yes the fuse is for the haldex only, but in order for it do it's job properly it relies on a number of sensors (all very well documented) including the abs/ecu unit. So by removing the fuse for the haldex you in fact knocking out all of the additional elements that feed into the haldex and thus assume it must be the haldex controller. After all it could be one of the longtitude/latitude sensors feeding incorrect information when turning on full lock and thus telling the haldex to apply rear left or right wheel brake. Yeh disabling the fuse and problem has gone, but that because one of those sensors is not managing to send it's information to the haldex and not the fault of the haldex unit itself (after all it's simply doing what it's told).
On the other hand I'm just not sure you can actually isolate individual elements before removing the the haldex fuse as you wouldn't know how the haldex will react to lack of certain information it receives - it may just render it inoperative i.e the same as pulling the fuse out in the first place !
And hey, don't forget it may still be the haldex controller all along
Long/lang sensors, steering position and abs sensors operate without caring if the haldex is there or not... ESP is available on FWD cars too...
The Haldex has nothing to do with left/right brakes at all... its a clutch pack... all it does is connect drive from the prop shaft to the rear diff... thats it... its the ABS controller and the that manages ESP...
ABS, ESP and Haldex AWD is a modular system but there is of course dependencies along the line... ABS is essentially top of the tree... when you have an ABS fault you lose ESP and essentially AWD too... this would show up as an ABS fault... ESP is a function of ABS so ESP control is lost when certain sensors are faulty but you don't always lose ABS... the steering and G sensors are ESP related rather than ABS... if you lose a wheel sensor then the whole system becomes inoperative... no ABS, ESP or Haldex (I believe)...
ESP is even switched off when certain engine sensors go down too such as the MAF sensor... ESP uses engine management to control torque request as well as the ABS system to control wheel spin...
Its all very complex but... any fault in the system will be flagged... as it is then it relatively easy to isolate the system thats at fault... the software has comprehensive diagnostics.. the number of maps you have to adjust when doing big turbo conversion for example just so that the extra load, boost, airflow etc doesn't trigger limp modes and other ECU protection systems is staggering... this redundancy and protection is built into all Bosch systems and its supporting hardware...
In VCDS when logging in the various modules you will see (if you have the labels set up correctly) the upper and lower bounds of any logged parameter... when a signal goes 'out of bounds' then a fault code is flagged... the software in all these modules also use a checksum system to ensure that no data gets corrupt... the ECU in particular checks its checksums on a regular basis to make sure that nothing has happened to the code that could (for example) cause it to misinterpret the torque requested from the throttle pedal potentially causing it to go wide open throttle as you are driving down a busy high street (the throttle pedal is completely disconnected electronically and virtually from the throttle body itself... the software determines how much to open the throttle based on the requested load from the driver... but thats another discussion entirely)
Anyhoo... the point is... I am not assuming anything... the diagnosis is based on information gleaned from monitoring the various modules and checking fault codes on the whole system... as non of the sensors are malfunctioning then logic suggests its a mechanical issue... seeing as the haldex operates hydraulically and the 'electronics' essentially operates a valve to determine how much pressure to use to clamp the clutch shut then seeing as (and yes this was tested too) the haldex does actually engage and it does have AWD when the fronts start to lose traction the only real issue is that the clutch does not fully disengage when its supposed to even when the 'electronics' have 'done' so... this suggests that the motor or the valve is sticking before it gets fully set in its 'disengaged' state...
The reason why its disengaging fully when there is no power is that there is no pressure being generated by the pump... when there is power applied then with the valve not closing properly there is enough pressure to engage the clutch slightly...
Of course there is no real way of telling until the controller is off and apart... (or replaced) but seeing as the haldex has spent a fair amount of time 'running' with no oil and what did come out of it was thick and glupey then I think its a fair assessment to say the controller is not a happy bunny..
No assumptions here...
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