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Dem communication problems

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Old Apr 1st, 2018, 20:05   #11
Mick82
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Hi been under car today checked voltages I've got 2.8v on can high and 2.2v on can low and 12v to pin 1. But now it's saying anti skid temporarily off. When my original unit went down I found a chart to follow to determine weather the pump or dem had failed I put 12v to the pump and that worked and the chart led me to the dem being faulty.
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Old Apr 3rd, 2018, 10:12   #12
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Quote:
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Hi been under car today checked voltages I've got 2.8v on can high and 2.2v on can low .
Not sure how you have measured these voltages nor what they signify.

I basically worked out that if there was power to the DEM, the pump could be heard to start any issue with the Haldex unit was either the DEM controller, the pressure switch, or the the solenoid.
The solenoid I checked out using a 9v radio battery. A member on here lent me a known good pressure switch to substitute, which then left the DEM as the prime suspect despite being given a clean bill of health by BBA.
The unit was rechecked by Lucus, found to be faulty and a recon unit supplied. Plugged straight in and worked out of the box.
One thing I did have was very dirty Haldex oil. I had oil stored in glass jars which had 1" of sediment in the bottom after 24hrs standing.. I "changed" oil well over 6 times before I noticed an improvement in the quality.

Good luck

Cheers
Bob

Cheers
Bob
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Old Apr 15th, 2018, 08:06   #13
volvo for ever
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4 wires at the dem 1x 12v power .1x earth 2x can wires they should be around 2.1v and 2.7 v dont worry if a little higher ie 2.3 or 2.8v if you have these readings then wiring okay

ive seen this twice where both pump and dem went down so replacing dem only wont cure you need to replace pump too also when replacing pump remember replace filter

regards.
for future reference you can actually donnor dem but not sw it and see if that erases codes
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Old Sep 8th, 2018, 05:03   #14
pumpkinhook
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Default 2004 XC70 AWD Issue

I have read this thread (and others) and tried the suggestions posted to resolve my AWD not working. I say that it is not working as the driveshaft rotates when front wheel lifted & rotated, all wheels spin when all off the ground, but when I stomp the accelerator from standing start - the front wheels spun, nothing from the rear tires, slip indicator flashes.

I replaced the differential filter, pump, & fluid. Same tests as above, same result. I even replaced the pressure sensor (from junkyard).

I went through the DTS codes: DEM stated "Not Started" and did not change during a test drive. I have not checked voltage to the DEM via the harness connector (tomorrow morning), fuses are good. Does the message "Not Started" mean that the DEM is bad (if voltage present at the connector)?

Thanks.
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Old Sep 18th, 2018, 12:28   #15
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I have read this thread (and others) and tried the suggestions posted to resolve my AWD not working. I say that it is not working as the driveshaft rotates when front wheel lifted & rotated, all wheels spin when all off the ground, but when I stomp the accelerator from standing start - the front wheels spun, nothing from the rear tires, slip indicator flashes.
1) Front wheel off the ground and front to rear drive shaft rotating is normal behaviour. Its when the front wheels are on the ground and the drive shaft can be rotated you have a problem, but not at the DEM but the angle gear or collar drives.
2) If you can prove the pump is good by use of a 9v radio battery, the oil in the DEM is clean, the solenoid can be seen to operate again using a 9v battery, the "fail" points are basically down to two items - Pressure switch or DEM failure.
I have read instances of both.
However,
the DEM unit is located in an exposed position and appears to be susceptible
to water ingress. I would get your DEM checked out before spending more money, and if you intend keeping the car get a DICE/VIDA setup.

Good luck

Cheers
Bob
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