Budget M3

On Friday night, about 600 miles into our 4th of July roadtrip, I was cruising up I-25, cruise control set at 80mph. In the mountains of northern New Mexico, I used the Tip to shift into 5th while climbing a hill. Upon approaching the crest of the hill, I hit the Tip again to shift back to 6th (like I have done HUNDREDS of times before). All of a sudden, the engine revs outrageously, then the transmission gives a very loud CLUNK. I've heard missed shifts at the track, and it sounded like the trans missed a shift! Cruise still set at 80, the transmission reverts back to 5th gear and will not change out of 5th--automatic mode, tiptronic, neither works. Since I still have a quarter tank of gas and am still 80 miles from the nearest small town, I keep going in 5th--cruise still set at 80.

I exit the freeway and cruise straight into the nearest Chevron station without stopping. Stop the vehicle...the transmission readout on the dash now says D3 (3rd gear). I shut down and refuel...hoping against hope that "rebooting" the trans will clear the fault and I will be on my way....WRONG! After RTFM, I find that my trans is now in "limp mode", and I am to get to my nearest authorized P-dealer as soon as possible. I am 200 miles from Albuquerque and 150 miles from Colorado Springs with a serious mountain pass ahead of me (where there is no cell phone reception).

I call Roadside assistance and they choose to tow me to CSprings. Tell me to keep all receipts since they will reimburse me up to $150/day for expenses due to my interrupted trip...small consolation...

So here we are 3 days later and the P-dealer just called me to say that my Cayenne is ready to be picked up. They cleared the fault and "everything works fine now". The tech thinks the problem is because I had the cruise on and was using the tip at the same time--WTF!! where in the manual does it say not to do this? ...and oh, BTW, I've been doing this since I bought the vehicle and never had a problem before. So now I am about 800 miles from home, and I don't trust the damn thing.

Anyone ever heard of such a fault? Is the tech giving me a load of BS, or is this really possible that the cruise control is not to be trusted with the TIptronic?

Comments welcomed...

amaist

Shouldn't shifting the transmission manually (via Tiptronic) disengage cruise control?

If it does not disengage then it should account for that state.

ltc

Yes
No
S/W error between the DME and TCU.....it's on the 'things to do list'
I'm done.

mjw930

I agree with amaist, using the tip should disengage the cruise.

If it's in cruise why are you using the tip? I'll assume this is the V6 and you feel it's easier on the motor to use 5th for the climb but I would suggest that the trans should select the lower gear if the rpm's drop too low so let it do it's job the rest of the trip and you should be fine.

You now know what not to do so if you feel the need to drop down a gear disengage the cruise before you do it and you should be fine. No reason to not trust the car IMHO.

LVDell

Budget......so, any update? I have to admit, I hesitated when I wanted to manually downshift during a cruise control session

Likemystoppie?

A lot of cars with manual transmission's won't disengage the cruise when you down shift. Remember, the Tip isn't 'exactly' an automatic transmission. Thus it acts like a manual.

ltc

If it has a torque converter, I'm pretty sure it's an automatic transmission.

amaist

Huh? Can you name some of those cars?
If it does not disengage cruise control when the clutch is disengaged then it will just rev to redline.
Most simple cruise control units are mechanical and only work on the throttle.

Recent cars with fly-by-wire gas pedals have completely electronic cruise control systems. It's pretty much just some additional code in the engine computer. Having a disengage state after detecting clutch pedal use is trivial to implement.
I am almost certain the Cayenne has a computer throttle.

ltc

Yes, the Cayenne is eGas.....and they sometimes hesitate.

Budget M3

ltc: thanks for the insider knowledge...very helpful...


Yes...V6. When cruising in pure auto mode, the trans either shifts CONSTANTLY up and down which is not only annoying, but also unnecessary, or it waits until rpms drop below 1500 (which with the V6 has you losing valuable momentum and up to 15mph depending on the size of the hill/climb--e.g. cruising at 80mph...begin hill climb...speed drops to 60-65 before the auto kicks down from 6th to 4th at which time you begin accelerating again up to 80mph...a simple shift into 5th at the appropriate time will maintain speed). That's why I used the Tip. Since the throttle is eGas as ltc noted, the cruise stays on--which is actually quite convenient when climbing mountain passes on the interstate/freeways in rural areas with little or no traffic.

Now that I know what's going on, I guess I only have two choices when using cruise--1) manually disengage cruise before using the tip, or 2) leave it in auto mode and be annoyed with the constant shifting or not shifting. The only other alternative is to NEVER use cruise when using Tip which is very annoying since I've gotten used to it up to this point...

Thanks for all the inputs...I'm still on vacation and will repost again after the return trip home...

Budget M3

Don't do it, dude!!! ...especially if you are 600 miles from home!!!

LVDell

Needless to say......I didn't

ltc

Go ahead......touch the button.....you know you want to.

If I still had 'that vehicle' I'd be glad to try it....at least a couple dozen times for you......but sadly, I no longer have that vehicle 'that we don't talk about'

LVDell

I'm tempted but it's not quite time to press the button.

User 4221

I've done it a few times on my '05 CS with no issue. Count myself lucky.
Advance the cylinder, lock the hammer...... Pray there's no round in the chamber.