mario 500

Hi guys,

forgive me if this one has been done to death!! I have looked back to see if i could find this thread but no luck..

My cruise control just stopped working!! I seem to remember reading about this problem before but can't remember what the fix should be.. Could it be something simple like a fuse or whatever, or is it more complex? point me in the right direction please, as it is cold out there today (uk).

thanks mario 500

Kestas

Yes, look for a blown fuse. Here is some additional information from my personally archived notes:

"Typically it is the amplifier under the dash that causes the most problems. The servo and the stalk switch can also cause problems. The amplifier tends to have solder joint cracks that cause intermittent operation, the typical first symptom of trouble. Make sure all linkages at the engine are cleaned and lubed with transmission fluid. There are testers that can quickly diagnose CC problems."

mashbury

There are 4 major elements involved in the cruise conrol system: the actuator inside the engine bay that drives the throttle linkage, the speed sensor located in the instrument display, the control switch, and the amplifier/ control module under the driver side dash (RHD).

If it went intermittent before packing up completely, this would point to the amplifier. It seems to be a well known fact that they pack up after around 10 years, as did mine, but they typically can be repaired by resoldering the circuit board joints (as I did).

There are definitely threads around to help you with all this..try searching again. I've spent some time around this system tracking down my fault so may be able to help if you have a more specific question.

Couple of things: I think there is a fuse (fuse 8?), best to check with the label on the inside of the fuse cover. The other thing is to check that your brake lights are working, and the contacts in good order: the cruise control uses the filaments of these bulbs as an earth return.

Good luck (s'not so cold down south!).

mario 500

thanks for all the info guys..

well it isnt a fuse - had a look today!! much to my disappointment!!..
It wasn't an intermitent fault either... I use the car only at weekends to do a 120mile trip (one way), and its been fine since I got the car .. So maybe not the amplifier?? Will check out the linkages and actuator tomorrow if it warms up a bit lol..
Any other sugestions are much appreciated..

regards Mario 500

Kestas

I don't know if the E320 suffers this malady, but the common problem for nonworking cruise control on ML320s is the brake switch.

mario 500

Hi Guys,

Well my cruise has come back to life all of its own accord!!! One thing I seem to remember when it died on me is that the revs in top gear where very high compared with normal - at 80 mph they were 4000rpm !! they are normally 3000rpm at 80 mph... So I guess that the gearbox needs a service? It seems as if it just didn't get into top gear.. Question - Has it got to get into top gear before the cruise will opperate? I personally didn't think so, as I know the cruise will come on at speeds above 40 mph!! Maybe there are two faults there unrelated?? But me thinks there is a connection between the two.. maybe the fault lies with the cruise and it affected the gearing - maybe the other way round?

any suggestions will be greatly appreciated..

many thanks mario500..

superb forum .. got me out of the .... a few times

Kestas

It looks like you're getting to the bottom of this problem. I'm pretty sure most designs require the transmission engaged in top gear for the cruise control to work.

If you're going uphill or otherwise accelerating with the cruise control engaged, the cruise control will kick off if the transmission downshifts.

For starters, check the transmission fluid level.

mashbury

IMHO I don't think the cruise system is linked to the gearbox in any way. For example, if you `resume' 70mph via the cruise control while doing say 30mph, the car will accelerate up to 70mph quite quickly and may well shift down to achieve this. Not surprising really as the cruise acts mechanically on the throttle linkage, so it is just the same as using your foot.

Could be wrong but..

On that basis I would guess that your problems are unrelated.

Anyway if all is working correctly now, you can test out the various ways in which the cruise operates, so you'll know what it should be doing if it goes wrong again.

BTW I think the cruise control will start at any speed above 40kmh (not mph).

mario 500

Mashbury,

I think you are right... Thats why I was puzzled that these two faults came and went exactly the same time .. I don't know enough about cruise or auto boxes to say for sure.. One other fault the box has, is that it makes the car shudder slightly when shifting from drive to reverse and back again - so I know it needs a service... The last guy I spoke to about this said the (belts) or something like that need tightening?? any comments from the techy's greatfully appreciated..


Thanks for your reply Mashbury..


mario500