ETM (Electronic Throttle Module)
Your mileage to failure may vary. I'm on my third one at 90k miles (more on this in a min) Usually get "Performance Reduced" message. Using ODBII reader to retrieve the code when this occurs is the best diagnostic. Early failures can be infrequent and won't occur in 2 consecutive drive cycles (each drive cycle is one engine start/shutdown sequence). 2 consecutive drive cycle detecting the same failure is required to store a code in the engine computer and turn on (and stay on) the Check Engine Light. Part + Labor is free with Volvo's 10 year 200k mile extended warranty on this part (a big thanks to Don Wilson)
However, Volvo's policy to the dealer service department seems to be that they need to have a stored code to do the extended warranty work. Infrequent occurrence during early stages of this failure may not store a code. This can be a frustrating to deal with. Having a portable OBDII code reader handy in the car allows you to read the code whenever it fails might give you more insights and perhaps valuable in convincing the dealer to fix without waiting for failure that strands you.
Click here for info on how to decode your OBDII codes.
If I were to make a guess on what the new ETM software did (Probably very few people know because it is some software source code in Sweden somewhere). I venture to guess that since ETM has multiple redundant sensor fingers (the swiping surface for these sensor fingers is what wears out. Thanks to Don's detective work again) to determine position, the new software is probably less conservative and rejects outliers through redundancy. My 01 XC is on the original ETM at 72k miles with the new software while my T5 is on its third ETM (with new software) at 110k miles. However, the first ETM was probably unnecessarily replaced because Volvo hadn't developed the new software yet. The second ETM was replaced at the beginning of the extended warranty. Volvo probably have since then learned... try new ETM software first before replacing ETM as a cost saving measure. This is what they did to my XC70 when the ETM problem showed up.
