Hi, my name is Robert and I live a couple hours north of San Francisco. The person I live with recently got a multiply used, 1999 Volvo V70 XC from a Volvo enthusiast. The car has some "Courtesy Electronics" issues that need to be diagnosed and fixed. I have a high-tech background from way back when, but have never done much in the way of car repair, and never on a Volvo before, so I have a few questions about how it all works.

 

what specifically is going on? I'd start by checking fuses and testing bulbs etc if those are out. Volvos have multiple fuse boxes and route some circuits through a device called the CEM (central electronics module) which has embedded relays etc. These CEMs are prone to cracked solder joints and may need to be replaced or rebuilt. You may also need to inspect various connectors and clean them off to get a solid connection. Good news is older models like you '99 don't need special programming should you need to replace the CEM.

 

Hoonk,

Thanks. If it's all analog circuits, that makes it much "easier". (I had been getting indications that it was something fancy like a LIN or CAN system -- one less layer of things I need to learn about.)

I'm still looking for (a good readable copy of) tp3938202:

I spent a few hours yesterday searching for a copy of Volvo document tp3938202 online but couldn't find any. The most frequently cited source, VolvoWiringDiagrams.com, has disappeared (and been coopted by some domain name, etc. sales scam). The only hard copy sources I saw are out of stock on that item. There are a couple of links to old eastern block country (??) sites, but they are not in English and could easily be a good way to get a computer virus. I chickened out on those in the end, but someone who speaks the language might be able to safely navigate them.

I was given a hard copy of the followup 1999 document, tp3941202 (more or less late 1999 corrections/modifications to the system -- or something like that) -- it contains the main engine stuff and all the main wiring harness maps, but omits the "unimportant" supplemental system stuff that I need including the pages that define the supplemental part codes. (I do have the tp394202 page that defines many of the main part codes "upstream"). I was able to find lots of free copies of the tp394202 PDF online and snatched one with clear images of the diagrams. I also grabbed an earlier (1998, tp3932202, moderate legibility) wiring diagram in case parts of it apply (or someone else needs it and it disappears).

I have a request in to the former owner of the vehicle in case he happens to have a copy of the document you recommended, tp3938202.

If you or someone else happens to have one (and/or a higher resolution image of the diagram you posted for central lock), I'm at "rc" + "blasdell" + "7" [at yahoo dot com]. (Not sure I'm allowed to say that here. Let me know if I'm not. I did try to buy one.)

And if anyone can simply explain what all the diodes are for (how and why they are used) that would be a help. Are they there just to kill reflected voltage pulse waves, or do they form some sort of sneaky "one-way" RC circuit with inductive or capacitive components in switches, light filiments, solenoids, etc.? Never seen them used this way, but I see online articles about adding them to doorbell chime circuits to make them ring longer (and some kinds -- Zeners? -- do get used as "active" resistors where you use the I(V) curve to figure out the response if I recall my 30 year old electronics class correctly) At first glance they don't seem to be part of a logic circuit. Of course, the wiring diagram isn't what I recognize as a proper circuit diagram, so I'm not yet sure what I'm looking at and what isn't shown.)

Thanks,

And sorry about the slow message turn around time. I'm new to Volvos and car maintenance, and live in a very rural area of West Sonoma County, CA. The internet works only 75% of the time, and I sometimes get dragged away by local VFD calls, etc. May take me a few days to read through stuff. I do very much appreciate the help (and all the videos that are available which will also take a while to peruse.)

Robert

 

Have you looked at eBay for any CDs with Volvo VIDA software? there may be some theftware out there with wiring diagrams and part numbers. You may be able to get the repair manual software without needing the diagnostics licenses which shops pay the big bucks for..

 

MT6127:

What specifically is going on: I'm afraid it's quite a long report -- see below. (It has been useful for me to write it out. You may not have time to read it all.)

Ok on the CEM. Will learn about it and look for it. Will also look into Volvo VIDA software CDs.

