Just bought a 2005 CTT with the PB3 Advanced Technology Offroad Package. It's got 139,000 miles but based on it's condition I doubt it's ever seen a day of dirt roads.

I was testing the offroad setting and when I push the lever forward the 3rd time the red light for the rear diff lock comes on for a couple of seconds then flicks off. After that, if I push the lever forward again it doesn't come on at all, not even if I turn the car off and restart. When I come back the next day I can get the light to come on again but once again it turns off after a couple of seconds.

The hydraulic disconnects for the sway bars work perfectly though:-)

Anyway, as a wild guess I'm thinking the rear diff has never been used and the solenoid or whatever device is supposed to engage it may be "sticking" or hitting too much resistance from lack of use and then disengaging without completing its task.

Anyone had this problem? Any suggestions for inexpensive ways I might be able to get it working?

 

It should be throwing a code if there is an issue. But, there is an electric motor on the rear diff for the lock. I had one on my 06 Touareg, and it went bad resulting in the rear diff not full disengaging. I think that motor was around 500 bucks, and it's a pretty simple DIY. You'll also need to get the rubber seal (few bucks), and do a fluid flush since you'll lose fluid when you pull the motor off. It's just 4 external bolts and unplugging the harness. The motor is about the size of a soda can, and it's hanging off the diff on the driver side. The new diff motor was different than what was on my treg, so they either updated it, or they switched manufacturers for some reason. It seems that motor failing is more common than you'd think. You don't see it much on the cayenne side since it's a rare package, but it's pretty common on the treg side. That's all I got for ya. I don't have any part numbers, but just remember paying about 550-ish after the fluids, motor, and seal.

 

Oh - and the fluid for the rear diff is different than the normal fluid. So, don't just get 75W90. Make sure you get the fluid made for the locking rear diff.

 

Thanks, that is excellent info! You've made my day:-)