There have been quite a number of questions about OVP-related problems. I have finally fixed my OVP problems and wanted to share my experience with the forum.
Car: 1986 300E, 171,000 mi. Runs very well.
Symptoms: "Antilock Brakes" warning light came on, somtimes flickering, sometimes on steady, engine stumbled a bit at idle when ABS light was on, the ABS brakes activated even on dry pavement when ABS light was on. Driving over rough pavement seemed to make the problem worse as did long, hot drives. The ABS warning light was slow to go out when starting the car.
My first attempt at repair, using information from this forum was to replace the 22 year old OVP relay thinking it was about due anyway.
Results: the problem went away for about 2 weeks then returned, worse than ever.
My second attempt was to clean the ABS sensors. These needed it. There were metal filings on the sensor tips which I brushed off. I used a dremel tool with a cone shaped fiber brush to reach inside the front hubs to clean the toothed wheel, worked like a charm. While cleaning the sensors, I found that the insulation on the left front sensor was cracked and falling off. A new sensor cost around $150. I went to a pick-and-pull salvage yard and got a set of three sensors from an '88 300E, in like new condition for $5! How's that for a score?
Results: The ABS engagement on dry pavement seemed to be fixed but the warning light still flickered and the idle was still wonky when the light flickered.
My third attempt was to look very closely at the connector where the OVP relay was plugged in. Remembering a forum discussion about a "hold-down: screw on the OVP relay, I realized that my model did
not have a hold-down and the OVP relay was free to vibrate and shake with the car's motion. The relay is a bit top heavy and the shaking had loosened the connectors so that the relay connections worked loose giving the flickering ABS light.
I removed the battery and set the computer aside, unbolted the assembly holding the OVP, fuel, and Klima relays so that I could reach the bottom of the OVP relay connectors. Using a small ice pick, I pushed the connector for each wire on the OVP relay tightly on the relay pins. Then, using a Zip-tie, I secured the relay firmly to the assembly so that the relay could not shake loose. Then I put it all back together.
Result: The antilock brake warning light no longer flickers, the ABS system does not come on when it shouldn't, the idle is as it should be at all times, and the ABS warning light goes out the instant the engine starts.
After two months all is still well so I believe that the problem is fixed!!!
Here was a case where two faults, a bad ABS sensor and a loose OVP connection gave similar symptoms in a confusing manner.
Hopefully my experience will help others. I could not have fixed this problem without learning so much from this forum. Thank you all.
