Highbeams work low beams don't 2001 s80

joesauris · Post by **joesauris** » 25 Feb 2018, 11:05

Like the title says, I have an issue where the lowbeams won't work, dispite replacement but the highbeams do work. For a couple weeks, at least the left low beam would come on which bought me a little time on the issue, but now both low beams don't work...well to clarify, the left low beam comes on at ~50% of the time, but not under my control. Now i'm in the akward position of having to use my high-beams at night, unless I'm lucky and then I can go one-eye'd with the low-beam (if you call that lucky).

I've read a little bit of other posts and it looks like a potential culprite might be the relay on the CEM which is located under the steering column somewhere? Sounds like a pain but not the end of the world, I just wanted to get some veteran input before I start taking things apart. I need this car so I can't afford it being "down" for more than a single weekend. I was particularly concerned by the idea that the CEM would have to be reprogrammed by Volvo? Is this correct or did I misunderstand? Is any general relay replacement good or is it a volvo specific relay?

I also read up a bit on the headlight switch, which apparently was recalled in other models but not the s80. Furthermore, the highbeams won't come on if the headlight switch is in the off position, which leads me to suspect the switch is fine.

Any advice would be greatly appreciated. I've worked on subaru's but not volvos, just to say I generally feel capable of getting the job done, I just want to be confident that I'm doing the right job

joesauris · Post by **joesauris** » 14 Mar 2018, 06:59

Anyone?

Post by **SuperHerman** » 15 Mar 2018, 23:08

Check your fuses and relays. I had a similar problem on an XC70 which ended up being one or the other.

Post by **RickHaleParker** » 16 Mar 2018, 07:12

There are no headlight relays.

The Central Electronic Module (CEM) powers the headlights but the light switch module (LSM) instructs the CEM when to turn on the low beams.

The only place the left and right low beams are not common is the lines from the CEM fuse box to the headlights. Start with Fuses F22 and F23 of the Central Electronic Module and trace to the Headlights.

It could be as simple as the fuse is flaky, not making good contact or corrosion in the connection.

Click two time to read the images.

Post by **SuperHerman** » 16 Mar 2018, 12:33

You may be correct on the relays, it has been a while since I worked on my 2002 XC70 which I bought unworking with the electrical problem. I know this is an S80, but the design is extremely similar.

For the XC70 I owned, here is what happened. The headlight blew and rather than leave an open circuit the bulb managed to completely short out. This took out a fuse or two, shunt and/or relay as well as the alternator. I went through a complete and unnecessary CEM rebuild as the relay and/or shunt was the problem. Originally the fuse did not provide the necessary protection - although it is possible it did and the other two parts and alternator were a separate issue (which I doubt as the coincidence is too strong). What I think happened is the bulb went out, blew the fuses and alternator electronics, damaged a shunt and/or relay. As part of this process other unrelated systems were affected, namely the CEM's shunt/relay. When I fixed the headlight fuses I was blowing the CEM fuse. In addition, on the XC70, the failed headlight fuse was under the hood, as well as on the interior side dash panel which was if I recall correctly A CEM fuse. It kept blowing because of the shunt/relay being bad.

The information RickHaleParker provides is the exact methodology I followed to figure out my problem. I will defer to RickHaleParker that a relay is not part of the circuit as I have not examined it closely for your car and it appears he has superior knowledge.

Start with the simple, check the fuses both in car and under the hood (if the S80 has this) and then dig deeper if you do not find the solution. What I mapped out for the XC70 could be similar in a worse case scenario. If the simple fuse check does not work look where I did. You can go to a wrecker and pick up some used shunts and relays for cheap and just swap out the two that are part of affected system.

Post by **RickHaleParker** » 16 Mar 2018, 14:16

You may be correct on the relays

I searched the entire document for a headlight relay ... there is not one on the 2001 S80.

However I'll acknowledge the Volvo EWDs are a little wanky, I been fooled before.

Post by **SuperHerman** » 16 Mar 2018, 14:37

RickHaleParker - I am not saying you are wrong as I don't have access to a 2001 S80 wiring diagram.

But I did find a 1999 Late Model Version wiring diagram on line and for the underhood fuse box I see under "Main fuses, 11B, in the integrated relay/fusebox" that is states No. 1 "Fuses 11C/10-11 (via high beam relay) and No. 2 "Fuses 11C/1-2 (via low beam relay and shunt low beam).

When I did my research I learned that because the electrical demands of the headlight systems every car I read about had a relay involved to handle the electrical load.

I am so out of practice reading the wiring diagrams I am not going to try. What I am saying that when I had a similar chase down with the XC70 the shunt and/or relay was the ultimate issue - and the culprits were on the CEM. In the current case it may just be a fuse - but OP has to check both the underhood and in car fuse boxes as a starting point.

Post by **RickHaleParker** » 16 Mar 2018, 15:43

RickHaleParker - I am not saying you are wrong as I don't have access to a 2001 S80 wiring diagram.

Never suspected you where. My intend was to communicate what some of the information I'm working off of.

I am so out of practice reading the wiring diagrams I am not going to try.

The newfangled ones are not like the well thought out old school EWDs. The newfangled requires one to read up and down the document to decode reference style numbers. The plain text labels are gone from the wiring diagrams. You got to jump back and forth between the wiring diagrams and the component list just to figure out what your looking at. Darn thing reads like they where designed by a MBA rather then an EE.

Nemodown · Post by **Nemodown** » 27 Mar 2018, 21:03

Real similar problem with my 08 s80 after replacing decaying wiring in both headlights. Thought I was going crazy and very close to ripping out my cem. On a last ditch effort I bought a set of the sylvania basic bulbs and installed with the battery disconnected. My low beams are back....

hmsky83 · Post by **hmsky83** » 26 Aug 2021, 20:00

I had the same problem where my passenger side low beam wouldn't work tried replacing the bulb nothing !!! checked fuse 20 and 21 both were good checked to see if there's any voltage at the bulb socket and that's when I found out there is no voltage.

Well the fixed turned out to be fuse number 17 was bad. Replaced it and all is good now. I guess 18 is the driver's side. Hope this helps someone who's a noob like me LoL