W203 cruise control not working

[MBJH]

Another issue with the in laws new merc, the speed limiter works but the cruise control doesn't.
He has one error message, BAS, brake assist visit workshop.
I have searched and the main response is brake light switch faulty, replace at £10, bargain but would this stop the cruise control working. We kind of think it would as it may believe the brake is always on, or know of the error and know that pressing the brake would not stop the cruising speed.

Now for this fault would an obd2 code reader pin point the problem or do I need to take it to someone with STAR?

He says it all works fine and has no problem braking or using the handbrake etc.
not sure what info you need but it's a 2001 c270 cdi auto.

Thanks in advance.

 

[Ted]

Check your tyre pressures, also check correct tyre fitment.

 

[miro]

You can't assume the BAS (ABS) is working fine. If the car is an early 2001 built then it is most likely a total failure of the ABS system as this is a known age-related failure in that part number.

The parts of this unit are incredibly expensive because it was only in production for a very short period of time. Therefore demand is high and supplies of used units are very low.

The alternative is to take one of the used ABS units from a much newer W203. These are extremely common and much easier to get. The catch is that they are wired with a different data connector and the yaw sensor / lateral sensor in the rear are also different.

So it just depends if you are lucky to have a W203 with the newer type of unit.

This is a worst case scenario. It might also be something like a broken wire.

 

[MBJH]

Thanks for the quick reply, I shall get him to check those, would it show a separate tyre fault if that was the case though?
Also, lets say it was the brake light switch, if I replaced it would the light go away or would I need to get the message cleared?

 

[MBJH]

Miro - how can I check if its fitted with a later model unit.
It is a 51 plate made in December of 2001.

 

[miro]

Miro - how can I check if its fitted with a later model unit.
It is a 51 plate made in December of 2001.

Send me the VIN and I will look up the part numbers. Do check if the rims are standard and the tyre profile is correct.

 

[MBJH]

I shall try get the VIN to you later today if that's ok?

I think it has 16" 5 spoke merc alloys, but I did wonder if they were standard as I normally see these with 7 spoke alloys.
I will also get him to check the profile, where would it say the standard tyre size etc?
I take it pressure amount is on the fuel cap.

 

[miro]

I shall try get the VIN to you later today if that's ok?

I think it has 16" 5 spoke merc alloys, but I did wonder if they were standard as I normally see these with 7 spoke alloys.
I will also get him to check the profile, where would it say the standard tyre size etc?
I take it pressure amount is on the fuel cap.

Yes, the fuel door. Sometimes dealers get special prices on rubber that is pretty close but not same. It drives the car mental above a certain speed relative to discrepancy.

 

[MBJH]

I can't pm yet as I don't have enough post and don't really want to post the vin publically.

 

[miro]

This type of ABS (BAS) is the early type. The car was built one month before the changeover to the later design.

Hopefully it will be something trivial. If it turns out to be the main module then I can post part numbers accordingly.

 

[MBJH]

Miro - Thanks for your help, if it does end up being a big job/unit that needs replacing I will come back to you for a part number, like you say hopefully its a trivial thing.

 

[MBJH]

Result, in law got the brake light switch fitted and it now works (he did have the code read to make sure it was the correct issue)
But now his cruise control works upto 50mph, 49mph set and it goes along fine click it up to 50 and it turns off.

 

[grumpyoldgit]

I probably can't help, but to assist others (miro), what happens if he tries to engage it at speeds above 50 mph?


Just in case it is a faulty ABS unit, there's a member on here who is breaking a 2001 W203 at the moment. Link... http://www.mbclub.co.uk/forums/classifieds-general-sale/143965-breaking-203-c320-petrol.html

 

[miro]

Result, in law got the brake light switch fitted and it now works (he did have the code read to make sure it was the correct issue)
But now his cruise control works upto 50mph, 49mph set and it goes along fine click it up to 50 and it turns off.

I would check the rubber ... sounds like an illogical tyre has been fitted.