2006 XC90 with 141k new to me. Sorting out a few issues and I have hit a brick wall. Starting with what I thought was low hanging fruit, the Bulb Failure Position Light warning message... I discovered that all the position lights (wedge style) front and rear were burned out. Odd for all of them to go bad, chalk it up to poor maintenance from the PO. I replaced the two in each headlight housing and two in the rear bumper lower reflectors. The larger bulbs in the lower inner taillight housing tested out fine so I did not replace. They appear to be the proper style bulb (pegs line up in the socket and they have the dual filament / dual contacts on the bottom). I turned on the position (aka parking lights, aka taillights) and resulted in perfect operation of the front, but the rear will not illuminate. Brake lights, rear turn signals, reverse lights, license plate lights and single rear (driver side) fog light all work perfectly. Cleaned and bent the contacts up on the sockets. Put a test light on it and found no power going to the contacts. Power does flow to the rear fog light contact. Checked every fuse under the hood, under the steering wheel, in the driver side panel, and the cargo compartment. Wiring looks fine. If I bridge the rear fog light contact with the position light contact in the drivers side tail socket, all four rear position lights illuminate so the bulbs and at least that part of the wiring are intact.


Another issue and possible clue, the headlight control switch has a little green LED next to the "parking light" position. That light is constantly illuminated! Is that normal? The position lights that do work do not illuminate unless I turn the headlight switch to the parking light position.


One final clue. I noticed while stopped the the shade of an overpass today, my gauge and dash illumination is always on, regardless of headlight switch position. Perhaps this is also why my HVAC indicator LEDs are hard to see during the day? Also, my DRLs are the same brightness as my normal low beam headlights. The license plate lights are always lit as well (with ignition in the on position or engine running)


I don't want to start throwing parts at the car without knowing what is going on, especially if it's the pricey CEM. The headlight switch assembly seems like a possible culprit. I don't see any relays or shunts to check as I think this was the model year they switched to transistors? Just accessing the CEM to check for water damage and corrosion seems very labor intensive. Thoughts?

 

Daytime running lamps (if turned on in the CEM, off is available in some markets) are the regular low beams and parking lights front and rear -

It's not unusual to find many wedge style bulbs out in that year range xc90- usually I have to replace many during a major service. Maybe because they are on all the time - with VIDA you can turn daytime running lights off - and bulbs will last much longer

Having a hard time understanding what you think your problem is - do the parking lights not work with the light switch in the off (as daytime running lights) or the fully on position?

If you have a bulb out position light warning - the system only cares about the rear parking lights (on your car) - generally the system compares the current used by the left bulbs to the current used by the right side. If different brands or old and new bulbs are mixed that can cause a bulb out warning.

The bulb out system usually only cares about the low beam bulbs, the 3 brake lights and the 4 rear parking lights. Some cars will get turn signal or rear fog bulb out warnings. Some cars (not yours) care about the front parking lights.

Here's a wiring diagram. Note the front parking lights are powered from the CEM, rears powered from the REM (in the trunk). 10/11,71,12,73 are the front parking lights, 10/18, 17 are the rear parking lights. I've seen many times a cem turn off power to a circuit perhaps when a bulb shorts out - (note no individual fuses for left and right parking circuits that older Volvos had) Sometimes that required scanning the car and finding cem (or rem) codes and clearing them to restore power to a circuit. You might try rebooting the car. Touch the battery terminals together for a few seconds (with one disconnected of course) to shut down all the control units. Also note the signal from the light switch module is a network signal (square wave icon above the wire on the diagram) I doubt you have a bad switch. 10/3 is the tag lights

 

Thanks for your reply! I'm used to cars that run the headlights at a lower brightness for DRL, or have a totally separate bulb for DRL. So with headlights in position 0 I can expect to see what on this model? Parking lights? License plate light?

My main problem is cars behind me cannot see me at night because the tail lights (running lights/position lights, so many names) get NO POWER.

The constant dash illumination and parking light led on the headlight control were two related or maybe unrelated things I thought I would mention to help with a diagnosis.

 

REM fuses all OK. Looks like this dangling loose box is the parking sensor ECU (that system works great). Has adhesive on the back. Note the green connector below and to the right with nothing plugged into it.

Top terminal gets 8.9 volts, jumps to 10-11v when rear fog button is pressed. Lower terminal reads zero in all situations. Zero on passenger side as well. License plate lights up fine. Wedge lights inside the reflectors light up when I bridge these two with the rear fog on.

This is the tail light / rear fog light bulb. Put voltage to it and both filaments are working.


Trying the battery computer reset tip today. Will report back if that fixed it.

 

UPDATE: Went to my local independent Volvo service spot and they reset the computers for me (nice guys only charged 15 min of labor). This fixed the problem and all lights work (for now). My parking indicator LED on the LCM still lights up all the time, is this normal for a 2006 xc90? The battery lead touch-together trick did not work and I was told not to try it again due to risk of making problems worse...

 

It does not "make things worse" to disconnect your battery, drain the memory from controls units and restart. It's simply the same thing as replacing the battery. That does work sometimes - I fixed Volvos for 40 years - so take my opinion or not.

I was guessing that you did not have free access to VIDA. I'm glad a scan and erase fixed your problem - that would have been the first thing I would have done using VIDA. Have seen that fix many problems many times.

 

Hah yeah I didn't say I agreed with him! Your suggestion was a great, and free, place to start. Might have to get VIDA now. Do the consumer models allow you to disable DRLs or is that only at the dealer? I like the safety aspect of it but why does Volvo light up the front AND back of the car like a Christmas tree during the day?

 

Vida (or a compatible scan tool) is needed to change the operation of the lights switch. Either the free stolen/hacked 2014d Vida or a subscription will work. Screenshot is the page where it's changed. The rear parking lights are on with DRL - How many cars do you see at night with just their DRL on - with no rear lights? Where I live there's a bunch of people who don't turn their lights on at night! (or in the rain, etc.) Or have their front and rear fog lights on all the time to look cool.

 

Did the problem ever come back? I am having the same issue and resetting the ECUs didn't help. It happens intermittently. Thank you!