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Try sending for repair to circuitboardmedics.com. $1500 + $50 return shipping up front. They will open it up and repair if possible. If not will refund everything except the $50 shipping and return to you. Mine was not repairable and they contacted me and did exactly as promised, refunded and shipped back. There are a couple of other places that do the same and even have repaired for sale but their reviews were mixed. Also if all else fails call Nacarato Trucks Parts in Franklin KY or World Wide Equipment in Knoxville, TN. Ask for Ryan in the service department and tell him I referred you (Carl). World Wide had me one in less than a week. Cost was around $2500 programmed with core. BTW yours probably suffered same fate as mine. Seal on back of ECM failed and water and oil got inside.

Neither Good Sams Roadside Assistance nor Coachnet will tow an HDT IF it is tandem. They will tow a singled HDT. Others will say they have been towed tandem but I spoke to higher ups in both companies and got the above information. As Rick says, get it in writing, not just verbal. That is from experience with Good Sams.

Update: Problem solved after much needed and appreciated help from Chet. Turns out I could get my truck specific schematics from Volvo eMedia for free. The setup to give power to cigar lighter, cab, cb, and door/dome lights involves the battery low voltage protection system and two relays. Working together they shed load to make sure you can still start the truck. In my case, the R44 which is an expensive, double coiled relay was bad but my friend, Chet, had one in his stash of old scavenged electrical parts. HOWEVER, after replacing the relay, still had no power. Turns out in dissecting the schematics a fuse 52 allowed power to one side of R21. I had previously checked all my fuses inside and at battery so was stumped but when I re-examined panel I found F52 missing. Apparently the dealership in trying to diagnose my ECM problems had removed it (why?) and not replaced it. New 5amp fuse and everything back to normal.

Depends. Usually around 15 mph if I recall and usually just enough time to get you off the interstate, maybe to next exit. The whole concept is to keep from tearing up your engine. If it can’t communicate it thinks worse case scenario. Now low coolant sensor will shut you down completely in about 10 seconds. If that pops up, get off the road immediately.

13 years ago I started the same search for the “perfect tow vehicle “. Lots of advice and initially thought a Volvo 670 singled short was the answer. As you can see, I ended up with a Volvo 780 with tandem axles and haven’t regretted that choice one bit. It’s not a daily driver but have used it to go just about everywhere we needed in a pinch…groceries, restaurants, even medical clinic. A very smart individual convinced me to stay tandem because I didn’t know the future of what my truck needs would be. As many have said, choose what YOU feel will fit your needs now but be cognizant of future needs also. It is likely as time goes on more and more HDTS are going to need to haul vehicles other than Smart cars. You’re at risk of overloading axles if not carefully planned…consider that. I am registered in Tennessee as a MH…I think number 4 to do so. My county had no clue how to do it and like most bureaucratic agencies said I couldn’t (cause they didn’t want to admit they didn’t know how). After a lot of leg work, phone calls to Nashville, I walked in with a stack of papers and letters and asked to speak to my County Clerk personally not an underling. She asked what I wanted, told her, offered the ream of documents. She got that “deer in the headlights “ turned to one of the underlings without even looking at the papers and said “make this man happy.” I am. Finally when you register be sure it’s right the first time. Number 3 before me got it wrong in Nashville and it was a mess to get re-registered as a Motorhome. BTW, as I said, don’t count on DMV, County Vehicle Registration etc. to give a definitive answer. My stack of papers had copies of federal and state statutes and memos to prove I could do what I wanted.

Agreed. My recent ECM troubles and present electrical problems have been “enlightening “ to say the least. Thank heavens we have some very smart people that are willing to help when we have issues. Please share what you learned. I think the worst “sin” for any forum is for someone to ask a question then never respond if the information provided helped OR what the final solution was when solved. We all learn that way. BTW we have stayed at Fern Lake Campground in Paducah, KY. It was nice and had a really good Mexican Restaurant across the street. Also stayed at Duck Creek in Paducah but it was in more run down section of town and had a big auto salvage right next door which made it unattractive l

I’m not going to help with any advice but will definitely sympathize with you. When my ECM went out I got all kinds of funky codes and communication errors. It took a shop with a computer and $6k to get it running. I know that is depressing but as rickeieio says “We pay to play”. BTW did you find a suitable campground for longer term?

Vern, I’ve heard some good things about Grand Ole RV Resort in Goodlettsville. Never stayed there ourselves. Where are you staying now? There is also a KOA near Goodlettsville. Inside the beltway will be expensive.

Got it. Sorry you’re having issues.

