Ambient temperature sensor "LO"

jeffsws · Post by **jeffsws** » 20 Dec 2022, 00:54

Hello.

The outside temperature is displaying "LO" in the dash. Which I believe stands for "lost output." I've tested the thermometer (and two others I have spare) with a multimeter and they work. When it's cold it rises, and warms drops. My guess that the problem is one, or both, of the wires. Is there a way to test them with a multimeter? I would like to test for continuity, but I've no idea where the wire ends, which I assume in a connector under the fuse box. Is there any current sent through them when the key is on? Sorry, but I have no idea how they work. Anyone ever had similar issues?

Thank you for any help.

Post by **jreed** » 20 Dec 2022, 05:18

My dash also reported LO when I disconnected the sensor ('97 855 GLT). I haven't had the situation I think you're describing in which the sensor seems to work and respond when you measure the resistance as a function of temperature.
I haven't looked at the wiring diagram, and that would be the best place to start, but my guess is that there should be a voltage/potential difference between the two wires when the ignition is on. Not sure what the voltage should be... It may be 12V or 5V or some other voltage. You could probe the connector and test for that with the multimeter.

jeffsws · Post by **jeffsws** » 20 Dec 2022, 06:38

Thank you for the reply. I checked voltage and there was nothing. I did manage to test for continuity in both wires. I probed the green connector at the cluster and was able to find both wires. So the wires are not broken at least, so a power issue? Everything else work in the cluster...

I found this pdf
http://www.volvo850.ru/shem/1996.pdf

Page 136 and 144 shows the wiring diagram, but I'm not certain what I'm looking at.

Post by **scot850** » 20 Dec 2022, 13:58

Does your car have the switch you rotate to get fuel consumption info etc, as well as the external temperature? If you do, have you tried to turn it to a different setting and back again? I have had that issue in cold temperatures on my car in the past and that usually gets it running again. Not sure why it does it but only when really cold.

Neil.

jeffsws · Post by **jeffsws** » 21 Dec 2022, 04:36

Yes, I have the rotate switch. No difference when switching between different settings.

I rechecked the wires for voltage and now both have around 5V when the key is on. I was testing incorrectly before and that is why it showed 0. So this tells me the sensor has to be broken, despite all three of the ones I have work fine with the multimeter. At a loss...

Post by **jreed** » 21 Dec 2022, 04:56

Puzzling... if you are reading 5V between the two wires, you could hook up a resistor or two between them to verify that the gauge reads different temperatures. You could also check that the contacts in the connector and the sensor are intact, clean and free of corrosion.