I have a 1999 S500 that is overheating. The auxilary fans aren't coming on. The check engine light is on. Can anyone provide advice on checking the switches or relays?

1) Check ur fuses
2) Is ur AC freon low?
3) Is ur aux fan/s clogged with dirt that they cannot spin
4) There is an AC relay in the fuse box. Check that.

Report back what u find out.

You really need to check for fault codes. That Check Engine light is trying to tell you something important. As far as the overheating, there are MANY things that can cause that. Coolant age and level, hoses collapsing when hot and at rpm, water pump, clogged radiator, worn out viscous fan clutch (that was my problem), etc.

http://www.v12uberalles.com/pulling_codes.htm

http://www.v12uberalles.com/fan_clutch.htm

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Thank you. I do like the idea of owning a scanner since I also have 3 other MBs, but see the Trisco Palm scanner is no longer available and the recommended source said their scanners start at $2500.00. Is there another scanner you'd recommend? It would be terrific if something was available to plug into a laptop. Are any of the OBDII scanners on Ebay any good for a '99 S500?

Just as an FYI, I'm using a $75 handheld digital code scanner (OBDII) that I bought on eBay. It reads out all generic engine codes on my '98 E-class (W210). It's also been useful on a hot rod project car which has a Ford engine and computer, and I once reset the MIL (check engine light) on a friend's Acura too. So yeah, I think for the price you can get a lot of value out of one of these little gadgets. For a bit more, you can usually find a cable and laptop software solution, but I've never experimented with that myself.

Cheers, John

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'98 E300TD (W210) | Sold 6/09 with 205k and counting
'04 VW Touareg V10TDI

THanks for the feedback. I did compression test and a leak down test and cylinder #7 leaks bubbles back into the coolant reservoir, so it looks like a possible head gasket problem.
I've heard that it is possible to pull and replace one head gasket without pulling the intake manifold on some V8s. Is this possible on the 1999 s500 engine, or should I not take any chances and pull the intake?

Autozone will read the codes for free. All you need is a basic OBD2 scanner that you can pick up for a few bucks at Sears. SDS its not, but they are good enough to figure out most problems.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200