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Literally just got a 2008 C300 on Tuesday, tagged it on Wednesday but wouldn’t crank when leaving the court house. After a bit of toolless troubleshooting I got it towed home. Read as much as I could on possible causes. Steering lock seems to be working and all dash light/headlights are coming on with key in position 2.
Bench checked the relay and it’s good. Getting no negative signal to the relay. So either ECM or SAM right? Not so fast… while troubleshooting, I jumped pins 30 and 87 (not 87A {not sure that matters}) on the relay plug (relay removed) and the car started no problem. BUT shifting to drive and reverse did nothing as if it was in neutral, just rolled a bit because I’m on a slight incline. Is this normal for bypassing the starter relay? Or is this an indication that it might be the TCM or some other shift/transmission issue as in it doesn’t know it’s in park/neutral? I bought it from my neighbor for my GF, it was his daily driver so no known previous issues.
As an afterthought, there is a wadded piece of paper unlocking the shifter. With it in, it will shift with the engine off and on but with it out, it won’t shift at all, not even when I bypassed the starter relay. Not sure if that’s another indication of something specific or if it’s just something else to fix once this no crank issue is fixed…
Do you have a dedicated MB scanner? If you jump the starter the car will crank and even run with EIS in run position. But on W204 the TCM will not allow drive away unless the ECU tells it all criteria of the DAS are satisfied. This may be something in the DAS failing EIS, ESL, TCM. Or maybe the SAM. You need a scanner, not just a code reader, to sort that out.
Ask the neighbor about the “wadded paper.”
Last edited by Odd Piggy; Feb 6, 2026 at 01:51 AM.
Literally just got a 2008 C300 on Tuesday, tagged it on Wednesday but wouldn’t crank when leaving the court house. After a bit of toolless troubleshooting I got it towed home. Read as much as I could on possible causes. Steering lock seems to be working and all dash light/headlights are coming on with key in position 2.
Bench checked the relay and it’s good. Getting no negative signal to the relay. So either ECM or SAM right? Not so fast… while troubleshooting, I jumped pins 30 and 87 (not 87A {not sure that matters}) on the relay plug (relay removed) and the car started no problem. BUT shifting to drive and reverse did nothing as if it was in neutral, just rolled a bit because I’m on a slight incline. Is this normal for bypassing the starter relay? Or is this an indication that it might be the TCM or some other shift/transmission issue as in it doesn’t know it’s in park/neutral? I bought it from my neighbor for my GF, it was his daily driver so no known previous issues.
As an afterthought, there is a wadded piece of paper unlocking the shifter. With it in, it will shift with the engine off and on but with it out, it won’t shift at all, not even when I bypassed the starter relay. Not sure if that’s another indication of something specific or if it’s just something else to fix once this no crank issue is fixed…
The wadded paper indicates that there is an issue with the mechanical gear shift interlock cable with the paper as a "bodge" to override it. This mechanical cable runs from the ignition switch (EIS) to the gear shift linkage. This might indicate that someone has been tinkering with the EIS.
Raise your steering wheel, unclip the gaiter and feel if the cable is connected to the EIS. You might need to remove the EIS to do this, and if so follow the link below and scroll to Sept 18 for pictures and instructions that include EIS removal.
Raise your steering wheel, unclip the gaiter and feel if the cable is connected to the EIS. You might need to remove the EIS to do this, and if so follow the link below and scroll to Sept 18 for pictures and instructions that include EIS removal.
You need a scanner, not just a code reader, to sort that out.
Ask the neighbor about the “wadded paper.”
Depending on the issue, I may not be keeping this car so I’d rather not buy a dedicated MB tool. However, I don’t have a problem buying a universal tool. Would this tool work?
I think your scanner is fine. Drive train CANBUS OFF fault can result in a no start and maybe even a no crank situation. The paper wad in the shifter indicates a mechanical issue in the shifter that may affect the selector and the CANBUS OFF could point to corroded CANBUS connector. Ask the neighbor if the car ever had an A/C drain clog that got the front carpets wet. That’s a common place for this to occur. The connectors under the driver side door frame plate are also prone to moisture and corrosion. This can be a difficult issue to chase to ground, but ultimately solvable.
Drive train CANBUS OFF fault can result in a no start and maybe even a no crank situation.
Where are ALL the CANBUS connections at? I’ll start with the obvious but might need to check them all. Are there connections under both sides of the carpet or just one? How far down under the carpet are they?
Also, I pulled the front SAM and it had very little water contamination on the board (maybe 2 small spots), cleaned it will 99% isopropyl but couldn’t access the other side of the board to check/clean it. I assume it would need to be unsoldered to remove.
We don’t have any more W204s so this is what I remember.
There are CANBUS connectors in the footwell of the passenger seat and I think I remember one under the passenger seat itself. There are also CANBUS connectors under the chrome driver’s door frame Mercedes name plate. Many people have had moisture problems there. Don’t forget to investigate the reason for the wad of paper in the shift mechanism, too. Continue to search around the W204 forum because some people have gone through submerged cars’ CANBUS connectors.
There are CANBUS connectors in the footwell of the passenger seat and I think I remember one under the passenger seat itself. There are also CANBUS connectors under the chrome driver’s door frame Mercedes name plate.
Hopefully the issue is in one of those spots. Thank you. I’ll update what I find.
I dont have a solid answer but maybe a bit to contribute. If the coding in the car gets off in one of the modules it can cause the "has a malfunction" errors in other modules.
Its something to pay attention too. A couple examples I've seen. One was a dash cluster that I changed the wrong setting on and I cant remember the setting off hand. However with this setting wrong it gave me the has a malfunction error for my transmission and central gateway modules. Ans second is the central gateway as it communicates with so many modules it can cause severe has a malfunction errors.
So try to think if anything was replaced or changed that could trigger errors. I've even seen a aftermarket brake booster pressure sensor clear the CEL but cause can buss errors that could be seen in Xentry. Simply replacing this sensor with a genuine MB one fixed all those issues.
So... I found the CANBUS on the drivers side and cleaned it. No change...
I found one of the CANBUSs on the passenger side. Cleaned it and it started. Took it for a quick drive and the transmission was shifting HARD. I brought it back home, turned it off and tried to start it again. Nothing...
Wanted to really clean that CANBUS again, but didn't know if the wires were specific to that port so I labeled them. Took all the wires out at once, removed that plastic bottom part, scrubbed the h3ll out of the bottom with a brush and alcohol again, used a precision flathead screw driver to scrape the pins, then used the largest tip cleaner that would fit in the 2wire plugs and scraped the inside as well. Put the wires back on in order, stuck it in a small zip bag with silica, zipped it to the wires and then used electrical tape to seal the wires and bag the best I can. Put it back in the car with the bag opening on the bottom and then ran the car around town for some weekend errands, starting and stopping multiple times and shifting smoothly. All seems to be good now (as far as it starting). Thank you everyone for your help. I will be starting new threads for the other issues if I can't figure them out on my own. See you guys there...
Glad to see it went more smoothly that I expected. I’ve seen people on here fighting canbus issues for 6 months. Hope it holds! W204 is one of the best chassis in the series. Hated to get rid of mine, but it really didn’t work well going to construction sites 300-500 feet off the pavement.
Hated to get rid of mine, but it really didn’t work well going to construction sites 300-500 feet off the pavement.
It’s the woman’s car so if it hits a construction site, she got her left and right mixed up again while using GPS. It will likely spend 90% of its time at home, going to her mother’s and to Tim Hortons.
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