1997 Volvo w/Volvo Engine, compression brake is always on and in the low position

I used to have a 98 volvo 610 with volvo engine with the similar problem, except my exhuast brake is on 100% of the time, even when I tried to accelarate. Could not even pass 40 mph when bobtailing.

My temporary workaround was to disconnect the 1/4 inch black air hose that goes from the EPG controller, which is located at the top of the intake manifold, to the exhaust pressure governor, which is located after the turbo exhuast outlet.

Cut the 1/4 black air hose and plug the opening at the controller side. The controller will supply air pressure to the EPG via that 1/4 inch air hose when it try to close the EPG valve. If you are able to disable the exhuast brake this way then you know the exhuast pressure governor itself is not stuck.

 

You say air solenoid valve, that actuates EPG was leaking.... Yep, it happens. Volvo is truck of unique design! when you apply park brake, ECM applies EPG to warm truck up faster (Swedishhhh feature!) and that's why solenoid valve fails!!! it is not all, park brake wiring may be bad ore air pressure switch may be bad and ECM "thiks" park brake is applied! Driving with EPG closed ruins exaust manyfold gaskets!

Volvos with D12A and D12B are old and it is common problem of these rigs! a half of ex-TransPele Volvo FH12 COE trucks with D12A are with disabled EPGs.