found a service bulletin on this code 40

Issue:
The truck has Error Code 40, M contactor detected closed when commanded to be open. Test AA should be greater than 18 volts for a 36 volt truck, but we get 0.00 volts. Also ran test O3 which says the M contactor is OK.

Cause:
Short to B- (battery negative) or frame by cables or components (Q1, Rec1, Rec2, Motor etc.). The M contactor or the Vehicle Manager may have failed.

Resolution:
There is short to B- or frame. Check for a short to frame. The motor may be the problem. Check all components to B- (Q1, Rec1 and Rec2). If there are no shorts, then the VM (Vehicle Manager) has failed. When you measure 0 volts at M sense line (test AA) that means you have a short somewhere. The sense line is pulled up internal to the VM by a resistor to B+ (battery positive) and must measure 18 volts or more. So again, either there is a short somewhere in the armature circuit or the pull up circuit in the VM has failed.