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Mercedes cruise control problem

mark156mark156 Posts: 1,992
edited March 6 in Mercedes-Benz
I have a 1990 Mercedes 500SL with 45,000 miles. The cruise control has started to act erratic. Once the cruise is set, it will just disengage itself. If I use the cruise control lever to accelerate, it will start to accelerate then just loose power. Sometimes, the cruise won't set at all.

What do you think the problem is? I would like to have an idea what's going on before I take it to the shop.

Thanks in advance, Mark156


  • swschradswschrad Posts: 2,171
    if this is a vacuum-operated cruise module, they are supposed to drop out if they are iffy... and with age and time they get iffy. the control unit probably needs replacement, although it might just be a splayed/leaky vacuum hose.
  • mark156mark156 Posts: 1,992
    Thanks for the info Scott.

    If there is a Mercedes mechanic out there who knows if my cruise control unit is vacuum or not would be appreciated.

  • ecainismecainism Posts: 1
    I had a similar problem when I first purchased my used 1994 SL500. At speed (above 65 mph), the thing would disengage; it would also do it on hills. The non-stock 18 in wheels had low profile tires which were not "matched." The front tires were 245/40 and the rears 285/35. When I changed the tires to 245/40 and 275/35, everything was fine!
  • mbukukanyaumbukukanyau Posts: 200
    Has anyone who has owned a 500SL cross shopped with the new Cadillac XLR?
    The Cadillac is getting good press. I would like a consumer opinion. Thanks
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 45,974
    Wrong board for that question. Try over in Smart Shopper or Coupes & Convertibles. Try not to make multiple posts or "spam" all the boards. Thanks!


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  • mpyles1mpyles1 Posts: 90
    First, apologies to Mr. Shiftright for answering mbukukanyau's question here. I tried the Smart Shopper and Coupes & Convertibles boards that mentioned Mercedes, but they were "read only" boards.

    I just bought an SL500 that, so far, is wonderful. Yesterday I was reading the new Road & Track comparo of luxury convertible test drives that included the SL500 and the Cadillac XLR. One thing jumped off the page at me. The XLR rear window did not line up when raising the roof, and the driver had to hold the window in place to get a tight seal.

    This comment harkened back to my days with a 1998 Corvette, which I traded after 13 shops visits in 15 months: roof leaked because the drop-in panel did not seal, brakes rotors warped, 3 electronic control module failures, front tie rod came loose, etc.

    I just traded in an Audi S6 to get the SL500. The Audi was a great car, save one problem that had it in the shop on average every 12 weeks over 17 months -- the On*Star Telematics module kept failing. And guess who makes the module? GM!

    My advice, for what it's worth . . . stay as far away from GM junk as you can. It will take them at least two model years to work out the kinks in the production run, and the quality levels will still be well below par for the price class.
  • mark156mark156 Posts: 1,992
    The 1990 Mercedes 500SL that I mentioned at the beginning of this forum is working fine now. I didn't change anything but the cruise is working as if nothing ever happened. Accelerates by using the cruise lever and de-accelerates by the same method. Maybe there was just a glitch that day. Who knows? I'm just glad I didn't have to take it to the shop.

  • I have a 1988 Mercedes 300SEL. The cruise control switch failed and I now have the replacement part. I was so proud of myself for going on-line and getting the right part. I expected a switch that I could just slide on a male connector but this came with the switch attached to the level with about 4 feet of wire with a connector on it. Do I have to remove the steering wheel to install this thing and if so how do I disable the air bag so I don't get a little more excitement then I really need? Thanks.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 45,974
    I don't think so. I think you can drop the access cover under the dash and get to everything that way. You may need tiny fingers so be prepared to hire child labor.

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This discussion has been closed.