Hi, i have a europian S3, but it has similar quattro system as audi TT, so i figured to ask you (tt owners) about my problem.
My haldex unit seems to have malfunction, because it's now FULL time awd. I mean that my rear end doesn't turn off at all and it causes that when i'm doing a small speed turn with my wheel turned fully to one side, i end up having big bumps in my rear wheels (because haldex doesn't turn off my rear wheels and when i'm doing a turn, there's difference in speed of front and rear wheels). I don't understand is it mechanical problem in haldex or eletronical. Because the strange thing is that ESP works with no problem, and esp light doesn't show any malfunction. I tried looking for problems with vag-com, but it doesn't show any faults. I just don't know what to do, because than i leave the car to stand with egine off for 10-15min. it seems that haldex turns the rear wheels off, but as soon as i turn on the engine, haldex immediately turns the rear wheels on.

 

There is absolutely no way you can tell if the haldex is on or off, if it were to get stuck on the control module would disable the system immediately and there would be a fault code stored in the AWD electronics.
You either have bad rear shocks, or something may be wrong with the haldex system, its much to hard for me to tell you how to diagnose that system, so take it to the dealer.

 

i can, i lift the car's back end up and i try to spin the rear wheel, if the haldex is off i can spin it with no problem, if the haldex is on, i can't spin the wheel. i know that there's something wrong with the haldex, but i can't tell either it's a mechanical problem or there's something wrong electronically with the haldex control unit. Maybe there can be problems with the haldex oil? tomorrow i'll try to check the level of the oil in the haldex.

 

No thats the ESP activating, not the haldex. Im telling you it can be diagnosed with the VAG COM but you're messing with stuff you don't understand.

 

roll out test.

Function-test of the Haldex coupling.

- Rollout in circle

Aim: Check the function of the coupling and the response on the car. Is to be done on level ground.

1. Drive in circle with minimum turning radius at a speed of about 10 km/h.
Disengage the clutch and close the throttle.
Let the car roll to full stop.

2. Drive in circle with minimum turning radius at same speed as in case 1.
Disengage the clutch and run up the engine to 3000 - 4000 rpm.
Let the car roll to full stop.

* If the coupling is working the car will stop in about half the distance in case 2 compared with case 1.

* If there is no difference in the two cases there is a malfunction of the coupling. The problem could be caused by the coupling or by missing signals from the car. A further inspection has to be done to be able to determine the cause of the malfunction.

* If a noise from the HLSC is noticed when turning or driving in circles the oil in the coupling is damaged. The damage can be caused by overheating or by water in the oil.


- AWD test on car lift. (all wheels free to turn.)

Aim: Check the function and the control of the coupling.

1. Pull the handbrake.
Disengage the clutch.
Start the engine.
Put the gearbox in 2:nd gear.
Let the engine idle.
Engage the clutch.

* Engine is supposed to stop when the clutch is engaged. (HLSC controlled as in handbrake start.) If engine do not stop, disengage the hand brake immediately. Otherwise there is a risk of seriously damage on the HLSC.

2. Disengage the handbrake.
Disengage the clutch and start the engine
Put the gearbox in 2:nd gear.
Let the engine idle.
Engage the clutch. At least one front wheel and one rear wheel is supposed to turn.
Pull the handbrake for 2 seconds.

* Front wheel is supposed to turn while the rear wheels are supposed to stop when the brake is pulled. Engine is supposed to run all the time. (HLSC controlled as in handbrake turn.) Don't exceed the 2 seconds or repeat the test for more than 5 times during a 5-minute period. Otherwise there is a risk of seriously damage on the HLSC.


Trouble shooting on HLSC

- Visual inspection

Aim: Check for leakage and external damage that affects the function on the HLSC. Is to be done with the car on a car lift.

1. Check for oil-leakage from the coupling. If leakage is found, check oil level at the level screw on the left side of the coupling.


2. Check wires and connecting sockets.

T8 - Socket between car and control unit
T8/1, Red = Ign.
T8/2, Black = Gnd.
T8/3, White = BLS
T8/4, Blue = HBLS
T8/5, Brown = K-line
T8/7, Blue/Grey = CAN low
T8/8, Blue/Orange = CAN high

T2 - Socket between control unit and feeder pump
T2/1, Yellow = Pump 1
T2/2, Yellow/Black = Pump 2


- Signals

Aim: The following signals from the car affect the function of the HLSC. If one or more of the signals is missing or false the function of the HLSC will be reduced.

Bremse 1; BLS, BTS, ABS
Bremse 3; VR, VL, HR, HL


Auditech79 is right though, if the Haldex unit senses any problem, it won't activate, so getting stuck in FWD mode is possible, but locked into AWD not so much.

 

Please tell me you have that saved and didnt write all that from memory....?

 

Ha, I wish.

I can, without hesitation, recite the VIN from my 180 TT, and it wasn't a conscious effort to learn it.


TRUUC28N8Y1061015

And that car is long gone.

(BTW, if anyone wants to carfax that and see if that car was ever resurrected, or whether it was trashed, that'd be cool)