2005 XC70 Headlamp circuit out
 

I have a 2005 XC70 with 125K miles. My driver's side low beam/daytime running lamp is out and the dash message 'bulb failure low beam' is on. I tried replacing the bulb but it was OK. I measure only 0.7V at the bulb connector. I checked the fuse but that is OK and has 12V on either side of it. I looked for a shunt resistor but couldn't find one under the dash. This is where I have read the CEM (electronic control module)is located, which is supposed to have a shunt resistor, but under the drivers side dash, behind the OBDII plug, there is only a fuse panel.

The bulb is a regular 12V so I presume that another frequently listed culprit, the high voltage ballast, isn't used in this model.

Can an experienced user here advise me on where the shunt resistor/CEM is located? My understanding is that the shunt is a low ohm resistor through which the current to the bulb is run. The CEM then is set up to monitor the voltage and will activate the 'bulb failure low beam' message if the wrong voltage is present.

I have worked as an electronic technician for decades and have also done plenty of car repairs. I am frustrated and humbled that I can't fix this simple problem. Please help!:confused:

Thanks--Martin in California:cool:

did you find the prob? I believe I am experiencing the same issue.

mjstonework, nope not yet. Give it a week or so. Do you have the same year and model (05 XC70)?

Not exact, 2005 xc90 also no sign of a high voltage ballast. I can't recall all the exact details but I've no voltage at the headlamp. At the fuze i have 12.4v. So somewhere in-between is shorting. I checked the harness and its fine as well. It sounds like the CEM is a major possibility but before I do anything I am hoping I here other similar stories. Also I wanted to ask what people thought about CEM repair services or is it a wast of money.

I have a 2005 V70, 140,000 miles and my problem is similar, however my left low-beam works by daylight, and the lamp is inoperative after the sun goes down. I have the same service alert at dusk. Any word on this fix?

Not sure about V70's but on the 2000-2004 v40's the headlamp relay on the CEM is a common failure point. When it occurs you will get proper voltage at lamp when bulb is removed but the minute you plug the bulb back in voltage reads 0v. On that vintage it's is an easy enough job to remove the relay from the CEM and replace.