2008 V8 Blowing Passenger Compartment Fuse #11

marcels · Post by **marcels** » 07 Jun 2020, 16:06

Hi all!
My wife's '08 XC90 V8 suddenly lost all power while she was driving along the highway. Everything suddenly died: engine, electronics, dash. She doesn't recall what message was displayed since it caught her by surprise and her primary focus was getting off the road safely, which she managed perfectly.

She called me and after spending a half hour or so checking the obvious things, I determined that it was too dangerous to diagnose roadside, and called AAA to have it flat-bedded home.

The bottom-line is that fuse #11 in the passenger compartment was blown. Replaced it and vehicle fired and ran fine, but blew once again few miles into testing. I'd purchased a cache of 7.5amp mini-fuses, so was able to replace and limp home. Since then I've been testing resistance between ground side of the fuse to ground while disconnecting the various systems on that fuse: Switch airbag passenger side, Antenna ring/ignition switch lighting, and a goulash of essential 3-letter abbreviations - SRS, TCM, ECM, CEM, REM.

Worth noting at this stage: I DO NOT OWN A VIDA/DICE SETUP, but recently ordered a budget alternative, the VXDIAG VCX NANO for Volvo with VIDA 2014D. That has yet to arrive. However, when I attempt to pull codes using my BlueTooth ODB2 adapter/Torque software, it lists no faults.

Using a DVM, I found that the resistance before the fuse blows is around 1.2 ohms, but drops to 0.5 ohm once the fuse blows. Unfortunately I have not been able to witness the resistance change in a meaningful way when I unplug the various components I have found the connectors to. Having said that, I was unable to get to the TF-80SC transmission's TCM, since it is difficult to get to mounted on top of the transmission (unlike the other models which have it in the engine compartment along with the ECM).

I am also questioning whether the wiring diagram I am using is pointing me to the correct locations, and whether the connector I am disconnecting is the correct one. A perfect example if the SRS, which the wiring manual shows is housed within the base to the center console. However, when I remove the console, the large connector beneath where it slides in doesn't appear to go to an SRS module. Likewise the alleged location for the passenger airbag switch, indicated to be within the dash endcap panel on the passenger-side (vehicle right side; opposite place where the passenger compartment fuses live), includes no such switch, but a terminator plug of some sort.

So what to try next? I await my cheapo VIDA/DICE knock-off in the hopes some codes emerge. But otherwise I am out of bullets. I read in the below post that moderator RickHaleParker has a handle on CEM relays that may need addressing...

viewtopic.php?t=86076

...it sounds like I need to solicit the wiring-master's skills, having
done what I can with the DVM and with visual/mechanical inspection for frayed wires.

I'd appreciate any advise fellow forum members may have to offer.

Thanks!
Marcel

Post by **RickHaleParker** » 08 Jun 2020, 02:09

marcels wrote: ↑07 Jun 2020, 16:06 I am also questioning whether the wiring diagram I am using is pointing me to the correct locations, and whether the connector I am disconnecting is the correct one.

Which wiring diagram are you using?
1.2 ohms to 0.5 ohm between which two points?

marcels · Post by **marcels** » 08 Jun 2020, 10:38

Hi Rick, and thanks for your reply.

I measured between the top terminal (spade?) of the #11 fuse (bottom is hot) to a ground-point on the drivers rocker area after having pulled the trim surrounding the lower door area. I can get you a ground point number later this evening, but essentially between the power feed post-fuse #11 to ground, which as I understand should be the total (parallel) resistive load of all the circuits on that fuse.

Thanks!
Marcel

marcels · Post by **marcels** » 08 Jun 2020, 10:40

...sorry, and the wiring diagram is the "VOLVO V70 (-08) & XC90 WIRING DIAGRAM 2008" (TP 39113202).

Post by **ggleavitt** » 08 Jun 2020, 13:18

Fuse 11C/11 feeds the ignition switch (3/1) and in turn provides direct power to the CEM (4/56) as well as to the airbag, SRS, REM, and antenna ring. The ECM and TCM get their power from the CEM (pins C:5/C:14 and B:20 respectively). This is all noted in the EWD. VIDA also has a very good description of all the pinouts for CEM. See "Product Specifications/Specifications Electrical/Electronic/372: Signal description, central electronic module (CEM)" when you get your copy of VIDA working.

