Late W124 cruise control
 

Well, I just discovered another change that makes the facelifted W124s different from the early cars....

The cruise control is completely different.

More to the point....

Last Christmas I installed a pair of tires on my 94 E320 cabriolet. I've got early CLK rims on the car and had one new tire that was a 205/65-16 vice the standard CLK size of 205/55-16. Being frugal, I bought a matching tire from Tire Rack and mounted the pair on the rear of the cab. The fronts remained at the original size, 205/55-16.

Anyway, just before New Years, I had some major health issues, so the car didn't get driven much, if at all for a few months. When I finally drove it far enough to want to use cruise, the cruise failed to engage. It would start to catch, then drop out.

I figured that the control box had failed, so I started to pull the box, only to find that what I thought was the CC box under the left side of the dash was in reality an amissions control box.

This particular car, and my wife's 95 E320 wagon have the traction control package, and my 94 E320 parts car does not.

Turns out the CC control is integrated into the engine idle control on the late W124s, and the traction control equipped cars have a different control box than the non traction control cars. And these units are not cheap in the used market.

Swapping the control units from wagon to cab did not get the CC to work.
Didn't try to do it vice versa, but in retrospect I should have...

What I eventually found out was the newer cars take a signal from the ABS sensors to figure speed. So far so good.

But wait! There's more!

MB decided to not only use the rear sensor for speed input, but they also take a reference signal from the left front wheel, and if the difference is greater than .5%, the cruise does not engage.

Put the old set of tires on the rear axle (same size as the fronts) and the cruise works great now.

Who would have guessed?

Jim

Yes and Amen. Thats a great explanation of the new cruise. The Electronic throttle can be expensive to replace when it goes. All those parts are interconnected and diagnosis can get to be confusing when things go south.

These later model mercs are certainly still DIY cars, but you have to use a multimeter and the FSM alot more :)