Rear View Mirror Temp and Compass Not Working (3 Simple Fixes)

Imagine heading out for a drive and your temp/compass isn’t working. You don’t even have to imagine it because it’s exactly what happened to you! So frustrating, right?

So, why are your rear view mirror temp and compass not working?

The PCB of the mirror is to blame. It is because of the fractured solder joint in one or more of the resistors due to overheating. To solve this problem, you have to disjoin the resistors from the board and re-solder them properly.

Not yet clear about the whole process? Stop worrying, hang on tight with us and let’s figure out the details! Here we’ve explained everything step by step for you.

Why Is Rear View Mirror Temp and Compass Not Working?

Before jumping into fixing it, let’s understand first what’s even causing this problem!

The temperature and direction are shown in a vacuum fluorescent display (VFD). You can see the VFD when you open the mirror. Whenever it is an issue with the VFD, it is usually in the hot wire circuit. This case is no different.

The hot wire circuits are drawing current constantly. So, the resistors often get heated up and start thinning out. At some point, they crack because of the excessive heat and your temp/mirror goes out.

Because of that, you don’t know in which direction you’re driving. You can’t even read the temperature outside. You may have to get your phone out of your pocket for these which is not safe while driving.

How to Fix Rear View Mirror Temp And Compass Not Working?

Though it’s a major problem, fixing it can be quite easy. We just have to get to the circuit board and resolder the resistors carefully. It would not be very much trouble if you know how to solder.

Tools Required

Pry bar
Solder sucker

Flux
Soldering iron

Now we have everything we need. So, what are we waiting for? Let’s get started!

Step 1 of 3: Open The Cover

First of all, you need to remove the rearview mirror. Then open the cover of the mirror using a pry bar or other prying utensils.

Put the tip of your pry bar inside the cover joint. Once it’s in, run it along the joint and you’ll pop it open. This could be the most time-consuming step in the whole process!

Step 2 of 3- Take Out The Resistors

Once the cover is opened, you can see the circuit board. It’s connected with the backside of the cover with a connector. Take it out and it’ll leave the circuit board alone.

On the upper and lower edge of the VFD, you can see the edges of a few lines of wires. They are the hot wires.

Now flip the board around. You’ll see 3 tiny black things that are labeled “4R3”. These are our culprits here, the resistors.

Look very closely at the resistors. Here, you’ll see that at least one of the resistors has a crack on its solder joint. Now you can take your tweezers and slightly push the resistors to see if they fall off easily.

If not, then take your soldering iron and reheat the solder joints of the resistors. Keep your solder sucker near. When the joints are melted, use the solder sucker to suck in the residual solder.

Step 3 of 3- Re-solder the Resistors

The solder requires to make a good bond with the resistors in order to last long. But the metal part of the resistor that we’ll be soldering might create an oxide layer on it.

Every metal creates oxide in the presence of oxygen. It could get in the way of smooth soldering. Therefore, the whole issue might happen again if the soldering is not appropriate.

To get rid of the oxide, we’ll use some flux. If you don’t know which flux would be a good choice, here are our top picks for you:

Now that you have your flux, apply it to the area that we’ll be soldering. Take some solder and your soldering iron and solder the resistor with the board.

Let the solder dry for some time. After it’s dried, it’s time to put everything back on. Connect the circuit board to the cover using the connectors. Finally, install the mirror in your car, and voila! You’re done.

Precautions To Take When Soldering

There are not many difficult tasks during the process. But soldering can be quite troublesome as the components we’re dealing with are very small. So, make sure that you’re following these precautions-

Don’t touch the solder until it’s completely cooled down.
Solder carefully so it never touches other areas of the PCB.

Don’t keep any water where you’re working.

Maintaining them will help you avoid any unwanted troubles.

Frequently Asked Questions

Q: How can I reset the temperature on my rear view mirror?

Ans: Press and hold the “Temp” button on your rear view mirror until it turns itself off. It takes around 6-8 seconds based on the car model. And then press and hold it again. Your temperature is reset!

Q: How to calibrate rear view mirror compass?

Ans: Drive slowly in a circle until the mirror shows a direction. It means that the calibration is complete. Then drive in a circle 2-3 more times to fine-tune it.

Q: What does the power button do in a rear view mirror?

Ans: It is the auto-dimming button. When it’s turned on, it helps to reduce the headlight glare.

Final Words

We hope you’ve fixed your rear view mirror temp and compass not working.

But if you’re not confident enough with soldering, you should not do this by yourself. It may cost you more than you would’ve saved. Rather get it done by someone experienced or by a professional.

Happy driving!

Author

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Rob Dahm

My name is Rob Dham. I am the founder & managing editor of greaseandgears.com. I am trying to offer invaluable insights and solutions to everyday vehicle-related challenges.