Hello all, I've been browing this forum for the last 2 years I've owned this car but I'm making a post about some concerning behavior in my 2007 XC70.

Earlier this week I activated the winter button and all hell broke loose. Brake failure light, traction control service light, transmission service light, and the DIM went crazy. I pulled the car over, restarted it and it would idle but the gear indicator just showed a "-". I got towed out of the snow bank I was no stuck in and limped the car back to the condo I was staying in. Later that night I tried the car again, CEL was now off but the traction light was on. I drove the car for about 2 hours afterwards and that light went and stayed off until tonight. I have driven approximately 600 miles since this incident.

Now 5 days later I was driving, ironically enough, to AutoZone and I got the Traction Control Service message, about a minute later I got a brake failure warning. After this my gauges, especially water temp, went haywire. Tac and Speedometer were both in and out, and the brake light failure would flash on and quickly go away. I parked it, shut it off, and started up again. The transmission would shift into all 4 positions but the light indicating the position stayed in Park and the gear indicator just has a "-". All the same stuff that had happened after pushing the Winter mode button earlier this week. Additionally, I got an immobilizer warning when I was scanning for the codes, but this has since gone away. I was already on my way so I limped it to AutoZone and pulled the following codes:

U0002 - High Speed CAN Communication Bus Performance
P0863 - TCM Communication Circuit
P0700 - Transmission Control System (MIL Request) - not sure what MIL request means
P0600 - Serial Communication Link

All the "P" codes are listed twice.

I drove the car home and it seemed very sluggish. Almost as if it was starting in a higher gear (like Winter mode would do) and it was making a non-rhythmic tapping sound underneath the radio area. Upon arriving home the car idles fine, but still throws the brake failure warning, when stopped, and in park, very strange.

All this started after pressing the W button 4 days ago. The car has been fine the last 3 days (roughly 600 miles) I've been driving it and doesn't really have any precursor showing when this will occur.

The car is a 2007 and has 147XXXk on it and has been 100% fine up until now. It has had some weak starts as of late, but the battery is a year and half old. I've read about people with similar issues and most suggested to disconnect the battery and then see what happens after that. I did this last night and there were no changes, I also checked voltage and that was fine too as that was another suggestion I saw.

Any guidance is helpful and I thank you all in advance for giving this a read.

 

I would start by clearing all codes and verifying that you have a good 14 volts at the battery with the engine running. Why you have seems to be a low voltage issue.