What are these valves

Truck is a Volvo VNL 630 VED12 engine. This valve is located on a cross member just a the rear of the fifth wheel. It appears to be a big square valve in the center of the group, and a smaller valve on each side of it. The small one shown in the bottom of the picture leaks when brakes are applied. What are they called. The electrical plug next to it is not plugged to anything, and has a cap on it. I know Volvo will want an arm and a leg for them. I hoping I can replace what leaks for just an arm.

 

Are you saying that the small one is ABS, or the whole unit?

 

I just left the Volvo dealer. He showed me one with a place to plug that wire that is unplugged in the pic. I didn't get it because the one on the truck is not plugged to anything.

 

Man! I really thank you alot. I take it off tomorrow to get part numbers. The one he showed me was 231$. There has to be a better game in town

 

I am much obliged to you.

 

Thanks for the tip. When I first heard the leak, i thought it was the chamber. Air leaks sometimes seem to move around. I'll check that out. Thanks again.