1989 Mercedes-Benz SL-Class CEL

1989 Mercedes 560 SL. Check engine light on. Mechanic cannot find problem. Safe to drive? 160,000 miles, garage kept, all maintenance performed as advised.

Who knows if it is safe to drive? What did the mechanic say the error code was from? Did he reset it (turn it off)? And if he can’t find the problem, that doesn’t mean there isn’t one, it just means you should find a better mechanic.

There is no way we can answer your question with the info you supplied, Sorry.

Just how are they trying to determine why the check engine light is on

I believe there are 2 methods to determining WHICH code you have . . . blink code and impulse counter

And once you’ve determined if there is a code, you have to check for codes AGAIN, to see if there’s a second code, for example

It’s been a few years since I’ve retrieved codes on Benzes of this era, but I believe I got the major parts correct

If the car is running well, it’s quite possibly something minor, such as an oxygen sensor code

But don’t go replacing it, just because that idea popped into my head

Another thing . . .

The guy who’s working on it, does he even have the code chart? If he doesn’t, go somewhere else. Suppose you’ve got the code . . . a number, as I said earlier . . . but you don’t know what it means? The same number code will mean different things for different manufacturers, on these OBD1 vehicles, such as you have

In all likelihood, you’ll probably have to go the dealer, or find a reputable independent shop that specializes in Benzes

And even so, the guy who does wind up properly diagnosing and repairing it will probably turn out to be a middle aged guy. In other words, a 22 year old whipper snapper is probably not your best bet. No offense intended to any young guys reading this.

And even after you’ve replaced a faulty part . . . assuming the diagnosis was correct . . . there are certain procedures which have to performed afterwards, to prove the problem is resolved. This is known as verifying the repair. This is where patience comes in. Otherwise, you’ll just assume everything is fine, and we know what happens when assumptions are made

Might even have to check and/or adjust the on-off ratio afterwards. And that was just one example