diff lock switch deactivates tc
ecu wouldnt know center diff lock is locked, there are numerous combinations of wheels spinning some of those been the same as diff locked when it isnt ie 2 wheels on the same side,You tell me what's the difference between these two scenarios, then i'll tell you from wabco point of view
1. unlocked central diff, FL wheel turns faster than FR and RR faster than RL
2. locked central diff in the same situation
there can be a variety of all kind of such scenarios and in each situation the ABS system will behave accordingly... the gist is that the ABS system when it comes to TC has a delay compared to mechanical actions
As i said it's more complicated than it appears, and the main issue is exactly the fact that the ECU doesnt ''know'' the CD is locked and will act like it isnt using brakes to equalise the axle speeds based only on wheel speed inputs while the axle speeds are already similar due to the locked CD
I'm not trying to argue just to discuss about that cos that's what i'm saying too... that the ECU will act like when the central diff is not locked even though it is and the algorithm is based on the presumption that the propshafts are spinning with different speeds so based on all 4 sensor's inputs it will apply brakes all around as to make the propshaft's speeds similar as well without being necessary, but the axles are forced by the locked diff to turn at the same speed already and this will enter in conflict with the applied brakes and as the axle's speed will not be reduced with the expected rate the ECU will increase the fluid pressure in the calipers through the modulator, it's almost like when the driver applies brakes and throttle at the same time on a straight road... i've made such tests with my own car and once in a mud trap where i've passed without problems with open diff and locked diff(with inhibited TC) when i attacked it with cut diff-lock input to ECU i lost all motion in the middle of the mud with TC light on... important is to take into account that the TC has a certain delay cos it has to calculate while the mechanically locked diff is already acting
im not trying to argue either just understand, ecu must have the ability to deal with 2 wheels spinning on the same side with equal axle speed,
tc was inhibited for roller testing with prop off which is obvious as a reason,admittedly there are other scenarios apart from 2 wheels spinning on the same side both axles equal speed ,but since that scenario exists and can be expected to,ecu must deal with it and so not need to deal with more complicated scenarios,brake over heat will occur if tc is used for prolonged times or prolonge down hill,though rare given speeds its needed at,and more unlikely with locked center diff
