4 wheel drive not working

[paul gray]

Have had a new haldex filter fitted and new oil but still only front wheels working,any suggestions much appreciated. the car is 56 plate xc90.

[S60D5-185]

It could be many things and having the codes read with VIDA for something like this would help enormously.

It will pinpoint the fault and save you from wasting money guessing

In the meantime:-


Have you checked to see if the haldex pump is working OK by unplugging it from the DEM and using an external 12v power supply? You should hear it running if it is still working. If it can be heard running when checked the DEM maybe faulty or the fuse supplying power to it blown.


Secondly have you checked that the propshaft cannot be turned by hand when lying underneath ( engine off )?

If you grip it by hand and you can revolve it, the spline in the angle gear is U/S.

[paul gray]

there is a 1A64 code coming up saying communication with DEM signal missing.

[XC90Mk1]

Originally Posted by paul gray

there is a 1A64 code coming up saying communication with DEM signal missing.

The Haldex unit presses the clutch plates together this driving the rear wheels however the DEM is on the side and contains both a pressure sensor and temperature sensor. It sounds like a fault code has been registered here.

Be a little careful as my 2012 version listed the DEM as a fault and yet it was actually the Haldex unit itself.

I think logically you have 2 steps. Firstly ensure that the error has been cleared correctly and secondly replace the DEM module (I don’t believe people pull out the temp/pressure sensors individually).

I have little knowledge of the DEM as I had the Haldex unit replaced however the DEM is separate and if it is reset and flags up I think I would be looking there.

[S60D5-185]

Well that's where you need to start looking. Who read the codes and with what?

I would hazard a guess that the full code is CEM 1A64

[S60D5-185]

Originally Posted by XC90Mk1

The Haldex unit presses the clutch plates together this driving the rear wheels however the DEM is on the side and contains both a pressure sensor and temperature sensor. It sounds like a fault code has been registered here.

Be a little careful as my 2012 version listed the DEM as a fault and yet it was actually the Haldex unit itself.

I think logically you have 2 steps. Firstly ensure that the error has been cleared correctly and secondly replace the DEM module (I don’t believe people pull out the temp/pressure sensors individually).

I have little knowledge of the DEM as I had the Haldex unit replaced however the DEM is separate and if it is reset and flags up I think I would be looking there.

Yes they do.


When I had a fault code Dem 0007 ( AWD not working) on my previous XC70 it was the pressure sensor within the DEM at fault.

I obtained a new pressure sensor from Volvo and replaced it. Pretty easy job as the access is good and no special tools at all needed.

This guy has a different code to the above but I certainly wouldn't replace the DEM unit at this stage as it may not be faulty.

[Shadeyman]

Could be a worn Bevel Gear, its easy to check..

The simple way to test the AWD is to reach under the car and turn the drive shaft to the rear axle by hand. If it turns freely somethings wrong (probably a worn Bevel Gear), if the AWD is ok you should not be able to turn the drive shaft more than a couple of degree's".

[XC90Mk1]

Originally Posted by S60D5-185

Yes they do.


When I had a fault code Dem 0007 ( AWD not working) on my previous XC70 it was the pressure sensor within the DEM at fault.

I obtained a new pressure sensor from Volvo and replaced it. Pretty easy job as the access is good and no special tools at all needed.

This guy has a different code to the above but I certainly wouldn't replace the DEM unit at this stage as it may not be faulty.

That’s handy to know for the future, cheers!