Cruise control not working

[m47fys]

Hi, this is my first ever post and I had to ask my 19 year old son how to do it.

Anyway, I have a 124 series 280 saloon. The cruise control is not smooth, i.e. it makes the car behave like I am constantly pressing and releasing the accelerator. Eventually the action becomes so extreme that it cancels itself. Does anyone know which component is the most likely cause and if it can be tested, repaired or is it a case of just replacing the faulty part.

 

[Langintes]

Relay defective ?

I have this problem only when driving on 80 km/h +/- 2. I have done nothing else than avoid using the CC at that speed.

In my Owners Workshop Manual: Mercedes W124 1985-1995 from Brooklands Books, there is Caution about that says:

If there is "jerking during cruise control operation over approx. 60 km/h" in vehicles with a cruise control, remove the relay for the cruise control and connect terminals 2 and 3 with a test lead. If the problem no longer occurs during the test drive, replace the relay. Otherwise, test the electrical leads for interference according to the wiring diagram.

I have once lost my cruise control cause of excess load and only thing I did to fix was shut of engine and back on.

Regards
Langintes

 

[Bolide]

Faulty cruise is pretty standard on W124s now. I am told that the system detects speed via the speedo and that a bad speedo cable, causing a wavering needle, causes problems with the cruise. If anyone can confirm this I'd be obliged

Also the amplifiers tend to fail. There are instructions here:

http://www.mindspring.com/~houlihan/merc/cruise.htm

http://www.fix.net/~gdl/testproc.html

IMHO we need an FAQ / repair sticky for cruise so interested parties please chip in

Nick Froome
www.w124.co.uk

 

[television]

I have this problem only when driving on 80 km/h +/- 2. I have done nothing else than avoid using the CC at that speed.

In my Owners Workshop Manual: Mercedes W124 1985-1995 from Brooklands Books, there is Caution about that says:

If there is "jerking during cruise control operation over approx. 60 km/h" in vehicles with a cruise control, remove the relay for the cruise control and connect terminals 2 and 3 with a test lead. If the problem no longer occurs during the test drive, replace the relay. Otherwise, test the electrical leads for interference according to the wiring diagram.

I have once lost my cruise control cause of excess load and only thing I did to fix was shut of engine and back on.

Regards
Langintes

Välkomen till vår forum Langintes

 

[Langintes]

Cruse control, dashboard light, front screen bottom rubber seal

It is a shame that I have not checked my relay yet having that tip. I seldom use my CC here because of few freeways or autobans.

Malcolm, thank you. This is my second registering, I totally forgot my old login and password and have since changed email. I got back because Im now dealing with faulty Heater blower motor and have consumed lot of info about refitting it and etc. I was a lot here 3 y ago about problem with fog on windows during wet weather and no light in dashboard. Both are fixed now. The steam problem was leaking rubberseal under wiper column, water had free way running down to the pollen filter and my heater worked as a humidifier

 

[Langintes]

Speedo cable

Faulty cruise is pretty standard on W124s now. I am told that the system detects speed via the speedo and that a bad speedo cable, causing a wavering needle, causes problems with the cruise. If anyone can confirm this I'd be obliged

Also the amplifiers tend to fail. There are instructions here:

http://www.mindspring.com/~houlihan/merc/cruise.htm

http://www.fix.net/~gdl/testproc.html

IMHO we need an FAQ / repair sticky for cruise so interested parties please chip in

Nick Froome
www.w124.co.uk

Tanks Nick this my be my problem, 80 km/h could be critical speed for my cable to vibrate cause of its inner frequency so to speak.

Jóhannes

 

[m47fys]

Cruise control

Thanks for all the info, web site links etc. I decided to try the easiest option first - making sure the wheels are all the same size. I replaced a well worn rear tyre and this has made a big difference. CC now works well at speeds below 45mph, it gets erratic (scary) above this, to the point where it will not work at motorway speeds.

Interstingly, my speedo is very stable at speeds above 50mph but wobbles about below 50mph, which on face value seems to contradict the suggestion that a faulty speedo will affect the cruise control.

I'll try a new speedo if it is not hard/expensive to change.

Regards
DB

 

[stever]

I understand that the usual culprit is the amplifier, which will exhibit symptoms like you describe, and eventually fail altogether. These people repair them: www.remanufactor.com

I've not used them so can't comment on their quality.

 

[JEZ.S320L]

Thanks for all the info, web site links etc. I decided to try the easiest option first - making sure the wheels are all the same size. I replaced a well worn rear tyre and this has made a big difference. CC now works well at speeds below 45mph, it gets erratic (scary) above this, to the point where it will not work at motorway speeds.

Interstingly, my speedo is very stable at speeds above 50mph but wobbles about below 50mph, which on face value seems to contradict the suggestion that a faulty speedo will affect the cruise control.

I'll try a new speedo if it is not hard/expensive to change.

Regards
DB

It's also worth checking the correct tyre width - as this will impact on the rolling diameter which, in turn, will make the c/c 'brain' think that the tyres are slipping, and disengage the c/c (particularly at higher motorway speeds).