I am very grateful to Duke for his accurate advice on the OVP relay. I own a 1992 mercedes 190E (W201) whose ABS light came on during the cold weather just after Christmas. The next time I tried to run the car I had terrible difficulty getting it started and nearly flattened the battery in doing so. When I did manage to start the engine, the ABS light remained on and there was no idle control - and then I knew the car wasn't safe to drive until the fault was fixed.

Following Duke's instructions, I removed the battery and found the OVP relay behind the soft removable pannel. It wasn't easy to spot as it was in a dark area behind the cradle that holds two 'ECU' systems, against the bodywork and towards the engine side of the cradle. I had to carefully cut some of the front black plastic cradle with a hacksaw in-situ in order to lift the two 'ECU' units out, whilst leaving them still connected. The old OVP had a black top with a single fuse; another reason why it was difficult to spot. The part number of the old OVP was 201 540 32 45 and had seven pins. The new OVP has 9 pins and a red top containing two fuses (I presume the red is to make it easily, visible). There were two spare pin holes in the socket which weren't used by the old OVP relay - the pins on the new OVP relay simply used up the spare two holes in the socket. The part number of the new OVP is 201 540 37 45. I bought this for £58 (including VAT) at Mercedes Parts at Brentford.

When I test ran the car, it fired up straight away without any problem at all. The ABS light has remained off all the time and the car has been running perfectly ever since.

I am really pleased to have the car working again. Without this forum I would have needed a specialist, as I have little understanding of the electronics on modern cars. There is no doubt that the accurate diagnosis of the OVP fault has saved me a great deal of trouble and money. Thank you.