I have this problem, and from all I read, once air has gotten into the ABS
unit normal bleeding procedure may not work. The dealer has the scan
tool needed to purge the unit during bleeding. Also a good idea to replace
brake fluid at recommended intervals.
it could be abs break unit
ABS systems, in general, have to be bled with a power unit. This forces brake fluid under hydraulic pressure through the brake system and eliminates any air in the system. ABS units cannot be bled satisfactorily without it. Any auto repair shop that does brakes will have the capability to do this.
Follow the 2 brake lines that lead out of the master cylinder, they run to the ABS unit.
On one side (the front) is a vapor cannister and on the rear there is a power brake abs unit and a rear suspension air pump.
The ABS relay is under the dash mounted on top of the abs control unit. There are two other relays for the ABS system mounted in the engine compartment, toward the front driver's side, below the MAF sensor and air cleaner container. They are under a black plastic cover that's mounted next to the ABS pump.
Faulty ABS unit .
The ABS pump relay is intergrated into the EHCU (elecro-hydraulic control Unit) and it is not serviceable. If the ABS pump relay is defective, the entire control unit must be replaced.
Either one of the four ABS sensors went bad, or most likely your ABS computer failed and needs to be rebuilt.
Fix the problem and the light will go out. Normally on Volvo 850's the ABS sensor goes out (actually a wire comes loose inside the unit) this sensor is under the hood on the ABS unit.
lokk in your fuse ox and disconect re abs fuse or find the abs unit and disconnect the wire assembly. Just a word of advise and that is if you disable an ABS or Air Bag system and you are involved in an accident, the insurance company may NOT pay for yhe damages. They are there to prevent injury. CALL YOUR INSURANCE COMPANY BEFORE YOU DO DISCONNECT ANYTHING.
Mikey's abs are real but they were air brushed and outlined :)
There could be something wrong with the ABS system and check the ABS sensors on all wheels. Also check the connections to the ABS unit and the traction control button.