AWD issue

[joshuasak]

Hi Matt.
I came across your website and your contributor Jimmy\'s helpful explanation of the Haldex AWD system after spending several hours unsuccessfully looking for answers to my AWD issue on my 07 xc90. Unfortunately I was unable to find my answer, but it seemed you might be the guy\'s to point me in the right direction...
I will try to keep this short... Still going to start with a little context.
I live in Hawaii, and am a decent mechanic with anything old school, and am restoring a few cars in my spare time. The newer cars I can understand when necessary but for computer controlled stuff (other than early injection) I usually look to others for guidance.
So, for the past 20 years I have been spending summers restoring an old house off grid 6 miles up a beat up dirt road in the French alps. For years I used an old Nissan with transfer case short gears locking diffs etc. But the noise and lack of AC (and my wife and kids) eventually pushed me to upgrade. A 2007 xc90 (2.5 5cyl gas, 150.000 miles) became available. A little internet research found YouTube videos of guy\'s getting unstuck with pretty much only one wheel on the ground, so I figured this would be the right car for Euro road trips as well as my mountain construction project.
I very quickly noticed that on tight steep graveled hairpins my back wheels would start spinning. Clearly the brakes were not locking the spinning wheel. So I changed the ABS sensors; that did not help. I booked an appointment with the Ferrari dealership in Monaco (only authorized Volvo guys in my area). My dusty muddy xc90 was quite out of place in a garage with polished floors and mechanics all in white; but they where super nice, went through my computer and found nothing out of ordinary. Still they had a suspicion, and recommended I change the 2 sensors located on the bottom side of the master cylinder. These were about $400 each; but I was optimistic and changed them...Nothing changed. At this point I am running out of ideas; my research indicates there is possibly a system named EBD (electronic brake force distribution) that may be controlling traction in these situations, but I am not sure if this is a component of an other system or a stand alone unit.
The vehicle seems to get excellent traction even on steep loose terrain; I will notice slight slippage (about a 1/3 wheel turn) and then full grip. But when front wheels are turned and ground is uneven, it acts as if there is an open differential between front and rear axle and power is being sent to the rear wheel with the least traction...
So that is my tale. I am not sure where the problem is coming from, and I don\'t want to keep changing components in the hope of stumbling on the culprit. Not to mention that I would not know what to change next...
Your input would be much appreciated.
Be well.
Josh on Maui, Hawaii.

[ggleavitt]

Yep, not fair to change stuff out (like two brake pressure sensors at $200 a pop). Those are supposed to require a DSTC calibration after replacement, any idea if this was ever done?

No light(s) on the dash when you start driving or when the affected wheel slips? No anti-skid messages? Nothing?

I would get the vehicle connected to a Volvo centric code reader and see what the vehicle thinks is going on. That is, in my opinion, the best first and cheapest approach.

Nice context, if you could assist with any visual indicators on the dash before or after while you look around to see if you can get something that'll read the vehicle. Think you need some peace of mind and a re-starting point.

Some good troubleshooting can be found here in the meantime- https://xemodex.com/us/diagnostic-flow-charts/

edit- remove "maybe" problem, I think it probably is a problem to have the no contact wheel spinning.

[joshuasak]

Thanks for the response.
No lights or messages... I have not done a DTSC calibration; will have to look in to that. As I have mentioned, Monaco Ferrari is the closest dealership with the Volvo equipment, and this involves basically a day trip for me.. But I might have to do that on my next trip.
At this point I guess I am hoping to come across someone who has dealt with the same issue and might have found the origin of this particular problem. The car is now stored for the next 10 months, and I will be trying to collect as much info as I can in the meantime; and hopefully get this sorted out next spring. Thanks for the link to the flow chart...It is a good reminder why I mostly keep 40+ year old cars in my shop...
Take care.

[ggleavitt]

If you have time in the next 10 months and an interest in getting closer to the nature of your reported issue, you could find a copy of VIDA (version 2014A might be the last) to load on a PC and read about how your vehicle works. Think it's still free, just takes some time to install.

In the meantime, you can see here- download/file.php?id=580 for a description of your braking system (document extract noted here- https://www.volvoxc.com/forums/showthre ... ystem-Info).

[pbierre]

Have you considered that the Haldex might be operating at its design limit? You've said "The vehicle seems to get excellent traction even on steep loose terrain". The specific case you cite is a hairpin turn going uphill. I'm not sure Haldex is going to handle this adroitly, since on a tight turn the R/L wheels are turning at different speeds. In the write-ups on Haldex, it only describes detecting a difference where the front wheels are rotating faster than the rears. Might those F v. R calculations have limits when there is big disagreement between the R & L fronts?

Then, there is the fact that the front wheels have more weight on them, and therefore on loose gravel the rears would be the first to slip when power is spilt 50/50 F/R.

Seems to me for the case you're citing, a hairpin turn going uphill on loose gravel, you would need a more sophisticated drive system than Haldex. And, in a steep enough situation, even the best traction system will slip, as it is traction-limited by the tire's grip on the driving surface.

[joshuasak]

Thanks for the feedback.
You certainly could be right... I am still trying to understand the system myself. However, I was under the impression that the ABS kicked in to slow a slipping wheel, and thereby divert power to the wheel(s) with grip. In the situation I am experiencing, it is always the inner rear wheel that starts spinning while the remaining wheels that have good contact are motionless. I have learned to not lose any speed in that section, and I get right through. But it just does not feel right that the vehicle is behaving like a rear wheel drive with an open differential.

[Masscomguru]

The front and rear diff's are open on these volvos. The ABS system steps in a little but it's not a substitute for LSD so in extreme circumstances it wont help much. It's really put in place for traction assistance in wet and and slippery road surfaces.

[xHeart]

So, for the past 20 years I have been spending summers restoring an old house off grid 6 miles up a beat up dirt road in the French alps. For years I used an old Nissan with transfer case short gears locking diffs etc. But the noise and lack of AC (and my wife and kids) eventually pushed me to upgrade. A 2007 xc90 (2.5 5cyl gas, 150.000 miles) became available.

Is family happy - cool and quieter ride?

Your issue could be wheelbase over the terrain. Look for ways to improve the wheelbase and track ratio. I would change transmission fluid, angle gear, Haldex, and the final drive fluids before the next restoring season. Change in drive style too may help.

How is front and rear suspension after 150,000 miles?