I have a 2001 V70 with 125k and the headlight relay/chip keeps burning out. The low beams both go out at the same time as a result. I had the relay/chip replaced 3 times now in 1 year. When I replaced the headlight relay/chip today, I noted that the relay/chip housing (not sure if that is the correct term) had signs of burn marks.

Any ideas what is causing this? I am concerned if this keeps up, the relay/chip housing will need to be replaced at a big expense.

Thank you for your help!

 

Is it the relay or the low beam shunt that is going bad? I've read the shunt, which is a low resistance resistor type device, can overheat and also burn the contacts. These contacts (in the CEM) need to be cleaned very well before replacing the shunt to prevent added resistance, which causes the damaging heat.

 

Something in that circuit is drawing excessive current; you need to get a schematic of that circuit and see what all is downstream of that relay. Up thru '99 (that's what my manual goes up to) looks like it's only the headlights.

I would insert an ammeter in there and see what kind of current it's drawing...

 

LR, you mentioned signs of a burn mark and I located a picture that may be due to the same problem as you’re having, see the link below, scroll down past the midpoint to see the pictures. If the burn mark you’re seeing is in the same location of the CEM then it’s an overheated shunt connector. The low beam circuit has a relatively high current draw of about 8-9 amps so a resistive contact or bad shunt would cause a great deal of heat, enough to cause a burn mark and possibly damage the connector.
If this is the problem with your car and whether is was a bad shunt or a resistive connection to begin with I suspect the recurring problem you're having is due to the connector inside the CEM slot being damaged from the heat, either the connector spring tension or plating may have been damaged from the heat. It may be possible to clean the connector well enough (see link below) but if the spring tension or plating is damaged enough it will be difficult to get a good (no resistance) high current connection. I haven’t done this with my 2001 V70 but with other cars I’ve owned I’ve replaced these female end blade type connectors. It’s a matter of finding the tab holding the connector in the slot, inserting something very thin in between the connector slot and outside of the connector to press back the holding tab and working the connector out. You will have to locate a connector of the same type for replacement. I’m mentioning the connector repair in case someone suggests replacing the very expensive CEM, this just isn’t necessary in my opinion.

There is also are relay in the low beam circuit, which plugs into the CEM and this low beam relay is located just above the three thin shaped shunt devices (see picture), it’s the bottom relay of 6 or 7 relays in a row. The relay may need to be removed to see any burn mark since it’s more or a rectangular in shape and may hide a burn mark. From what I can tell the shunt connector or the shunt itself are more likely to be the cause of the problem because the shunt is a resistor that generates some heat even when everything is working correctly and potentially a lot of heat if the shunt or connector become even slightly more resistive. The shunt’s purpose is to monitor a current, voltage change when a bulb burns out and sends out a message, it’s really unfortunate it can also lead to the loss of both low beam headlights.

It’s worth checking the current draw as gdog mentioned but I don’t think you’ll find this problem was caused by an overloaded circuit or a short. Everything in the low beam circuit should be able to handle as much current as the 15A fuse will allow but if there is any resistance in this high current circuit it will cause a lot of heat and possible damage. Do check the low beam fuse for the correct rating, it’s located at the end of the dash.

Picture of burnt CEM shunt connector
http://www.volvoforums.org.uk/showth...?t=9910&page=2

Good information from Tech, headlight wiring diagram, CEM removal, pictures don’t appear available anymore
https://volvoforums.com/forum/showth...t=25721&page=2

Some more information about the low beam shunt
http://www.xenonvalot.com/xenonfixvolvo.html

automotive connector information
http://www.rowand.net/shop/tech/auto...connectors.htm

 

Hello,

I have the same exact burnout on my 2000 S80 and the CEM appears identical to the pictures posted here. I looked at the wire connecting to pin 2 and it appeared exposed more than others - so I had thought this might have been the cause for the burnout. I tried pulling out the wire, thinking it was a typical auto wire connection (my mistake) and the wire came out of the connector. I guess the burn fused the metal with the surrounding plastic. Are these connection points supposed to be removed? Since it doesn't appear like pin 2 is directly connected to the CEM other than through the shunt, does anybody know if the entire CEM needs to be replaced due to a single wire connection melting? Is replacing the CEM something a DIY can do, or does it need to be reprogrammed with VIDA?