2005 XC70 DEM/ECM problems?

[WRSFL]

I just bought a 2005 XC70, and about two weeks after purchase I was taking off from a light, and the transmission thunked into high, the gearshift indicator went to a dash, and I lost the AC, tach, temp, and trip computer outputs. I couldn't shift manually, and had no warning messages or lights. Shifting into neutral produced another loud clunk, and when going back into drive another thunk, and I could take off in an obviously high gear. It has done this several more times, in increasing frequency. The check engine light did finally come on, then this morning when approaching the dealer it did it again, and this time lit the ABS light, and virtually every warning light.

Shutting the car off and restarting it always restores all functions.

The dealer cleared all the codes, drove the car for 8 miles and couldn't duplicate the problem. I got in to leave, and it did it within 100 feet. They checked the codes again, and they say I need the DEM and ECM (for $3800). And will probably need to replace 3 other computers as well, which would have me investing more in the repair than I did the car!

I've located the two components through XeModex for far less, and replacement doesn't seem too hard. My questions are these:
Is it likely that both units are bad, or could the DEM be causing the ECM code as well?

Is it possible or probable that the ECM, if bad, could damage a new DEM?

I'm running short on time to work on this, as I should be taking this car on vacation in two weeks, and if replacing both is the cure I can live with it but I'd certainly love to save $595!

Any input or experience appreciated!

[oragex]

This kind of issue is so often described on forums, I start wondering if it's not the same car (of course it's not).

First thing I would do, if the car was bought from the dealer, I would cancel the transaction. This kind of trouble can be difficult to fix, and most owners sell their vehicle at that moment.

Otherwise, having the dealer look at the car at this moment is similar to leaving the house door wide open and going to job. They will rip your credit card without any shame AND you will not get it fixed. They are only at the beginning of a list of replacement parts. They know what the issue is, because it's very typical, but they will replace several parts, because now it's when they make money.

This kind of issue can be related to the CEM (under the dash), that can be fixed by Xemodex. I would ask them their opinion, and what part could be in cause. It's a component that causes a digital communication issue with the main computer, resulting in the symptoms you are describing.

[doublebug]

yesterday looked at a car like yours. When the issue reproduces car cannot be started until you remove 2 ABS fuses. A guy went to us after ABS module repair. We disconnected all modules but CEM on the hi speed CAN and still could be able to see the wrong signal on the green CAN bus wire. Next Friday will do further and try check CEM, wiring connectors etc. ABS is active module on the CAN bus so when you disconnect power all other modules have more time to send messages via faulty bus and car works better.

[jimmy57]

The high speed network connecting the ECM, DEM, ABS, TCM, SWM,and CEM is going off. WHen that happens the transmission has a default mode with high fluid pressure and limited gears.
It is HIGHLY unlikely to need an ECM and a CEM both.
The 8 mile test drive with no fault and then it gets started and fault sets is a scenario describing a DEM failure from heat. The DEM is close to exhaust pipe on the all wheel drive unit at rear of rear driveshaft.
The fault codes in the car would be telling as to what kind of problem you have. If shorted network wiring codes are set then that is the cause and modules are not likely involved. When network goes down for any reason a lengthy list of communication codes set in several modules whether the fault is a module or a wire fault killing the network.
Unplugging the DEM and using the car to see if it has an episode would be one way to see if it is the DEM. You will have a warning message on dash from the DEM being unplugged while you drive and will have no AWD function but it could let you know it is the DEM if no faults occur and the DEM is plugged in again and the fault occurs again.

[WRSFL]

I think it's a good call on the CEM, guys. Now that I've had some time to do some reading the DEM seems to fit with some other funny little things, like taking off in the wet the other day with extended front wheel spin, and an almost imperceptible "twitch" at highway speed now and then which I now am interpreting as something in the AWD.

I spoke to an incredibly helpful Tony at Xemodex yesterday and got some insight on the CEM failure scenario, and what I'm going to do is test the pump this morning, do a visual on the DEM and CEM, and send him one or both of the modules for testing and repair. At this point I fully expect the DEM to be bad, and on replacement I'll put that shield from ipd on, as that seems like cheap insurance for the heat as well as physical damage from the ample road debris we have in FL. I may get lucky on the CEM and only need to pay the bench charge for testing.

I understand that there has been a SB on the CEM water intrusion problem, so I can see if that seems to have been performed at the same time.

[abscate]

Two weeks from purchase? Check your states lemon laws before you spend more money/time.