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Stan, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3526
Experience:  Technical support engineer
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I own a mercedes viano 2005 (marco polo), currently I have start issues with the car,

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Hi, I own a mercedes viano 2005 (marco polo), currently I have start issues with the car, when I turn the key, and wait for the dash warning lights to turn off, the ASR/BAS light stays on, and the car won't start (both keys tried).
The problems seems to be related to cold weather (appx. below 8 degrees), all summer the problem was gone, and when I heat the car in the winter I'm able to start the car.
The authorized mechanics have replaced 3 relays without any luck, and they claim that the electrical system is tested without any errors. In their defence, they were not able to reproduce the behavior, I guess they work in a heated garage. Still it's very expensive to let them fool around with the car. So hopefully you could help with some insights in what might be wrong?
Can you please tell the VIN of your van?
Is the starter cranking the engine when problem occurs?
Customer: replied 2 years ago.
I'm not near the car before later on today, so I can't give you the VIN, right now I guess.The car does not crank when the ASR/BAS light stays on. When the ASR/BAS is goes off as it should, then the car starts perfectly and i can drive the car as if nothing is wrong. And as said, the car runs fine in in the summer, no issues.
The VIN is also present in registration papers. It would really help to know it.
Just get back to me whenever it is convenient for you.
Customer: replied 2 years ago.
Hi Stan
This might be the VIN WDF63981313130558, it's just that it's called something different in DK.Br Casper
Yes, that is the VIN.
This type of vans had a problem with main positive connection to the fuses in the engine compartment electronics box.
When the lid is removed, there will be a fuse rail in front of main fuse and relay module. This fuse rail is mounted with torx screws. They must be removed and fuse rail turned. on the bottom side of the rail, there are 2 nuts holding the copper positive connections. These nuts should be retightened. These fuses can have a poor contact, which can be affected by colder weather.
Best Regards,
Customer: replied 2 years ago.
Hi Stan,
I hope I'll have the time to try it out tonight, thanks so far.Br Casper
Hi Casper,will be glad to assist you further whenever most convenient for you
Customer: replied 2 years ago.
I tried it with No success, the asr/bas light is still on, but i do hear a small continous whisteling sound, after all other warning lights turn off, Sounds like it is coming from the electrical box, might not Mean anything, but just to let you know.
Hello Casper,
Both ASR and starter will not work when there is a voltage supply problem from the common main relay module. It is right behind the fuse rail we talked about earlier. I sugggest to wiggle or even heat it with the hair drier when the problem is present. It's part number is ***** and costs about 120 gbp.
The proper way to diagnose this now is to check what is happening with engine and ASR electronics when problem is present. Based on the findings, respective voltage supplies will have to be checked.
But this main relay is a common part, which infuences engine start and ASR.
There is a fan module for cooling the electronic box, which can be running on if there is interrupted communication between electronic units.
Best Regards,
Customer: replied 2 years ago.
Hi, StanSo far no success with wiggling the components, I still have to try to heat on it, to make a final conlusion, but it will not happen until the weekend, I'll let you know about the findings.Br Casper
Hi Casper,
Let me know how i can help you more.
Customer: replied 2 years ago.
Hi StanIt has been a bit to warm for a period, meaning the car had no issues, but the 24 th and 26 th it was cold enough, and I managed to heat on the components in the electronics box, after around 2 minutes of heating, the car was able to start.And also the procedure of starting the car without heading the electronics box, is to start the oil heater, apx. 10-15 minutes, turn on the fans in the cabin with full heat and re-circulation for 5 minutes. And then the car starts as well.So from hearing that what would you propose? And if it means that I have to change the A6395450401 unit, is that a complicated procedure?Br Casper
Customer: replied 2 years ago.
Btw, I thought it was only the BAS/ASR that wasn't turned off, but it was actually more lamps, see attached images.DSC_0017.JPG => Car starts
DSC_0018.JPG => Car does not start.
Hello Casper,
Sorry for the delayed reply,
The replacement of A6395450401 relay box should cure the issue.
All of these lights staying on are related.
It is not complicated to replace the fuse box with some electrical common sense and basic tools (torx bits, small ratchet and wrenches)- battery ground should be disconnected for safety, and location of all plugs should be remembered.
The SAM module will have to be unscrewed and re-installed on the new fusebox.
Stan and other Mercedes Specialists are ready to help you
Customer: replied 2 years ago.
Thanks, I'll try to get the unit changed, I might be able to get it from Mercedes in Denmark. If not, do you know a place, online or other where i can order this unit?