2013 Freightliner Cascadia ABS retarder relay shorted SID13 FMI 6

In need of help to figure out where to begin to look to fix this issue any help greatly appreciated.

Light came on with Retarder delay Control Relay current above normal or grounded circuit. And something about the voltage of the diagonal 1
sin 13 FMI 6

Engine is a Detroit dd15
This truck is a 6x2 with 6 sensors and 6 valves it has 2 abs ecm and it has the automatic air lever valve.

1 st ecm is the E versión and the second one is the 6x2 I’m assuming this truck being 6x2 it has ABS, ATC and stability control.

What I’ve tried so far:
I tested all the valves and sensor from the ecu harness and all of them came ok
When testing the sensors with the truck rolling, the sensor front Left does not read any speed.
Diagonal 1 voltage is erratic.
Replace FL sensor light still on.

My hypothesis is that the output signal wire pin 14 on x1 harness is shorted some where. But since there is no actual relay because is control by the j1939 I don’t know where to begin.

Truck has been in multiple shops and no one knows how to fix it.


Note: manual to check continuity to ground between 3rd brake pin (14) on x1 but what I don’t know if it supposed to be grounded or not.