Rearveiw Mirror Thermometer And Compass Malfunction

wishybone2 · March 23, 2009

Hi! I have a 2004 GMC Sierra 1500 Crew Cab with with the auto-dimming interior rearveiw mirror and compass/thermometer. Sometimes it just goes crazy! Blinking and resetting like 2 times a sec. This can be very annoying if driving at night. Could you tell me where to look to try to fix this loose conection of some kind? I have experimented with certain wires but nothing seems to effect it. It will happen one day and then Also I seem to notice it more when it is snowing. Thanks in advance.

- Ryan

bill190 · March 23, 2009

What I would do if I had that problem is to try to isolate it.

Intermittent problems are difficult to track down, because when you go to test it, everything is working!

The following is a lot of work, but this will find the exact location of the problem...

The suspects would be the mirror itself, power to the mirror, and a wire run to an outside temperature sensor (if it has that).

I would start by looking at the truck wiring diagram and see which wires connect to the mirror power. +12 volts and ground. Then I would get a 12 volt battery or maybe a cigarette lighter plug with a wire in it to supply 12 volts. Then I would disconnect the connection to the mirror and power it from the battery or the lighter plug. I would supply jumper wires using alligator clips or whatever to keep the outside temperature sensor connected. (As well as anything else like a microphone or what not.)

Might want to install some sort of monitoring light if using the cigarette lighter because that circuit could have the same problem! This would verify that power was present if the mirror started blinking.

Then I would drive around like this for a week or however long it takes for the problem to crop up. If the problem disappears, the problem is with the power wire to the mirror somewhere.

If not, then I would look in the wiring diagram for the temperature sensor and see what its resistance is. Then disconnect that wire as well and attach a resistor in its place (outside temperature would always read the same). Then drive around for a week or whatever again and see if that gets the problem to disappear.

If the problem is still occurring, the we would have all the wires bypassed, so the problem would be with the mirror.

Otherwise this would tell you which wires (+12, ground, or temperature sensor) are causing the problem.

If a wire is causing the problem, then I would look at the wiring diagram for connectors for these, then perhaps monitor those with wires strung to various points.

I.e. Wire goes from point A, to connector B, then to connector C, then to connector D and then to mirror. Connect monitoring wires to various points along this path to monitor what is going on. So you know the wire has a problem at point D. Next move the monitoring wires to point C and see what happens when driving around. Then point B. Eventually you will narrow it down to the exact location.

bossier62guy · March 24, 2009

Hi! I have a 2004 GMC Sierra 1500 Crew Cab with with the auto-dimming interior rearveiw mirror and compass/thermometer. Sometimes it just goes crazy! Blinking and resetting like 2 times a sec. This can be very annoying if driving at night. Could you tell me where to look to try to fix this loose conection of some kind? I have experimented with certain wires but nothing seems to effect it. It will happen one day and then Also I seem to notice it more when it is snowing. Thanks in advance.

- Ryan

Pull the connector off of the back of the mirror and check the pins to make sure they're all still locked in place. If they are and reinstalling the connector doesn't do the trick I'd say your mirror is heading south.

wishybone2 · March 24, 2009

Thanks for your help guys! I hope its a wire or pin that is loose cause Im sure that mirror isn't cheap!

- Ryan

Stevens03 · March 24, 2009

It isn't all that expensive, and I'm sure you could find one in a salvage yard even cheaper. I think I've priced them out at about $100 for everything. I was going to install one in a car I had...

Steven