2011 Mack CXU ABS codes MID 77 FMI 7

Hey guys. I have two ABS / TCS that I can't seem to figure out where to look. My understanding is that the codes stand for Brake Load Demand (or command) but I don't know where the sensor is located.

These are me two codes:

1. ABS (136) SID 78 FMI 2
2. ABS (136) SID 77 FMI 7

Both of these codes are slightly de-rating my trucks HP / Boost.

Anyone know if these are air pressure sensors located at the brake pedal (4 sensors inside the cab around the treddle valve / two located under the hood under on the treddle valve. Or are these the sensors that attach to the rear suspension air bags ( two- one on front axle and one on the rear axle)

Thanks for the advice.

 

It's been an on going problem even in dry weather. Are these codes relative to front ABS WSS?

 

Just found this:

Sid 78 Fmi 2: Brake Demand / Load Sensor DTCs / Shorted Brake Demand Sensor (secondary CKT) OPEN

Sid 77 fmi 7: Brake Demand/ Load sensor DTCs / PS not Calibrated


So is it the air pressure sensor by the Brake valve inside the cab that says secondary air? Or one that's on the outside of the firewall? Both says secondary system so not sure with one to look at??