Ok going back to truck tomorrow. I used a 12 volt battery at home across A & C (which I think is 85,86) and got nothing. No clicks and no energizing 30, 87, or 87a. That makes me think the coil is bad. Normally my cigar/12 volt power sockets are energized even with the truck turned off so I was thinking that this was a normally closed circuit between 30 and 87a and that since it was battery protection, as voltage dropped, something would trigger 85,86 to shed the 30/87a load which is the sockets, cb, dome and door lights. Am I thinking wrong? I can use the same battery and will put 12 volt on 30 and should measure it on 87a correct? If my hypothesis is correct then energizing 85,86 should make that 12 volts disappear? So I can also energize 85,86 to test.

Pins are lettered clockwise from red probe A,B,C,D, and E center. Will be testing socket on fuse board tomorrow to see which positions are energized.

Think I’ve narrowed my search down to a bad relay. Sent pictures to my “expert “ and awaiting his opinion. Thanks to everyone’s help and lots of Google and YouTube seems the battery protection relay modulates power to cigar/12 volt sockets on dash and overhead, CB power studs, and dome/door lights…all things not working in my truck. Took this and several relays home for testing. It is a Volvo specific five pin relay and stands taller than the others and mine has a yellow sticker with part number. It’s expensive at over $100 to replace, hence, waiting on second opinion. This relay has lettered pins not the usual numbers (and typical proprietary goods) NO diagram on it. I even peeled back the yellow sticker. However, it looks like a typical five pin configuration with A (85?), B (30?), C (86?), D (87?), and E (87a?). When I tested resistance across what I think is 85/86 got no reading. My understanding is the coil and resistor should give between 50-150 ohms. Additionally 30/87 and 30/87a both read 75 ohms while 87/87a read 142 ohms. Not sure I understand that. Would seem if it was “normally closed” in either 87/30 or 87a/30 there should be minimal to no resistance. Also the 87/87a reading points to both being close with some type of resistor in those circuits. I’m not smart enough to figure this out so any help is appreciated.

This weekend took the truck and trailer on a few day trip to Crossville, TN for some maintenance work. Had four new airbags put on and antifreeze hoses, reservoir, and liquid changed. I use J&K Truck repair and have always been very pleased with their work and prices. They called me a few hours after the truck was in the shop and wanted to show me something. Apparently on the Volvos the ram air intake hose to the turbo and the lower radiator hose are in close proximity. Somehow a rock had wedged between the hoses and rubbed both hoses paper thin in an area about the size of a half dollar. Either hose could have given way. The air hose would have just been power loss but the radiator hose would have been a catastrophe with immediate shut down. May want to periodically crawl under the truck and look around…something I haven’t done in a couple of years.

Kevin, I can reset all mine off of the steering wheel stalk under diagnostics IF they are inactive. Are you not able to do that? Should be described in your owners manual.

Thanks Dan.

Chet was kind enough to send me several schematics. Unfortunately they aren’t for my truck. Fuses and relays don’t fit what’s on my panel legend. Anyone have schematics for 2006 Volvo VNL 780? Specifically tracing no power to cigarette lighters and CB studs. Or if anyone knows where I can purchase would appreciate it. Should mention Resource Guide Schematics are what Chet sent. I don’t have a relay 29 which is supposed to control power. This is my fuse panel legend.

Ok. Sorry. This ECM stuff is all new to me.

Vern, May not be helpful but make sure you don’t have an air leak at the primer pump/secondary fuel filter manifold. When they replaced my ECM they found a crack in mine. It’s probably been sucking small amounts of air for a while because now truck idles smoother and seems to run on the road smoother. BTW careful with who you send your ECM to for rebuild. I highly recommend Circuit Board Medics. They charge $1500 to rebuild plus return shipping. If they can’t rebuild will refund full amount minus shipping. They communicated with me and couldn’t rebuild mine. Refund was processed same day.

They are coming through.

Thanks Chet and Rick.

Anyone have access to a 2006 Volvo 780 electrical schematic? I just got my truck out of the shop replacing ECM and reprogramming. Discovered I have no power to cigarette lighters or CB radio. Checked fuse and it was good at panel. Also checked fuses at battery and they are good. Isn’t that power direct from battery?

Phil, I thought you were just honest to a fault. Never tacky….well almost never. 🙄

Thank you. Yes, I’m up and running again. My ECM also could not be repaired. It had leaked water and oil into it and fried the board. A known issue with the Volvo D12. I had even replaced my harness years ago to help prevent it but the sealant had several gaps which had allowed the leak. Don’t know how you could check for that without removing and inspecting every few years.

Meds and intestinal functions are just the tip of a big iceberg, Rick. We can discuss that more if you want? 😂😂

Last update 🤞🤞. Truck out of the shop. Turned out to have no other issues besides the cracked primer pump/secondary fuel filter housing and a dead ECM. Actually the 20 mile drive home seemed like truck ran smoother and shifted smoother than before but probably just my imagination.