C70 transmission slippage and hard/delayed shifting
 

I purchased a 2007 C70 with 99k miles just under a year ago. I did have the car inspected and was well aware of the transmission issues and the car did have some minor downshift issues between 2nd and 3rd gear when I bought it. Otherwise the car was immaculate and exceptionally well maintained.

The car was already significantly discounted (IMO) and I used the inspection report to knock another $1200 off the price. I've driven the car for roughly 20,000 since I bought it with varying transmission issues. Shortly after purchase it threw a service transmission urgently warning and I took it to my mechanic (not Volvo specific but very good) and he replaced a knock sensor and the car ran great for about 2500 miles before slowly reverting back to a pattern or great driving for 100-200 miles and then progressively worse slippage until the "urgent transmission service" triangle and check engine light reappear.

The car drops into limp mode and then after it's been parked the triangle disappears but the check engine light stays on. After roughly 100 miles of driving the check engine light goes off and the car drives normally for another 50-200 miles before the cycle starts again.

What is unusual (at least I haven't seen it here elsewhere) is that the the triangle of death is often preceded or followed with a "low bulb failure" and once with a "stop lamp failure" warning??

My mechanic has been very hesitant to recommend anything further since he feels that it's as likely as not to be an issue outside of the transmission itself.

I did notice a thread here where is seems that the electric throttle body (do I have that right?) was sending a code to the transmission generating a transmission warning and limp code??

The car runs great and the transmission works perfectly about 50% of the time. I love the car and have no issue spending money on a rebuilt transmission if that is actually the issue but I have a hard time believing that a genuine transmission related issue would be so intermittent.

Any thoughts on the best way to proceed would be greatly appreciated...

Have you checked the transmission fluid level and the color of the fluid? You should also see if there's any stored coded (ie transmission overheating can push you into limp mode). A quick fix would be to do a series of drain/fills on the transmission to see if that smooths out the shifting can manages the temperature better.