ABS Issue

I have a 04 Freightliner Columbia with a 465 Mercedes. I've been having problems with the ABS system for a while now, and even the mechanics do not know what could be causing the problem.

Problem:
ABS-136 code on dash.

Have replaced many parts:
1st time at mechanic: replaced abs computer, front r/s abs sensor and rear l/s abs sensor -shorted, r/s front modulator valve, rear abs harness

2nd visit: l/s front modulator valve, l/s abs wheel sensor, abs plug (computer side), front abs harness

now its coming up with codes again:

SID 7 - Left Front Modulator Valve Open
SID 1 - Left Front Wheel Sensor Open
SID 2 - Right Front Wheel Sensor Open
SID 8 - Right Front Modulator Valve Open

Same code on dash.

Light did go out for 6 hrs after they replaced everything the first time it was in shop, but has been on steady since.

Any idea what could be causing this? all the wheel sensors have been replaced. Is it possible to blow the brand new computer in 6 hrs?

Everything I've found online says replace the modulator valves, however they are brand new. only have 200km on them. same with all th other new parts.

any help would be great, as they are saying I must go to the dealer now because they "give up" and cant cvi my truck until its fixed.

 

I did find a document online stating fault codes with meritor wabco abs systems. its pointing to a "x2 connector". something to do with voltage in the pins.

as for steering play, I just had the steering shaft, wheel bearings, and seals replaced. If that is what is causing this, could the codes still show up after the fix as "stored codes". I read that they have to be deleted and only active codes will show after that.

Thanks for the ideas. I'll be sure to pass them on to the mechanic in the morning. I can't afford the $132/hr at Freightliner after being down for 3 weeks.