(And a former JPL lead mechanical engineer said that in spacecraft, the diodes are often put in just as electrical gates to protect sensitive computer components shared power supply from feedback from the associated electro-mechanical mechanisms that they control. Often they have 1000s of them. Maybe that is why they are present in the wiring diagrams and car. I forget how diodes fail -- if they do under normal circumstances.)

-----

What's going on?

Simplest version: it's complicated and I'm not sure yet -- someone else was working on the V70, a few last items got too complicated, and it got dumped in my lap (until he has more time). I'm new to Volvos, rarely work on autos, but am in the end quite good at sorting through complicated electrical and mechanical issues if I'm given time to learn or recall the fundamentals (and time to work on the problem). It's my girlfriend's car, it's new to her, she's driven it maybe 5 times for a total of 60 miles or less, and she is (alas) not a careful or reliable witness of mechanical phenomena. The previous owner has changed lots of stuff back and forth, but no one was keeping notes. I witnessed a small portion of it. The previous owner is talking about getting someone to overwrite the chip programming to fix the courtesy light problems -- which just feels off/extreme/quite possibly wrong and a source of who knows what other future issues, so I'm trying to find some time to systematically work through things first... I had been led to believe that all the power systems and relays checked out, but that may be a missimpression. (Oh, and re-reading, I realize "Hoonk" said it's not going to the onboard computers anyway in a 1999, so it that's true, messing with the chip programming would be not good.)

If I had to bet after a preliminary looksie with a DVM, and now that I've been told by "Hoonk" that the courtesy system is all analog, I'd guess that there is a better than 50% chance that there is a power supply problem somewhere "upstream" of the driver door. (I was getting DC voltages of 100-200 mV between leads at the end of the cable to the gas cap door pull-switch. Have no idea what the circuit is, but shouldn't that be closer to 12V? Should really run an insulated wire to the battery ground and recheck. Tried the door metal, but it was all well painted so I just checked voltages between leads.) Maybe a relay is sort of working and so some systems have just enough voltage to sort of work and others don't? Not sure I believe that, but seems not inconceivable and an early place to start systematically looking if I start at the battery and work toward the switches.

The Previous Owner did fix up things under the hood, got it smogged, and the engine reportedly ran well and still does. (I've driven it maybe 1000 feet, so I'm taking that as probably true, and suggestive that half of the electrical system is working fine, including most of the on board computer functionality.)

The problem is that the vehicle had (and still has) some convenience safety issues. (We live 45 minutes from the nearest gas/service station on rural coastal highway 1 in CA, and the girlfriend works at night, alone, in a remote state park.) The gas gauge does not work, the courtesy and door warning lights are malfunctioning under certain conditions and would drain the battery if left enabled, and now the gas cap door won't open any more. The handle right next to it,,to pop the tailgate door, also doesn't work now -- I thought it did before, but I just can't recall. And now the car thinks the driver door is always open. More specifically, and in correct time order:

