Diagnosing Rear Defog and Heated Mirrors

[3kushn]

After getting my 2021 Limited back from the Body Shop and it getting cold, I noticed my Rear Window Defog and Heated Mirrors aren't working.

Wiper works fine and the LED on the Rear Defog Switch is lit.

First, I can't find a Fuse Diagram that looks like what I have. I'm looking at imgVEHICLE.com but that doesn't look right.

I haven't tested the circuit across the window yet.

Seems to be some relationship between mirrors and window but can't find anything.

Obviously there has to be something like a limit switch controlling the wiper and heater. Could there be something with the switch that allows wipers but no defrost? Possible??

Thanks in advance for your thoughts.

Sorry for the large photo. This is my actual fusebox cover.

 

[97BlackAckCL]

What kind of work was performed at the body shop? Does the rear window roll down?

 

[Saker]

Check MIR HTR fuse

 

[3kushn]

Everything works except no defrost.

The MIR HTR is a relay. I'll check it but wouldn't think that would go out in 3 years.
But stranger things have happened.

Edit
OOPS
Just noticed the 10Amp MTR HTR fuse

 

[3kushn]

Sorry, its been a long time since I started this thread and today I finally had a chance to dig in a little bit.

To make a long story short, I just noticed that on the power switch for mirrors and rear defog that the right side LED doesn't light up. Guessing that's Rear Defog.

Can someone please advise on troubleshooting this issue.

I assume I may need to pull the switch out of the dash. How is that done? Just pop it out with a thin blade?

Edit: I guess I have other questions. Where is the switch that shuts down the rear wiper and rear defog? Is there a switch for each system? I'm wondering if that's a possibility. I'm thinking if the window is down/switch is not charged, the LED on the Rear Defog will not light up??

 

[Humble Leader]

if the rear window is not rolled up all the way the rear defog and wiper / washer will not operate. the light will not illuminate. I doubt the switch in the dash is the issue unless you had your dash apart. more than likely the vehicle thinks the rear window is not all the way up

try this rear window reset procedure. should be the same for 5th gens. it's unlikely the rear wiper/washer AND the rear/mirror defog both stopped working at the same time. I'm betting this is an issue with the vehicle not realizing the window is closed. what work was done in the rear?

Yes, you need to reset the one-touch features on the power windows and moonroof when you disconnect the battery. The windows use less power to close these days (so they're less likely to crush hands or fingers), so they need to "remember" where the closed position is.

To reset the driver's side power window auto-close:
1. Push down and hold the driver’s door power window switch to completely open the window.
2. Pull and hold up the driver’s door power window switch until the window closes. Continue holding the switch for approximately one second until the switch changes from blinking to a constant illumination.
3. Check for proper operation of the “one–touch open/close” by pushing the switch briefly to the “DOWN” and “UP” positions.

To reset the moonroof one-touch operation:
With ignition switch in the “ON” position, do the following:
1. Push and hold the “TILT UP” side of the switch until the moon roof tilts all the way up and then tilts down slightly (approximately 10 mm [0.39 in.] at the rear).
2. Check for proper operation of the “one–touch slide open/close” and “one–touch tilt up/down” functions by pushing the switch briefly to the “SLIDE OPEN” and
“TILT UP” positions.

To reset the rear window operation:
1. Turn ignition switch to the “ON” position.
2. Push the back door power window switch to the “DOWN” side to open the window.
3. Push and hold the back door power window switch to the “UP” side until the window closes. Continue holding it for approximately 1 second.
4. Check for proper operation of the “one-touch open/close” functions by pushing the switch briefly to the “DOWN” and “UP” position.

The compass will also need to be reset if you disconnect the battery. Instructions for that are in the Owners Manual. You need to look at a map of the country to determine which zone you're in, and the instuructions are slightly different for 2003-2006 vs. 2007-2009.

now if your wiper is actually working but not the defog then you probably have a switch/wiring issue. there are a lot of youtube videos on how to access that defog switch, it is not difficult. remove centre console, side radio trim pieces, two bolts and pull out the HVAC controls. you may actually not need to remove centre console but it might make it easier

 

[Marinetaco]

I'm with Humble Leader. Make sure your rear wiper is working or not. If it's not working either, just open and close your rear window. Happens all of the time. Looks closed, but even the slightest bit down will keep it from working.

 

[3kushn]

if the rear window is not rolled up all the way the rear defog and wiper / washer will not operate. the light will not illuminate. I doubt the switch in the dash is the issue unless you had your dash apart. more than likely the vehicle thinks the rear window is not all the way up

try this rear window reset procedure. should be the same for 5th gens. it's unlikely the rear wiper/washer AND the rear/mirror defog both stopped working at the same time. I'm betting this is an issue with the vehicle not realizing the window is closed. what work was done in the rear?



now if your wiper is actually working but not the defog then you probably have a switch/wiring issue. there are a lot of youtube videos on how to access that defog switch, it is not difficult. remove centre console, side radio trim pieces, two bolts and pull out the HVAC controls. you may actually not need to remove centre console but it might make it easier

Wiper works perfectly. Mirror heat works perfectly.
Zero Rear Defog available. Entire rear window sees no heat.

I had the question of what controls (allows/dis-allows) the wiper when the window isn't all the way up. Gotta be a mechanical switch? If so, does that control Defog? And if so, does this switch cut off not only power to the window but power to the switch/LED?

The Window Reset procedure only talks about the window operation, if that somehow went haywire. The instruction doesn't mention resetting where power goes or not.

Tomorrow I'm bringing it to my trusted shop.
Wishing I could jump start their diagnosis.
Seems the switch for Defog isn't getting power, indicated by LED not lit.