The car is a 1988 420SEL with 53k miles. The ABS warning light comes on after each startup, usually within 2 or 3 minutes of driving around, and often after hitting a bump. The light does not go off until the car is shut off and re-started. The ABS does not function.

I had my regular mechanic try and find the problem, however he does not have the computer and code reading software for the 126 chassis. He did, however, hook my car up to his computer as if it was a 140 chassis (which it isn't) and the error code indicated that the control unit had a bad valve?, and thus, the entire control unit would need to be replaced. New this part is $1000, used $200. I'm referring to the unit on the driver's side of the engine bay with "ABS" enscribed on its black plastic cover.

I can either take the car to a MB dealer and have them diagnose the problem (which will be at least $100), or I can just try putting the used ABS control unit in. My mechanic said he has never seen this part go bad before, however there's always a first...

Any suggestions? Does anyone feel confident that error codes for the 126 would apply to the 140 as well, or vice-versa?

Thanks in advance.

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2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey

SOLD:
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino