Need Help with Codes on W140
 

I have a 93' 500SEL with 140K miles. After leaving the highway last week, the car only had half power. It crawls from a stop and later gets up to speed and runs smoothly. I have no ASR or CEL light on. ( I have been through all that on another S500 I had) I noticed a new tranny fluid leak, so I took it in to get that fixed and have codes read. The tranny protection switch was leaking along with a cooler hose. The codes read were:

17-Crank Position Switch
48-Reference potentiometer
64-Cruise switch
80-Brake light switch

The mechanic thought the tranny went into limp home with the protection switch being bad. He cleared all codes, but 17 will not clear. On start up it runs the same, BAD! Very low RPMS at idle, but no misfire that I can hear. It feels like limp home, but it happens at start up with no ASR light. I know what all those codes mean, except the 48-Reference Pot. I know cruise switch and brake light switch are associated with ASR, but I have no light. Crank position is usually assoc. with hard starting, and I don't have that. What is the 48? The mech. suggests a tune up since I don't know when it was done last. I will do that myself this week end. Mech. said it sounded like it was running on half its cylinders, but I couldn't hear that. He is a very good German car indy. Any suggestions?

Thanks

These beasts (and as you know from having an S500 they are beasts) can have one thing go wrong that creates a domino effect. A tune up may help, but I don't think that it's going to solve your problem. Have you had a Benz go into "Limp home" mode before? It's not a "I think" it's definite. The pedal goes to the floor with no acceleration (your symptom) and the tranny will either stay in 2nd gear or jerks around trying to do something that the computer won't let it do. My mechanic told me that when a sensor goes bad the computer gets a strange signal and gets confused and tries to fix the problem. I might also suggest that if you are getting strange signals from the computer that you might have a bad wiring harness. It is renowned on these early W140s and can cause all kinds of strange electrical problems that don't make any sense. Good luck

Yea, my 94' S500 would go into Limp mode, due to the brake light switch. A very common problem. What baffles me is, I get no ASR or CEL light at all. Can the car go into limp mode without the ASR problem, or light coming on? If so, does anyone know what causes that? I know the ASR light would come on for alot of reasons. I just don't have the light. Could it be the crank position switch with the code that can't clear?

Thanks

Doesn't sound to me like the limp home mode - not if it eventually gets up to speed and runs smoothly. Keep checking the codes and see what comes back first.