ABS WARNING LIGHT ON VOLVO V70 1997

ABS light comes on with ignition then should go off when you start the car.
If abs sensor does not turn off after disconnecting the battery, then there is a real problem, a faulty sensor or ABS malfunctioning.
When the ABS led comes on immediately after you start the car and stays on usually is one of the relays.
The main one is called surge arrester relay, if it is faulty usually there have been an overvoltage.
There should be two more, usually located behind the black plastic cover of the ABS.
Testing and changing the faulty relay can fix the problem.

If light turns off on startup, and comes back on when you reach some speed, usually you need to check the wheel sensors. You test them unplugging the sensor located behind the wheel and testing it for continuity with a multimeter.
Use Haynes manual to find locations and specs of relays.
Contact a qualified mechanic if you cannot fix it yourself, problems with ABS may compromise safety of the vehicle.

Be very careful of BBA-Reman and other web rebuilders. Yes, they will replace parts inside your computer, but if this does not solve the problem you're simply out the money. They warn you about this on their website and Ebay store. The thing that really sucks about the Volvo system is that you can fail the ABS computer, or the pump, or one(or more) wheel sensors, and the system won't generate any trouble codes. That translates into $$ spent at a repair shop, while they experiment just like you would at home. Listen to Ginko. Test your wheel sensors one by one. Rebuild/replace the module as the last step in the chain. Take it from one who spent lots of money on so-called experts who did little more than check-and-replace until the problem went away.

I had the same problem. Undid the rear ABS connectors, cleaned them, added some WD40 and no problems now for three years. It's a while ago now but I think I had to get access to one of the connectors through the rear under the spare wheel area.

Regds,
Dave

Volvo has lots of issues with this. If you have a speed sensor code for the right rear wheel speed sensor that keeps coming on, then you need a computer. New or quality reman is available.
35 years working on Volvo's professionally.

Its most likely the ABS Control Module. It can be rebuilt at BBA-Reman. Just Google BBA.