1. The front driver-side window was partially "off it's tracks" and moving very slowly. (I suppose the motor strain could have damaged a power supply component upstream causing some problems below. Seems like I read something about that somewhere. I somewhat acidently have the window back in it's tracks/clips/ whatever, and it now moves promptly and correctly. I watched a video on it for a different door or model year, and want to go ahead and just replace the old clips while I have the door opened up. Need to get the parts, and need to play around to find position for access to the front clip -- the one that was loose. It is now somehow back holding the glass, but I've never actually seen it yet. I easily see the rear one, and it looks old/deformed but still in one piece. Just need to play around a bit. (Had to stop part way through looking at it the other day.)
2. The front passenger-side door was damaged years ago. The hinge needs to be rewelded (it clicks/catches badly). Everything else about it seems to work, suggesting (?) no electrical wiring damage there. The previous owner has a local mutual friend to weld it for us sometime. Or I've got a friend with a MIG welder if need be.
3. The rear passenger-side door was jammed shut with the 1"x3" red edge warning light continuously on (so a battery drain threat). The previous owner fixed it for us, and it seems to work fine now with no apparent damage (?) to the wiring. (I'm just saying that since something is currently wonky, and something is getting overlooked. He did a fine job with the door.)
4. The driver-side manual "on" switch for the roof dome courtesy light (up by the top of the windshield) has been and still is intermittent/screwy, though somewhat less so than it used to be months ago. The driver-side dome light worked fine in response to various door openings, etc., when the toggle switch was set to the middle/door position. The Previous Owner has a replacement unit from a junk yard, but we don't know what is going on, and we don't know that the replacement is fully functional. It hasn't been installed yet. (The girlfriend needs the dome lights to work as a security feature when she is getting in the car at the park in the dark.) This seems innocuous enough, but might be a sign of something deeper going on. Don't know yet. And now the car thinks the driver door is always open, so all the courtesy lights are always on if the toggle is set to the middle "door" option.
5. We brought the car home, and it sat for 1-2 months (waiting for a title snafu to get sorted). We started it and let it sit idling half an hour to recharge the battery, etc. It started effortlessly and ran smoothly. The coolant was overfilled and some boiled over (irrelevant I think). The next day, the battery was hyper-dead. (When disconnected and after sitting 12 hours it still had a voltage of< 1 V DC, implying seroius permanent damage. It was also way beyond warranty. I got a new one.)
6. With the dead battery removed, and the ignition key out, I went through all the circuits at the Supplemental Fuse Box (SFB). All circuits had "infinite" resistance except for Circuit 15 which had about 2.3 ohms resistance. The back of the SFB lid identifies C15 as: Courtesey lights, Door warning lights, Trunk/cargo space light, Seat belt reminder, Glove compartment light, RTI = Road and Traffic Information System. At 12 V, that 2.3 ohms correspond to a 4.8 A (57.6 W) drain. (I'd guess the lights are all old incandescents, so I imagine that resistance would go up as they light up -- don't really know, but the value seems in the ballpark of what might be normal. Was just having to guess at it to get started.) The resistance wasn't "solid" -- it floated around a bit suggesting that contacts are a bit old and oxidized -- but it was raining and a bit awkward with the DVM so it could have just been my clumsliness too.
7. I pulled the fuse for SFB-C15, put in the new battery, and started the car. The engine and everything worked fine except, very slowly as I recall, I began to hear the bloody chime going off ad nauseum. It could be the volume has been the same, but it also could be that it started weak and got stronger with time (wonky behavior). Not sure now. It was raining, and it was all new to me as it wasn't my car.
8. I put SFB-C15 back in, restarted the vehicle, and got in the back seat and played with all 4 doors and viewing angles until I satisfied myself that the warning lights only came on for the door that was open, and that the driver door's red edge warning light was always on and was at least part of the battery drain problem.
9. It might have additionally been that the girlfriend also left the headlight switch in the middle running light position when she got out and left it overnight only to find the car dead the next day. Don't think so, but just to be safe, I reset that tiny flat screwdriver head option switch next to the headlight switch to the 45 deg CCW position so as to disable all the daytime running light functionality (so the running and/or headlights don't get left on and somehow kill the battery).
10. The car was taken back to the previous owner's local shop, he replaced the radiator (which was slowly leaking), and tried to replace the driver door latch mechanism with a part from the local salvage yard, but ran into difficulties, and ended up putting the old one back in. He spent all day on it, and ran out of time at the end. Afterwards, the door key no longer turned the lock mechanism (but the key fob does) -- so the thing isn't quite seated correctly (I watched a video on it). Also, the gas cap door (whatever it's properly called) stopped working. It had recently been replaced, but was -- I thought -- working well. It doesn't "feel"/"sound" like anything is happening electrically when I pull the switch. Could be the solenoid or whatever is jammed, but betting it's not getting power.
11. The previous owner wants to have a second go at replacing the latch with the "new" part. I want to see what's up (or not) with the SFB-C15 electrical sub-system first.

That's it at the moment (I think). Sorry for the posting length.

And thanks for any suggestions. Probably be at least several days before any updates.