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Discussion Starter · #1 ·
I've been somewhat suspicious of the function of the AWD system in my R recently as it doesn't seem to kick in quickly enough, letting the front wheels spin for a bit before it picks up grip in the rear.

Since we got some snow last night I went to a parking lot to test it out and there's definitely something wrong with it.

I had my GF watch my wheels as I floored it with TC off. My front wheels of course broke loose immediately, but my rear wheels took a good second or so before they started doing anything, and while she said they did start slipping too, they were spinning a lot slower than the front wheels. I tried to do donuts and the rear just refused to step out which has never been a problem in the snow before. I'm wondering if the Haldex clutches are shot and not transferring enough torque to the rear, but I don't know much about failure modes for the Haldex system.

Any ideas?
 

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I had this problem with my AWD when I first got my car. Some research here pointed to the DEM Pressure/Temperature sensor. It cost about $80 from Tasca and took about 20 minutes to replace with a jack/stand.
 

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Either a faulty AOC pump that is on its way out or pressure sensor solenoid, replace solenoid first. There is a way to test the pump by applying power to it and listening to the sound.
 

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Before you go throwing parts at it, get it scanned with vida/dice, there may already be some stored codes in there that will give you an idea exactly what the problem is.
 

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As was stated above, sounds like a pressure sensor. Although, if the pressure sensor isn't actually getting enough fluid pressure you're looking at the filter and pump.
 

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It was the pump. $650 installed.
Sounds reasonable, considering you have to take out the exhaust and the drive shaft in order to replace it. Did you have them drain and refill the fluid and change the filter too?
 

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I just has my awd system fixed... It would have been quite expensive, thank goodness for warranties!


2005 Volvo S40 T5 AWD M66
 

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Did they include a filter and fluid when they changed the pump?? Otherwise, the pump and dem will still have issues down the road.
 

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Huh... That's a good question. I'm not sure on that!

2005 Volvo S40 T5 AWD M66
Yep. The clutches wear, and clog the filter. The pump has to pump harder to reach the pressure the sensor wants to see, which in turn cooks the DEM and starts blowing fuses. It's a vicious cycle.
 

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Yep. The clutches wear, and clog the filter. The pump has to pump harder to reach the pressure the sensor wants to see, which in turn cooks the DEM and starts blowing fuses. It's a vicious cycle.
Oh dang... I may have to inquire with Volvo, see what they say. Thanks for the heads up!

2005 Volvo S40 T5 AWD M66
 

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I saved my own ass by resetting the temp sensor with VIDA/DICE. It was reading -50c, a temp that would thicken up the fluid too much to allow engagement. Worked for a year so far!
 

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This is a nice time to remind people to change the fluid and filter in there. This is not often done and then people complain about the AWD reliability.

Ford eliminated the service interval when they owned Volvo to lower the cost of ownership, Audis and VWs with the same system recommend filter/fluid replacements every 40,000 - 60,000 miles.
 

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Yep. The clutches wear, and clog the filter. The pump has to pump harder to reach the pressure the sensor wants to see, which in turn cooks the DEM and starts blowing fuses. It's a viscous cycle.
Fixed it for you, now it's a pun :p
 

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Fixed it for you, now it's a pun :p
But AOC fluid isn't non newtonian... It's basically hydraulic fluid... You my friend are thinking of the viscous couplings of olden times. Wherein a non newtonian fluid was in the coupler and it coupled a bunch of plates together when a difference in rotation existed.
 

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But AOC fluid isn't non newtonian... It's basically hydraulic fluid... You my friend are thinking of the viscous couplings of olden times. Wherein a non newtonian fluid was in the coupler and it coupled a bunch of plates together when a difference in rotation existed.
I'm aware that the Haldex oil is just hydraulic working fluid and the AWD engagement is software-governed, rather than relying on fluid shear characteristics as with Volvo's pre-Haldex AWD viscous couplings. It was just a pun, jeez.
 

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I'm aware that the Haldex oil is just hydraulic working fluid and the AWD engagement is software-governed, rather than relying on fluid shear characteristics as with Volvo's pre-Haldex AWD viscous couplings. It was just a pun, jeez.
I know. I'm messing with ya.
 
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