95 E320 Speed Control Over 70mph
 

The speed controller works perfectly at any speed below 70mph. But it will not engage above 70mph.

Does anyone have any suggestions on how to troubleshoot this problem? Or has anyone had a similiar problem?

Check for equal tire pressure and same tire sizing....

Arthur

Very interesting comment. This problem arose after I installed different tires on the rear axle then on the front - all the same size, but different.

Do you think that this could be the cause of the problem?

Car have ASR??????????

Does have ASR which is working w/o issues. When the ASR normally activiates, a BIG yellow light comes on in the middle of the instrument cluster. This light does not activiate at all when I attempt to command the cruise control on at speeds over 70 mph.

Does the cruise control logic look at the speeds of all 4 wheels? Or does activating ASR automatically disengage cruise control?

Thanks good discussion!

ASR uses speed sensors for all 4 wheels, so this logic gets monitored for comparison on CC.. so all tires have to have the same rolling circumference.. [ ie.size/and PSI]
Discrepancies are most noticed at higher rpm..

Thanks Arthur - new tires all around are planned for this spring. This is the first MB "problem" that is fixed at NC.

I'll confirm this spring. My co-workers were giving me gas and saying that the MB is so smart, that it did not allow the driver - me - to exceed the posted limit! Thanks again

An easy measure for rolling circumference is to mark each tire at the bottom with a chalk line and a mark on the driveway at the same spot.
This line would be where the the tire's plum center-line meets the pavement...
Now roll the car foward one full tire revolution and mark the pavement again... the distance between the pavement marks should be the same for all 4 tires .. this is the Rolling cicumference of each tire and you can now see were tire pressure can make a difference [ along with different brand tires]

Your difference in circumference is more likely due to the full tread/worn tread difference rather than the tire construction.

The most common de-activate C/C trip w/4 wheel sensor comparison is an under-inflated tire.
Thread wear parameters are usually well within The allowable tolerence difference of the module.

Speed Control Issue Resolved!
 

I finally got a new set of tires installed this week. So now all tires have the same circumference. And just as Arthur Dalton said, the speed control is now working above 70 mph without issue.

Thanks for the help. I have 180kmi on the clock and I'm off towards 250 kmi!

Cool......

I'm a little late, but great call Arthur. Once on the '94 wagon I had Michelin MXV4 Plus' on the front and MXV 3s on the back and even though they were both 195/65/15 the MXV 3s were 2 mm different and shutting down my CC. Took the MB dealer 3 visits to figure that one out.

...as Frank Perdue would say... " ..wadda they kno' 'bout chickens, anyway ??????