I'll suspect that you have an issue with ignition switch and/or the CEM but that's just a guess at this point as based on your reported symptoms.

Happy if it's something else, maybe a code scan from your reader (when it arrives) will add some detail.

Post by **RickHaleParker** » 08 Jun 2020, 13:40

TP39113202 is the Volvo official EWD.
The fuse is 11C/11.

Switch airbag passenger side, XC90
Supplemental Restraint System module (SRS), XC90
Transmission Control Module (TCM), XC90
Engine Control Module (ECM), XC90
Central Electronic Module (CEM), XC90
Rear Electronic Module (REM), XC90
Fuses in spare fuse holder, passenger compartment XC90
Antenna ring/ignition switch lighting, XC90

Yes the resistance measured is the TOTAL resistance of everything between the two points.

Normal value when the generator (GEN) charging: 13.0 - 14.5 V.
14.5V/ 7.5A = 1.93Ω . Total Resistance should not be less then 2Ω.

Disconnect branches and watch for the total resistance to rise above 2Ω. That will give a clue to what is drawing a lot of current.

Post by **ggleavitt** » 08 Jun 2020, 17:20

"suddenly lost all power while she was driving along the highway. Everything suddenly died: engine, electronics, dash"
"Replaced it and vehicle fired and ran fine, but blew once again few miles into testing". So it runs for a bit then pops the fuse.

Sort of points to a device short versus a mechanical short unless there's something that's missing from the description. Pretty much everything that feeds directly from the 11C/11 fuse is electronic in nature so all the items in the last post are absolutely valid and the REM is a prime candidate to check.

How to troubleshoot now becomes the question if the scenario continues. If this ends up being something that you can replicate over time, a hair drier on the suspect module may help the problem to present more quickly otherwise I'll hope your codes provide more insight. Once you're able to read the vehicle, please post them.

marcels · Post by **marcels** » 08 Jun 2020, 19:34

ggleavitt, what you reiterated is exactly what happens.

Thanks everyone for your feedback. It's great having interested, knowledgeable folks like you to lean on!

It's difficult for me to spend much time during the week, but hopefully tomorrow night I'll re-run the process and note the resistance at every stage of component disconnect and post.

I chased-up the shipping status of the Vida/Dice knock-off (VXDIAG VCX NANO), and apparently they are on back-order. I now wish I'd gone with a different option, although I suspect the majority of non-Volvo units are likely China-sourched, and may even be shipping from off-shore.

I'll post my figures once I re-test.

-Marcel

Post by **SuperHerman** » 08 Jun 2020, 20:55

Not sure on your year/model - but on a 2002 XC70 I had after much searching and even a CEM repair from Xemodex; I found my problem to be a failed shunt related to the DIM circuit. It would cause the fuse to blow and take out everything downstream.

So, if your year/model is similar (they updated the CEM at some point) it would not hurt to check the relays and shunts. If someone has the correct wiring diagram they can look up the offending circuit and see if any relays and/or shunts are involved.

You can also download VIDA, without the DICE tool, and just use the diagram and part portion of the program.

If you can get the correct part numbers for the relay and/or shunt you can try swapping them with a like part number on the system or source them new or from a wrecker. I bought a bunch off a car on Craigslist for a few bucks - you just need to make sure the part numbers are the same.

It is unclear whether the car still dies when the fuse blows from your post.

Post by **ggleavitt** » 10 Jun 2020, 07:11

For 2005 onwards, new version of CEM and REM:
• Faster (new processors), more robust version, higher quality and lower production cost.
• Higher speed on the CAN high-speed network – now 500 kbps, previously 250 kbps.
• All diagnostic communication between VADIS (now VIDA) and the car takes place as before via the CEM but now
only via the CAN high-speed network. Introduced due to legal requirements.
• There are no longer any "loose" relays in the CEM or REM – reduced risk of contact problems.
Several relays have been replaced by FET transistors and other relays are soldered within the CEM and
REM. Consequently they cannot be replaced separately.
FET = Field Effect Transistor.
• Main responsibility for alarm functions has been moved from the CEM to the REM.
Alarm activation causes are therefore now read from the REM.
• The CEM now has two connectors. One connected from the engine compartment and one connected
from the passenger compartment.
• New adapters are required to connect the CEM and/or the REM to the break-out box.

Cut/paste from a very old document but 2005 marks a turning point for the "hub" modules, management codes change as well.