2008 V8 Blowing Passenger Compartment Fuse #11

[RickHaleParker]

I chased-up the shipping status of the Vida/Dice knock-off (VXDIAG VCX NANO), and apparently they are on back-order.

Lately there have been a bunch of Chinese vendors that try to pass them off as a U.S. based vendor. Long delays in getting it to the buyer because it the product location is falsified. I detected one that should be delivered today. That eBay vendor is going to get his 100% positive feedback destroyed. It was suppose to of been located in Orlando, FL.

[marcels]

I knew the week was going to be busy, but I really thought I'd have gotten a chance sooner than today. Nonetheless, back on it.

⦁ First I checked the total resistance with key in 'II' position, and it was at 0.8 ohm.
⦁ Went straight to the CEM and disconnected both connectors. Resistance jumped to 378 ohm.

Looks like it's the CEM.

Next question is whether I dare opening it up and searching for the bad component? I suspect one of the soldered-in relays will be the culprit, but I am unaware of any schematic that covers details of the CEM component functions, so I'd be working blind. Anyone familiar with the relays, and more importantly, which would be connected to the ignition switch in the 15l terminal (only terminal that is active only in the position 'II' ignition switch configuration).

If you think I'm off on a tangent, let me know as you could save me going down a senseless rabbit-hole.

Thx, Marcel

[marcels]

So I pulled the CEM, considered the consequences of something going wrong when attempting to open the "Chinese puzzle" of a case, and went for it.

Definitely not a task for the impatient, since there are numerous plastic tabs to be released, and since the case consists of three parts, it leads to each being trapped by the others. Then just as you're making progress with the tabs they tend to re-latch...F*%K!!!

Once apart, there was clear evidence of water intrusion as evidenced by white corrosion spots...nothing extreme, but possibly the root of the problem. In one place a track appeared to have experienced arching (2nd image). I cleaned the boards using electrical contact cleaner and a toothbrush. The track that appeared to have experienced arching looked fine afterwards with no damage to the circuit board track.

The plan is to reinstall the unit and see what happens. I'd feel better if I found something definitive, or better yet - if I had identified which of the Tyco relays fed fuse 11C/11 and replaced it as a matter of course. Nonetheless, I don't want to blindly order all the relays and remove/install replacements. I'd think that's what the folks at XeMODEx do all day long...along with QC testing.

Thanks,
Marcel

[ggleavitt]

Xemodex is great, they do a thorough job.

Real question in my mind is how did the CEM get wet in the first place and what can you do to prevent this from occurring again? MY08 has the revised wire harness plenum cover over the CEM (pre-05 P2s had a 2-piece cover that sometimes leaked) so you should not have had water ingress with the CEM, even with clogged drains. Before this is all over I might have a close look at the cover and the drains below the perforations at the rear of the hood, see if everything is clear.

[marcels]

ggleavitt, don't get me wrong, I'm not disputing that XeMODEx are great, nor did I intend to criticize the service they provide. I have no experience with them and therefore not qualified to comment in that manner. I was simply stating that as an upgraded CEM remanufacturer, I would expect nothing short of them but to replace all electromechanical relays with new equivalent or upgraded units regardless of whether those in the "core" unit were functional. In my opinion, it just wouldn't make sense for a remanufacturer to leave the wear and tear of electromechanical components to chance, and then stand by a one year warranty.

BTW, retail cost for all nine relays (TYCO/NEC) would be just over $50, so that is one of the options I may consider if I become convinced the issue resides within my CEM. XeMODEx "Module Program Transfer" would be another, as it involves swapping out my CEM for a "fully remanufactured and upgraded CEM" with my CEM's programming transferred to it (cost $599 plus shipping). I don't see the point of the $389 repair service for my situation since I'd want my unit fully refurbished and not simply the current issue resolved. I also intend to speak with my local dealer and see whether they would offer a program transfer service, as I know that I can purchase a brand new CEM from a dealer for under $700. In the meantime, I'm still hoping the gremlin to be elsewhere in the vehicle.

Regarding how water may have made its way into the CEM, that is a good question. I began to suspect the sunroof drains since the cowl drains were clear and my '08 also has a one piece cover, and all the rubber boot material was in good shape with no signs of cracking. We've experienced some severe flash-flooding in the area over the course of the past few weeks, which has no doubt highlighted a vulnerability in the seal/drainage system which will need correcting.

GENERAL UPDATE:
I reinstalled the CEM after cleaning it. I then cleared the memory of all the systems by disconnecting the battery and connecting the positive and negative cables leading to the battery together for 30+ minutes.

⦁ I then reconnected the battery and measured the resistance across the ground-side of fuse 11C/11 to ground --> 0.8 ohms...the
CEM cleaning changed nothing.
⦁ I then disconnected the lever-lock connector "B" in the cowl area (long 32-pin connector furthest from driver fender) --> 0.8 ohms.
⦁ Reconnected connector "B" and disconnected connector "C" (short 36-pin connector nearest to driver fender) -->64 ohms!!!
⦁ Kept connector "C" disconnected and also disconnected connector "B" -->383 ohms
⦁ Reconnected connector "C" (only "B" disconnected again) --> back to 0.8 ohms. THIS SHOWED CONNECTOR "C" TO BE THE
SOURCE WITH REPEATABILITY
⦁ Reconnected connector "B" (everything now reconnected) --> 0.8 ohms (I as begun)

Interestingly, I went through the same process early-on in my troubleshooting, but even though the fuse had blown the total resistance was 1.8 ohms. Also, I don't recall there being such a dramatic change when I disconnected both connectors "B" and "C" at that time. Unfortunately I wasn't all that confident with what I was doing at that time, so perhaps I made an error or misses a reading. I do however recall the resistance changing over time, so there may have been some time-varying behavior going on at that time, confusing me even more.

For now I'm back to studying the wiring diagram to plan my next steps for disconnecting components attached to connector "B" to see what causes the drop.

Thanks,
Marcel

[marcels]

ISSUE RESOLVED!!!

After some methodical troubleshooting I chased the issue down to the TCM, and in particular, a couple of chaffed wires in the harness close to where it plugged into the TCM. The blue/red wire was grounding onto the transmission case. The white is a communications wire.

Thanks to everyone who offered suggestions!

FYI, in the process of weighing-up what to do if the issue proved to be the CEM, I received the below reply from the technical support team at XeMODEx:

For the CEMs, yes the relays are all replaced during our remanufacturing. Any component that has a high failure rate is replaced even if it's currently testing okay

...exactly what I'd expect from a quality remanufacturer.

Happy motoring!

[ggleavitt]

That's great, congratulations on finding the root cause.