Powerseat and aircon intermittent

[Mr Bagshaw]

Hi, I have a problem with my 2002 xc70. The powerseat and aircon are intermittent. I can make them work by taking out fuse 24 and putting it back in but this only fixes the problem for a short time. The fuse does not blow and the instrument cluster does not have a problem and works as it should. Any thoughts and suggestions greatly appreciated.

[billr99]

I would suggest a VIDA scan to see if it picks up anything that might connect the two systems for this. Each system is controlled by a different CPU which might say that it isn't those but might point to some common power feed problem or similar.

Just as an example, over the last year and on both my P2s I had a "power system failure" CEL come up, pointing I thought to either the batteries (both were oldish) or the alternator (both original). In each case, VIDA didn't help all that much so in both cars, the alternators and batteries were replaced with no joy ultimately. In both cases, the cars eventually got to the point of a failed to start, wherein VIDA finally indicated a failed fuel pump control module (PFM). Seemingly unrelated failure and the only thing I can figure with it was that the circuit boards in both failed PFMs were heavily corroded with that corrosion somehow producing the "power system" message.

So I guess I'm telling you is to get a VIDA scan but be prepared to do a bit of digging to find out the ultimate cause.

Good Luck,

Bill

[Mr Bagshaw]

Thanks Bill, much appreciated. Yes I was afraid that there would be some pretty serious digging to do. Can you recommend any VIDA scanners for the home tinkerer that doesn't entail selling my entire family?

[billr99]

Thanks Bill, much appreciated. Yes I was afraid that there would be some pretty serious digging to do. Can you recommend any VIDA scanners for the home tinkerer that doesn't entail selling my entire family?

Not really. I'm an old IT guy so I just used an old Dell laptop I had laying around and made a dedicated VIDA scanner out of it. VIDA isn't hard to do if you start from scratch and put nothing on the laptop otherwise. I don't even allow it to hook to my network or do any updates above the basic install of Win 7. So if you can do that much, its not a bad deal. As far as the DiCE interface, I got mine from China years ago so I'm not sure what the new version are like. Perhaps someone who reads this can add their two cents on that subject.

Cheers,

Bill

[BillAileo]

I went the same route as Bill and everything went great for quite a long time until I absent mindedly updated the laptop. Do not do that unless you want to revisit the entire process.

[pbierre]

Have you tried cold-rebooting the entire car system? This works with home computers that slide into a glitch, and it works with cars too where the problem is not hardware.

Turn car off at least 5 minutes.

Disconnect battery negative terminal cable. This kills power to everything except the security alarm (which has a small battery).

Put the ignition key in position "II".

Reconnect the battery, taking care to keep a solid contact while tightening bolt.

Leave ignition in "II" position for 2 minutes - time enough for all modules to reload sw from flash and reboot.

Car now ready to startup and test. Reset clock.

[Mr Bagshaw]

Thanks everyone. Will have a play with it at the weekend.

[Mr Bagshaw]

Just tried the cold reboot but alas the seat and aircon will only work for a bit. Its odd, if I turn ignition off, remove fuse 24, turn on ignition and then off again replace fuse all works again for a while.
Got to say and this may not be the forum to say it but this sort of problem does make my 1984 Mercedes w123 wagon and my 84 Range Rover more appealing.

[billr99]

Just tried the cold reboot but alas the seat and aircon will only work for a bit. Its odd, if I turn ignition off, remove fuse 24, turn on ignition and then off again replace fuse all works again for a while.
Got to say and this may not be the forum to say it but this sort of problem does make my 1984 Mercedes w123 wagon and my 84 Range Rover more appealing.

Not to worry. There are days that I wish I was back in my '93 RR LWB instead of having to delve into the brains of either of my '05 Volvos. Might have gotten crap mileage but it started and went in all weather including -40C.

Cheers,

Bill

[Xfingers]

Are you the only one who drives the car? Hopefully you can get the seat into a position that's comfortable and leave it there.

I'm not sure why your aircon is intermittent. Some people have had mechanical problems with the clutch on the pulley being worn and fixed it with the "bread clip" method. You can search on it for more info but you seem to suggest it's an electrical problem.

When my 02 was on the road, the DS power window worked intermittently. I could always get it to work if I turned the engine off but left the key in position 2. Never got around to cleaning the switch and electrical connections.

[MacNoob]

The power seat module also contains the temperature sensor for the A/C. I believe it's located under the seat. It may have a poor connection due to corrosion/age. I did have to have one replaced on my '07 fairly early in the car's life to fix an issue with A/C&heat not working properly.

[hoonk]

The power seat module also contains the temperature sensor for the A/C. I believe it's located under the seat.

I'm not aware of a temp sensor under the seat, there is one behind the small grill in the CCM on the dash for the inside temp, one in the evaporator for evaporator temp, and one in an outside mirror for outside temp. (there is actually a sensor in each outside mirror, but only one of them is for the climate control)

[MacNoob]

I haven't looked at the block diagram for ACC, but I know that the driver's side power seat module was replaced on mine to correct an issue with ACC. Makes sense to me that for dual zone to work, there needs to be some kind of sensor on each side of the car.

[hoonk]

I haven't looked at the block diagram for ACC, but I know that the driver's side power seat module was replaced on mine to correct an issue with ACC. Makes sense to me that for dual zone to work, there needs to be some kind of sensor on each side of the car.

I agree that makes sense and There used to be 2 temp sensors with the 850s, a left and right temp sensor that were in the ceiling near the grab handles (there were little fans in each of those, sucking air past the thermistor), then Volvo changed to the 1 interior sensor being in the CCM (with a little fan pulling air in)

[hoonk]

The power seat and aircon are intermittent. I can make them work by taking out fuse 24 and putting it back in but this only fixes the problem for a short time. 89438944

Looking at the attached wiring diagrams for the PSM and CCM - note that fuse 24 powers the relay marked 2/29 in position cmi22. That relay powers both the CCM and the seat module. (don't know what else it powers.) Perhaps you simply have a bad/erratic relay on the CEM (central electric module)

On this diagram is the position of the possible erratic relay on the CEM for the seat module and the CCM.

8945

CMI22 is the 3rd one down from the top on the right column - try swapping that one with almost any other relay in those two columns (most of them are the same, match the part numbers) and see if your problem is fixed ( and possibly have something else stop working if the relay is bad!) Be sure to mark the relay you take out of position cmi22 so you don't forget which one was (possibly) bad.

[Astro14]

I was thinking "CEM" when I first read this...and the fact that the relay controlling both resides on the CEM makes me more confident in suggesting that you likely need a CEM.

Xemodex. $600. Not cheap, but they do quality work.

I'm about to replace the CEM in my 2001 T5 because of the odd indications that I am getting...all of which come through the CEM...

[Mr Bagshaw]

Thanks for all replies. Will have a fiddle when I get a mo and report back.

[Mr Bagshaw]

Thanks for that but sadly I still haven't got to the problem. I also have a 2004 xc70 (with working seat and aircon) and tried removing cmi22 to check that it powered the seat but it appears not.
I also tried removing the relay either side of cmi22 to see if perhaps I had it wrong but still the seat worked.