Hello sounds like you have a couple of problems first of all you said ETS lamp comes on? If thats the case C1120 code is for yaw rate fault stored in the Esp control unit. You said they replaced wheel speed sensors?
The ETS reads wheel speed sensors and stop lamp switch to regulate brake pressure to correct wheel spin on accel. Does the lamp flash,stay on all the time or go on then off ? There is a sequence for different faults.
Also some early MLs had issues with wiring loom at traction control unit at left front frame rail getting chaffed on mounting bracket causing some odd faults.
One more thing the main ground for the traction control unit is W9 and is located behind left headlamp theres a stud welded to body.Sometimes when techs install new auxillary fan harness kit they cant get nut loose and break the stud and just screw them with a sheet metal screw causing poor ground and setting faults. Tim