DEM/Diff/ABS Issues

[Tim Duggan]

Hi there,

I've read a lot of stuff on the forum by searching but not my exact combination of circumstances hence the reason for starting a new thread. Trust this is OK.

Background - Car is a 2006 XC70 D5 Automatic AWD just shy of 200k miles. I parked it up about 8 months ago with a major steering rack leak. It had also developed a nasty rumble from what sounds like the rear diff. Originally it started around 30-40 mph and then seemed to tail off a bit above 60mph. Obviously something was wrong but I needed the car and didn't have the time or money to invest in it so I kept driving on it for a couple of months before I got access to another car, which is when I parked it up. Prior to this there was one occasion prior to this after working the transmission quite hard (towing a caravan up hill) when it threw a light - I do not remember the exact code but it was something about a solenoid. I searched this at the time and it seems to be a common fault. I cleared the code and carried on and it has not come back. I do plan on flushing/changing the ATF but need to get the fill plug out first (it is seized and seemingly made of cheese as the torx rounded as soon as I put any amount of force on it).

Fast forward to last week. I finally got round to getting the rack refurbished. When I woke it from its 8 month slumber to take to the garage, I noticed an ABS/Anti Skid warning message. The rumble was still there. To my ear, it seemed worse than I remember it. I put the error codes down to the brakes being sat still over winter and hoped a good run would clear things up. When picking it up after the rack replacement however and driving it a bit, it threw a further red code "brake failure stop safely".

I plugged it in to VIDA. I had a few steering rack angle codes which seemed to clear and haven't come back since (touch wood) however two codes come back persistently BCM0094 Communication with DEM Module and CEM1A64 Communication with AOC Control Module. I found the troubleshooting chart on here and followed that through. Fuse 23 had blown but, once replaced, I got 12v at the DEM, also 12v to the Haldex pump seemed to work (at least it made pumpy sounds). On that basis, I assume the DEM itself is faulty. That's not a problem, relatively easy fix, but I would like to try and find out the root cause. Is it just weather ingress or could there be a fault connected to the noisy diff? There seemed to be evidence of oil leakage so maybe that got into the module and caused the damage?

Here are pictures of the codes. Like I say, all bar the ones listed above (and the CCM code which I don't care bout) seem to have cleared. The battery was flat at one point as well which probably didn't help.

https://photos.app.goo.gl/X9B4HuVBTFvfmUWR6
https://photos.app.goo.gl/FEokPrSzhNhJ3Qew5

I can't do any extensive investigation on the diff as the MOT ran out on Thursday so it has to stay on my drive which is on a slope so I can't get 4 wheels off the ground. Basically I need to get it through the MOT so I can either take it somewhere with a lift or at least to some flat ground so I can get it up in the air and do some testing. What I don't want to do is spend £160 getting eth DEM refurbed to clear the warnings to get it through the MOT just to have it burn out on me again.

Any thoughts, ideas, suggestions welcome. I've found a video I made of the diff noise when it first started about a year ago here: https://photos.app.goo.gl/fa2QaM3t9LTNskeG8.

One last thing, it has also developed a bit of a hiss on acceleration, sounds like it's coming from behind the dash. Searching on the forum for this, it sounds like this is most likely a seal on the brake booster. I think the car is punishing me for parking it up for so long! It hasn't thrown a code for this and braking effort seems unaffected so hopefully this won't cause an MOT fail. I will fix it, of course, I just need to get it road legal so I can move it around a bit.

Thanks in advance.