Fix for a constantly running ABS pump motor
The ABS computer module used in alot of older GM and Chevrolet trucks commonly fails in one of two different ways. It throws trouble codes, or the ABS pump motor runs constantly and you have to take the fuse out.
The first problem is caused by cracked / bad solder joints. I think one of the reasons that this happens is because they used such a thin circuit board. Anyway there is a lot of information online about it. Basically you need to take the top cover off and reflow all the major thru hole connections.
The second problem is usually caused by a blown power transistor and/or relay. The motor circuit is stuck on and cannot shut off. This repair takes more time and skill, but is still totally doable at home. You will have to remove the circuit board so that you can access the top side of it. A fair amount of desoldering is required. You will need small torx screwdrivers, a good electronics soldering iron, desoldering wick, a voltmeter, etc..
To get the circuit board off, you have to desolder all the thru hole connectors and the solenoids. 31 different joints on the board I have. Yours might be different. Don’t use so much heat that you damage the board and be careful with your iron. This thing is pretty fragile for an automotive part IMHO. I accidentally lifted a trace on mine which I had to repair.
(..There are different revisions and different models so your circuit board may not look exactly like mine..)
Once you get the board off you can flip it over and look for the failed component. Test the relay and the motor transistor (N Channel MOSFET power transistor).
(How to test a relay in-place:
How to test a MOSFET in-place: )
My relay was good, but my transistor had failed. Replace the bad component, solder it all back together, and done.
Suitable replacement components at Digikey: 2 different power MOSFETs that are higher spec then the original, the relay driver transistor, and the relay