This week, one of our customers came in with the heated mirrors on his Dodge Caravan not working. We seized the opportunity to create a post to show you how to diagnose and fix such a thing. Faulty heated mirrors is a pretty common problem everybody should be able to repair, no matter how experienced you are as a mechanic.
First, use a small prybar or screwdriver to gently pry and remove the mirror’s glass. Be extra careful! These things are super easy to break!
You’ll find two small connectors on the back of the glass which are the positive and negative wires powering the mirror’s circuit. Unplug them. The most common cause of non-working heated mirrors is an open circuit. This means that the little wire enclosed in the mirror’s glass is cut somewhere and stop the flow of current, preventing the wire to heat up, thus, no heated mirrors. To test the mirror’s circuit, you need to use a multimeter. If you need help with that, check out this article on how to use a multimeter.
Select the Resistance Testing mode and put the two probes of your multimeter on each contact behind the mirror’s glass. If OL or 0 appears on the screen you know for sure the circuit is busted. You then need to replace the glass itself.
If the circuit is good, something should show up on the screen. It’s hard to say what because it depends on the design, the size, and the material used to create the wire. Here we have an 18.16 Mohms reading telling us the circuit is good. Onto next step.
Now, we need to test the positive and negative of the car’s circuit. For this test, you can also use a test light. Personally, I prefer the multimeter but it’s really up to you. Connect the two ends of your test light or the two probes of the multimeter to the two connectors coming from the car. Start the car and turn on the heated mirrors. If the light doesn’t light up or if the reading is still OL or 0v, the power circuit is open and you need to troubleshoot that. This deserves his whole own post but, let me just say that the most common causes are a blown fuse or a busted switch or relay. I’d check that first. If it’s still not the problem, the wires may be cut somewhere in the harness. If everything is ok the test light should light up or you should read something between 13.7v to 14.7v on the multimeter.
Everything was good on our side. Moving on!
You now know that there are power and ground to the mirror and that the circuit itself is in good working condition. In this situation, there is only one explication left. Bad contact. The power or the ground doesn’t have a good contact with the heated mirror’s circuit because of dirt or corrosion. In that case, use some sandpaper and sand both the connectors and the pins. You can also use a pair of pliers to gently squeeze the connectors to ensure good contact with the pins.
Finally, re-connect and re-install the glass and test that it is now in good working condition. To do that, use an infrared thermometer. Measure the temperature of the glass before and after it’s turned on. Again, there’s no right or wrong answer but you should see the temperature rise. For us, the measurements were 9.5 degrees Celsius before and 24.9 after.
That’s it! Fix confirmed!
I hope it helps!