I have an ABS light which cannot be switched off, consequently my Volvo 850 Estate has failed it's MOT
How do we switch the light off or do I need a new ABS Module and if so, where do I obtain one

 

You would switch the light off by solving the problem or simply erasing a false code. The first step is a scan with an appropriate scan tool, or the self diagnostic port on the car to determine what the ABS unit thinks is wrong. Then using a reasonable diagnostic process (guess, replace and try again is not reasonable) determine the best course of action to solve the ABS problem. Could be a module, could be a pump, could be a broken wire, could be a rusted off tone ring, could be a bad sensor, could be many other things. Some of those early ABS systems were not easy (at least for me and my shop) to diagnose. What year is your 850 - acouple of different systems were used depending on the year - For 1996 and up cars you can get a replacement module from a company I have used hundreds of times - xemodex. However there may be many other closer to you in GB or the EU.

For a cheap fix on your 850 - why can't you just take the light bulb out in the dash? Is the warning bulb function checked during inspection? I'm not advocating driving with a malfunctioning ABS - the rear brakes can lockup too easily with a broken ABS with possibly very bad results.

 

which year is your 850? 93-95s used the "OBD1" sensor where you can read the fault codes from the breakout box (front right). 96-97s were the first years of the OBD2 system. To get an idea of what can cause the ABS light to set check out volvotips.com

You didn't mention if the brakes behave normally and if the light comes on with the key start or after a bit of driving. Does the speedometer behave normally or has it dropped out and come back on from time to time? Anything else odd going on?

Common causes can be the ABS pump, ABS controller circuit board, the wheel sensors, the wiring/connectors. Things you can check for yourself 1) Check fuses/relays? 2) inspect the inward side of the wheel hubs - any signs of grease say from a torn axle boot? (this can get thrown onto the inside of the hub messing up the wheel speed sensor). 3) inspect wiring/connectors to the ABS controller - check for any loose/damaged wires, cracked connectors etc. 4) read the fault codes. If you have an early model Volvotips.com shows how to read codes from the diagnostics port. 96+ requires an appropriate OBD2 scan tool that can read ABS codes as well as supporting the early ISO prototocol. May be easiest to go to a Volvo friendly repair shop or dealer to get your codes.

If you wish to try and pop out the bulb (and hope the MOT tech doesn't do a bulb check ), look for a Youtube vid for fixing the odometer - they'll show how to push up the dash cover to access the back of the gauge cluster. There's like 7 screws starting by the door, inside the left (or right in UK) air vent, then along the edge of the dashpad over to the glove box. Disconnect the battery (since there's an airbag in the dash), remove the screws, prop up the end of the dash cover (it'll bend the 8-12 inches required) then you can access the cluster. The bulbs all screw into the back so you'd need to locate which one is the ABS vs other lamps.

PS - Not uncommon for volvos to develop cracks in the solder joints in the ABS controller board - good news is you can swap out without any programming.