tlarimer

iTrader: (3)

I'm having problems trying to figure out why the rear window defroster is not heating up and melting snow off on my 99 Civic LX. I have checked fuse #16 7.5a and replaced the relay in the under dash fuse panel, also checked the #7 30a fuse in the under hood fuse panel. The left and right connections on the window seem tight to me. The light on the switch turns on, the relay clicks, but still it's not heating up enough to touch ice or snow. Is this common and I am asking too much of my rear window defroster?

Former User

You need to check fuses 50 (30A) and 17 (7.5A).

tlarimer

iTrader: (3)

ok, going to go do that right now, be back shortly with results.

tlarimer

iTrader: (3)

Ok, #17 7.5a fuse was fine(but manual says thas for heater/ac relay) and this may sound stupid, but where is fuse #50? Owners manual only shows to #38 or 39 and then list under hood fuse panel starting again at #1.

Thanks for the help.

Former User

It's fuse 17 for 99-00 Civics, and fuse 16 for 96-98 Civics.

Hood fuse 50:

tlarimer

iTrader: (3)

OK, I gotcha, both #16, #17 and #50(#7 underhood fuse panel perowners manual)are all good. In the 99 Owners manual it shows #16 as the rear defroster relay fuse, that's why I questioned it.

Is there any way to check voltage to the connectors on the rear window? That way I can rule out bad grid or fault in wiring.

Former User

It must be a typo in the Owner's manual. These should help:

tlarimer

iTrader: (3)

Thanks Ron, I will test everything tomorrow and post results. Hopefully during testing I can identify problem.

Question about the rear window diagram, which side is that window facing? Is that diagram looking at it from the front or looking at it from the back of the car? That way I know which side is positive terminal and negative terminal.

Former User

I believe the view is from the inside. But don't worry, you won't hurt anything if the meter probes are switched. If reversed, the meter either will read negative voltage or not read anything.

tlarimer

iTrader: (3)

I have different style defrost switch than the one illustrated. Mine does not have a 5 pin connector attached to it, instead it runs through a board and is tied into the complete heat/ac control unit.

Either way, with the ign on. the defrost switch depressed(switch lights up and relay clicks) I still get no voltage readings back to the pos. terminal on the window. I found some sort of switch bolted to the under side of the rear deck that has the defrost wires running though it. I pulled the 2 pin connector with blk/blu and blk wires and checked voltage, Nothing.

So does this lead me back to a faulty switch in the dash? I am at a loss and don't have the proper FSM for the 99-00 year body.

Below is a picture of the style dash switches and second picture is of switch attached to rear deck.

Former User

The top picture verifies that you have a 99-00 style center panel, as expected. If you have a sedan, the bottom picture may show the window antenna coil (see circuit diagram). Correct, the 99-00 defogger switch and timer is integrated into the heater control panel, so the 96-98 switch input test I posted is irrelevant - sorry.

I'll post more electrical tests in a few minutes.

tlarimer

iTrader: (3)

Ok, i just saw that the black box is the window antenna coil and the power for the rear window defroster goes through the coil to power the grid.

And yes this is a sedan.

Former User

Connectors C420 and C501 plug into the rear or front of the dash fuse box (see diagrams below). Unplug both connectors.

1) Ignition key off:
At terminal 5 of C420, you should measure battery voltage to body ground.

2) Ignition key in ON(II), defogger switch on:
At terminal 8 of C501, you should measure battery voltage to body ground.

Post the test results.

tlarimer

iTrader: (3)

Are those pinout diagrams from the face or the back(wire side of connector)? I wont get a chance to check these until tomorrow, after it stops snowing.

Former User

I believe the face is shown, though you can verify by checking whether the correct wire color (see diagrams) corresponds to the terminal you test.

From the manual:



.

tlarimer

iTrader: (3)

Ron,
Thanks for all the help in figuring this out. I feel stupidright now, I had the switch on the voltmeter set wrong.

I have voltage back to the rear window grid. 16.7 volts, but the grid itself is damaged beyond repair, according to the grid test, as I am sitting at 15V at the center of window for all but 2 grid wires, which dont register until I move down to the far right(passenger side and then I get a 15v reading.

So with that, my switch, fuses and relay are all functioning properly. I guess I need to start shopping for a new rear window...

nxl7930

Thanks for such a detailed chain of posts. I was able to use your diagrams to troubleshoot my 99 civic's defogger problem. It turned out in my case, the wire had broken off at the input to the window antenna coil. Thanks for guiding me to the correct repair. You guys probably saved me a few hundred in shop fees.

Danny Sihapanya

I just looked at the antenna coil in my trunk and found out to be a broken wire too!

This angers me because i have no idea how i would go to fix this.

2 year bump ayyyyy