07 XC70 jerky, then drivetrain does not engage, anti-skid light

[erikv11]

07 XC70 with 180k miles
Happened today, no previous symptoms.

TL,DR: Engine seems fine. Problem occurred in town, was able to drive it home slowly. Drivetrain slips or it disengages completely, in 1-2-3 or R. In the driveway, in D or R with foot on the brake the rear driveshaft spins in a slip-go lurching fashion. Some codes, BCM and DEM.

Transmission fluid level is good, color is a nice pink. Will have to check PO records to see if has been changed.
Axle nuts are all securely tightened.
CV axles look fine and outer CVs appear fully engaged into the hubs.
AWD was working fine as of about a week ago, seems unlikely now (see below).

Behavior when driving; have only tested at low speeds:
Drive train somehow slips in any gear tested, 1-2-3 or R. So wheels don't get full power from engine rpm. When I drive it forward at slow speed, hear a circular clunking type sound from somewhere underneath, drivetrain slips rhythmically, then finally it disengages and engine revs freely with no power to wheels. At this point the anti-skid message and the anti-skid icon both illuminate and if I stop and shift into park then I hear a buzzing type sound from up near the transmission (I think?) but when I go back into gear, F or R, it will not engage. If I turn off the car the lights go away and it usually will engage again and drive at least 20 meters or so. I left the car for a couple hours and then came back and was able to drive it 3 miles home but it was slipping the whole way. Had one fully disengaged episode there - maybe it does a little better when cool but hard to say.

Behavior in the driveway:
Start car, engine is fine, shift into D or R the car lurches rhythmically while engine idles. CV Axles don't turn with the lurch. Rear driveshaft DOES turn, in a stop-and-go rhythm that matches the lurching you feel in the driver's seat.

VIDA says:
several uninteresting codes (TPMS, park assist sensors, CCM sensor)

BCM-0095 Comminication between control units - Communication problems with DEM
DEM-000B Oilpressure faulty value

And likely unrelated (?) but also showed on first read:
ECM-9000 Brake pedal sensor - Faulty signal
ECM-614B Exhaust camshaft control - Faulty

Also in case it is relevant: drove it through a car wash yesterday.

At first I was thinking transmission problem, thought I'd reseat the TCM on a prayer, but that was before I knew the codes and that the rear driveshaft was turning with the car motionless in the driveway.

Would be great if this is somehow one of the minor DEM problems

[Krons]

In the driveway, in D or R with foot on the brake the rear driveshaft spins in a slip-go lurching fashion.

Sounds serious, hope it isn’t. Make sure I understand the statement above—the front wheels (and rear wheels) are not turning but the driveshaft is? Interesting.

[erikv11]

In the driveway, in D or R with foot on the brake the rear driveshaft spins in a slip-go lurching fashion.

Sounds serious, hope it isn’t. Make sure I understand the statement above—the front wheels (and rear wheels) are not turning but the driveshaft is? Interesting.

That's right, car is held motionless by the brakes but driveshaft turns.

I think if there was a broken half shaft I would see that one turning? Have to check again in the light but that's what I have so far, agreed it doesn't sound good.

[Krons]

I should start with Volvo drivetrain isn’t my expertise. At first I was thinking a failed AWD clutch in the rear…but makes me wonder how the transmission is letting power get to the driveshaft.

I would consider giving Steve at East University Import a call he might be willing to give a little over the phone help and what you might be into. Like most shops they’d want to look at it…not sure if you could limp it down there?

[jonesg]

I would say the haldex is not engaging because the front wheels are not turning.

raise all 4 wheels off the ground and see what turning or not.

[erikv11]

Or maybe engaging the fronts is the problem, since the driveshaft can turn while the fronts are motionless. That's why I was initially thinking front CV or axle.

The rear actually tries to engage, that seems to be why it is jerky in the driveway with the brake on. When it does that I can look under the car and see the Haldex box lurching.

Regardless getting it up is a good idea thanks, I'll be able to get a look tomorrow.

[BlackBart]

This is making sense. The rear is trying, the front is not moving. Doesn't the Haldex sense front slip relative to rear though?

So, what at the front is slipping badly? The diff? Are these limited slip at the front? If not, can one axle shear the bolts and the transaxle just spins?

[jonesg]

maybe it popped a cv joint.

[erikv11]

maybe it popped a cv joint.

My money is on this, though I half looked into it and didn't see anything. Okay, maybe 20% looked into it. Will update tomorrow!

[erikv11]

It's amazing how many ways aftermarket CV axles can find to fail.

Pics to come when I finish it up tomorrow.