No communication with DIM or DEM, BCM and REM intermittent

[Tightmopedman9]

2003 XC70

Been trying to troubleshoot a problem on a friend's car. He bought it without a functional DIM, but otherwise the car seemed to function fine. Occasionally the DIM would kick back into life while driving. I re-flowed all the solder connections on the DIM and it started working for a few weeks more frequently than it had before. Now, only the check engine light will work on the DIM.

Yesterday we tried to determine why the AWD was not working. Using VIDA we found that the DIM and DEM were offline. The DEM is getting voltage at the module, and I tried a known good DEM module, which did not fix the problem. 

We tried swapping in a known good used DIM of the same part number, which did not work. After trying the DIM swap the car was stuck in no CAN mode, with the transmission staying in 3rd gear. Pulling the battery cable did not remove it from the mode, but after clearing codes it started shifting. 

Sometimes, after pulling the battery cable the BCM or REM will go offline. 

I swapped in a new CEM by swapping the EEPROM chip containing the immobilizer code, and also changed all relays on the CEM. This did not resolve the problem either. 

I'm looking for what other areas I can check, as right now I'm not sure what else to look at. 

[boxpin]

On my 05 xc90 everything pointed to the BCM. I was about to replace it then stumbled across Xemodex's troubleshooting flow chart. Turned out to be the CEM. I sent it off and two days later the car was 100% restored. The problem sounds like a power loss. I know this may not help at all but worth a look to see if they have a flow chart that helps identify the problem. 

http://xemodex.com/us/diagnostic-flow-charts/

[Ihatespeedbumps]

I think we have two separate issues here. The BCM and DEM operates on the high side of the network and the DIM operates on the low side. The only common thread here is the CEM which has high and low side communication. 

I think fault tracing with the Xemodex flow chart posted above is a good start for the DEM. What fault codes were originally stored? Do you have any experience swapping EEPROM's onto used CEMs?

[Tightmopedman9]

I'll run through those flowcharts tomorrow and report back.

I didn't pay much attention to the codes thrown as there were probably 50, and each one was a faulty communication/signal missing code. I'll take a look at the codes again tomorrow and try to group them by high or low side.

Replacing the EEPROM on this CEM was the first I had done, but I have a decent amount of electrical background and am confident I did it properly. It seems unlikely to me that the CEM is the problem, since swapping CEMs did not change the problem at all. I backed up the EEPROM so now I can clone as many as I need, although it might be best to invest in a chip clamp so I can re-program the chip in-situ. 

[hootie6828]

So, not sure on the DEM issue, but the DIM has to be programmed to the car, if it's not, it will not be on the network, and only the CEL will light up.

[laird]

There is a good reason that Xemodex has a fix for the CEM:(

[Tightmopedman9]

Shoot forgot to respond to this.

The problem was partially due to my fault. The replacement DEM I installed was from an '05, which has a CAN bus communication speed of 500kbps, double that of the '03 at 250kbps. This triggered network wide communication errors causing other modules to drop off the network.

After putting the stock DEM back in and more troubleshooting it looks like the problem is just a bad DIM and DEM.  

Xemodex states that the DEM is not swappable, but I'm going to try swapping in another '03 DEM and see if that resolves the DEM error. If not, he'll send both units into Xemodex. 

 

 

 

[Ihatespeedbumps]

Thanks for the update!