How to test side mirror for heat

Post by **m491** » 24 Jan 2013, 16:15

This week I got in my kids 850 on a cold day with frozen water on the side mirrors. I flip the defrosters but only the rear window defrosts. I have replaced a mirror in the past on another 850 in the family but I wasn't sure if there is a way to test to make sure the defrosting element still works. I have a multi-meter but no clue on how to test the mirror to see if it is working correctly. It's a dumb question so I apologize. I hate to spend the money on a new mirror if I have a bad switch or wiring. (Both mirror will not defrost.)

I want to make sure the kids have clear mirrors on these winter day. (Plus I hate when all the things on car don't work.) Thanks folks for the help in advance.

Post by **JDS60R** » 24 Jan 2013, 16:27

Check the mirror heater wires for high resistance across the wires. Then hit the defrost button and check the wires from the car for DC voltage.

If the car is not giving voltage you may have a bad fuse or break in the wire.

If there is "no" resistance (same as probes not touching each other) in the mirror then the circuit is broken and you will need to replace.

Post by **regent** » 24 Jan 2013, 16:38

if both mirrors are cold look at the fuses first

Post by **m491** » 24 Jan 2013, 17:37

I am not experienced with the volt meter besides checks on my battery. How do you check the leads on the mirror with the meter?

Post by **regent** » 25 Jan 2013, 19:21

With a cheap meter that has at least Voltage and Resistance Modes, you can do the following (to check what JDS60R recommended earlier):
1. Resistance check:
--Power OFF
--Meter switched to Resistance Mode
--Connect meter probes to heater terminals to read resistance. The value you want to see is just a few ohms. If you see high resistance (like several kOhms or MOhms), then the heater has failed open. Simple to fix: Replace.

2. Voltage check:
--Meter switched to Voltage Mode
--Connect probes to heater leads
--Turn defroster ON
--Read voltage (power supply to heater) - you want to see something close to battery voltage (like 11 - 12 volts). If you read less than 90% of the battery voltage, the problem is in the circuitry outside the heater (poor contacts, etc.) If you see zero volts - then there is an open outside the heater. You will need your car's electrical diagram to trace the fault. Fix may be easy - like a bad fuse, or relay contact (or more complicated if there is a pinched wire or a recessed connector pin).

luckykolo · Post by **luckykolo** » 25 Aug 2020, 16:13

Anyone has actually measured the voltage at the warming pad on the mirrors? Is it 12V? Thanks

luckykolo · Post by **luckykolo** » 25 Aug 2020, 18:27

luckykolo wrote: ↑25 Aug 2020, 16:13 Anyone has actually measured the voltage at the warming pad on the mirrors? Is it 12V? Thanks

Btw here is nice video about mirror disassembly process

Post by **BEJinFbk** » 26 Aug 2020, 01:17

luckykolo wrote: ↑25 Aug 2020, 16:13 Anyone has actually measured the voltage at the warming pad on the mirrors? Is it 12V? Thanks

Yes - 12 volts.