it started right up with no issues again. It's been on and off and it does kind of seem like something is still wet and shorting out and its slowly drying out and working. I dunno its all confusing and frustrating.

 

I'm still having issues after weeks of trying to work this out. I'll explain all the things I've tried so far.

It's still not starting sometimes. When you turn the key nothing happens. Sometimes when driving I lose the speedometer and all info on the LCD in the cluster things like the mpg shows - - - on everything like it lost communication with the ECU somehow. It starts acting up mostly when it's really hot outside.

I have pulled out the pilot bushing and checked it and the plug had a little film of oil on it so I ordered a new one. The new one somehow fit into the transmission fine but it wouldn't accept the plug. I couldn't get the plug to go all the way into the pilot bushing so I ended up just pulling the o rings off the new one and placing them on the old one and reinstalling the old one back. I also pulled the carpet on the passenger side floorboard and pulled back the metal plate and checked the TCU and there isn't any type of oil or water damage on the unit. It looks practically brand new.







Here is how the pilot bushing looked when I pulled it out.



I've run many different full scans on the car with an Autel MD808 Elite scanner and it never gives any type of transmission codes. The only codes that ever show up are under the motor as stored codes. Normally a p0400 which is more than likely the EGR valve and then these two have showed up recently.





Sometimes the car does great. It starts up and drives fine. The transmission shifts perfect everything works great. Then just out of the blue, it will enter limp mode or whatever its called get stuck in one gear and then I lose the speedometer also. This happened recently about a week ago the car started up fine for 4 days straight I drove it every single day multiple times to town and even took it on a 2 hour trip from here drove it around there and then drove it back in the same day no issues then on the 5th day I drove it to a little fishing spot I like to fish at and fished for about two hours went to get into the car and it was stuck in first gear when I took off so I pulled into a little pub and turned it off and it wouldn't start again. So I let it sit overnight in the parking lot thanks to the owners allowing me to leave it. I went back the next morning and nothing still wouldn't start! Someone mentioned days before that the module inside the shifter can go out causing these types of issues so I tried something crazy I unbolted the shifter and moved it all the way forward and all the way back several times and it started up. I was able to drive it to the house and it shifted fine and all that. I then drove it for two days and then today I drove it all morning and went to get into it just earlier and it started up just fine. I took off got maybe a mile down the road and I looked down and I had no speedometer it already got stuck in 2nd or 3rd gear and no speedometer so I turned around came back home parked it and turned it off and here we are again it won't start.

So because of this somehow magically making the car start I thought for sure it was the shifter so I bought a used one from a salvage yard in town for $100 and replaced it which did nothing at all it still wouldn't start.

I also thought it was the shifter module because it never registers a gear when it won't start. When you turn on the key S is highlighted but no gear is highlighted and I know as long as it doesn't detect that it's in Park it will not start!




There was also one time I drove it two hours away. I also drove it around while I was down there than on the way back I got only 30 minutes away from the house and I lost the speedometer again and this time it got stuck in 5th or 4th. It bogged out really bad taking off from a dead stop but I was able to get up to highway speeds no issues after a little time and get it back home. I had to drive it like this an hour and a half which sucked not having a clue how fast I was going.

I'm stuck I don't know what else to try. It's bazaar how it's acting I've never had a car do this to me before. I think once I finally work out this problem I'll be putting this car up for sale. Over a month trying to figure out this problem and this car keeps leaving me stranded places. I already know the amount of money the dealership is going to charge me to do anything in this car and I'm not willing to spend that kind of money on a throwaway car. I got this car for only $1000. It needed all sorts of things and I've done a lot to it since I've gotten it but this one major problem is pissing me off. This is my everyday driver so having to keep borrowing vehicles to get to work is getting old really fast. I hope someone can help me diagnose this. I'm super aggravated I spent nearly $200 or so on an awesome scanner and it has been useless in helping me fix this problem.

 

Did you ever come up with a solution for this? My 2004 C320 4-matic is doing the same things you described.