Hi!

I have a 2014 XC60 3.0 T6 with 110.000kms. The car drives and operates normally however there are two issues:

• On cold start it randomly misfires for about 5-30 seconds (not just in very cold climate but with a cold engine, although cold ambient temperatures might make it worse). The misfire is not respective to any cylinder, it happens randomly and about 3-4 cylinders are affected.
• Two times since I own the car (1,5 years & ~15.000 kms) it has thrown a check engine light both times during highway run. The associated trouble code is p0420 cat efficiency below treshold.

Extra info:

• During cold weather the car whistles on cold start, sound kind of like a flute. It usually dissapears when the idle drops down, but when it's very cold the sound remains for a couple of minutes during driving. I know this car has a whining sound on start due to the airpump, but this flute-like whistle is different than that, and it only happens below freezing temperatures.
• When the gas-tank is filled above 1/2 the car makes a constant-pitch humming sound from around the gas-tank area. It's most prominent when cruising at city speeds, or waiting at a red-light. If I kick the throttle or take it away during curising the sound stops for a while. Also warm weather makes this worse. This is not accompanied by any noticable driving problems. Runs and drives perfectly.

I'm not sure if the two problems are related. It was just at a volvo garage for regular service and they said the car is in perfect condition. However I now have an appointment to look at these issues specifically. In the meanwhile I changed the spark plugs to original OEM same part number etc. (they were pretty bad, especially the one in cylinder 6 had a lot of white-ish deposits), exepcted the rought idle and misfires on cold start to go away, but strangely it stayed the same. I then did a battery reset (just disconnected it for about 10 minutes) and voila next morning the car ran perfectly. 0 misfires. 1 day later (no battery reset this time) the misfire was back. Seems like when I did the battery reset the car defaulted a lot of adjusments that might have caused it to actually run better. Gonna do the reset and confirm the absence of the misfiries one more time!

At this point I'm kind of stuck, not sure where to look further. Of course I'll take the car to the service, but in the meanwhile I'd like to gain some tips and possibel experiences on this topic especially due to the number of threads where I read that mechanics did not really know what to do with these kinds of issues on T6 engines.

Any help / comment is appreciated.
Thanks!

 

Any resolution to this issue? I have the same car (‘14 XC60 T6 with 60k miles) with a couple of symptoms that are identical to those you described (cold start whistling and misfire on warmup). Symptoms are intermittent currently, but becoming more frequent so I’m looking to get out ahead of it. Thanks