code spn3598

hello.i am currently getting these codes on western-star with s60 14l. and my jake brakes are only working on the lowest setting.this happened after i drove on really bumpy road.
SID-155 fmi 4 System Diagnostic Code #5 Engine
SPN-3598 fmi 4 proportional valve bank 2 circuit failed-- low ECU Power Output Supply Voltage #2 Engine
we followed the Detroit service information bulletin(https://ddcsn-ddc.freightliner.com/cps/rde/xbcr/ddcsn/412-13.pdf) for this code and did all the tests.we also replaced the engine harness.still getting the code.my mechanic is recommending replacing the ECM.is there any other tests we can do?wanted to get second thought before spending the money on ECM.thanks

 

anyone??

 

well we replaced the ECM the code was still active.after doing more diagnose it turned to be EGR valve.somehow coolant ended up in the EGR valve shorting it out.(starting to think the EGR cooler is going out) the same wire that applies voltage to EGR valve it also supplies the jakes and the doser valve and few other sensors from the ECM.we didn't catch it first time when followed the Detroit service information bulletin because it didn't mention anything about turn key off/on when unplugging each plug at the harness.it just mentions to unplug and see if code goes inactive.i guess on the Detroit the ECM doesn't reset unless its key is off/on.but truck is back up running after $2k.i guess live and learn.