Diagnosing rear defogger: Accord 2000 LX

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  #1  
Old 12-03-12, 11:12 AM
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Diagnosing rear defogger: Accord 2000 LX

Hi!

Thanks for all the previous advice here for the last 9 years and two cars!

I am trying to diagnose why the rear window defogger does not work in my Honda Accord LX 2000, 4 door, 4cyl, manual. I bought the car 5 years ago, and the defogger never worked. No voltage on the defogger contacts at the window. The light turns on when the switch is pressed, and there is a click in the right-front area (I am guessing - a relay).

How can I diagnose the problem? Is it worth giving ~$100 to the shop to diagnose it (that's what they estimate the check would be, no fixing, and they seem like honest guys)?

What kind of repair this may be, is it even worth starting if it's wiring? Are these wires reasonably accessible without taking the whole car apart?

I am planning a 4K mile family trip, and I figured it won't hurt to try to fix the defogger if I can manage it.

Thanks!
 
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Old 12-03-12, 11:26 AM
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How are you measuring the voltage?
Are you testing with a multi-meter (on DC) between one tab and the car body or between the two tabs?
Generally if the defrost light turns on at the control, the fuse is good and it's somewhere else. If it's not the tabs (one or both disconected), then you are probably looking at the control unit (which has a timer of some sort). I haven't messed around with the defrost system other then repair the tabs (broken wires), so I can't provide any info on the control module.
 
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Old 12-03-12, 12:21 PM
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Hey...hold on before paying money...

Like Mike said....where did you check for voltage and how? Did you also disconnect the wires and check the grid itself for continuity?

They are pretty simple things except for the timer part...but I wonder if that might be in the relay? Hmmm...don't see it even mentioned at Autozone. Probably all part of a control module as mentioned.
 
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Old 12-03-12, 12:37 PM
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I used a simple digital voltmeter to test the voltage: turned on the ignition, and checked between the top (+) tab on the window and the body. (The side tab, which I believe is supposed to be ground, is covered by the upholstery, so I figured it's the same as body.) No voltage at all.

I did not check for continuity since I figured I must get voltage either way. I did not disconnect anything. The top tab appears to be connected, the side - not sure, cannot see but I checked against body anyway.

What do you guys recommend?
 
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Old 12-03-12, 01:43 PM
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I would first look for a connector in the trunk. It should have one end going up to the defogger and the other end going to the front of the car. Test continuity on the up connector using the ohms scale on your meter. Test for voltage on the front connector using the DC scale.

If you have continuity but no voltage, locate the relay in the car and check for voltage in and out of the relay. If no continuity thru the defogger grid,it may have a tiny break in the grid.
 
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Old 12-03-12, 02:35 PM
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To goldstar: what connector in the trunk? the defogger in my car has one contact on top, and ground contacts on both sides. I don't think there's anything in the trunk that is connected with the defogger.

I did check the voltage with ignition on, there is none. I think that this makes a break in the defogger irrelevant: break or not, there must be voltage coming in the defogger. Or did I misunderstand?

Thanks!
 
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Old 12-03-12, 07:04 PM
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Instructions

1 Check the defogger circuit fuse and make sure it is in good condition. If necessary, replace it.
2 Turn the ignition switch on but do not start the engine.


3 Turn the defogger switch on.
4 Open the driverís door and look at the dome light inside your car. The light should barely illuminate. If the light is not dim, go to Step 9.
5 Inspect the defogger grid on the back of the window. Start the engine and turn on the defogger.
6 Wait for a couple of minutes to allow the grid to warm up. Trace the grid with your fingers and feel for warmth along the wire. Take a note when the wire feels cold. Thatís where the defogger grid is broken. You might be able to see the wire gaps.
7 Use a test light if you canít see the broken grid segments. Start at the positive connection of the grid. Clip the test light to a good ground on your vehicle and touch the connections of the grid with the pick of the test light. If the test light comes on, you have found the positive side. Follow the grid wire by touching the line with the test light at small intervals. The point where the test light does not illuminate and the previous point is where the broken part of the grid is located.
8 Repair the broken grid segments.
9 Check the connection at the grid and make sure there is continuity between both sides of the connection with a multimeter.
10 Turn on the ignition switch but do not start the engine. Use a test light to check for voltage at the grid connection. If there is no voltage, check the wire between the grid connection and the relay for continuity.
11 Check the relay for incoming voltage and outgoing voltage to the defogger grid using a test light. If there is incoming voltage but not outgoing voltage, check the relay for proper operation. Most defogger relays use an integrated timer that stays on for approximately 10 minutes. If the relay is not working properly or does not stay on for the time required, replace it.
12 Check for circuit continuity from the wire coming from the fuse panel to the defogger switch and check the switch for continuity using a multimeter. Also, check for continuity at the wire going from the switch to the indicator lamp and to the relay. Make the necessary repairs.
 
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Old 12-04-12, 02:28 PM
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Thanks for the instructions! If I have to go for the wires, how hard it is to get to them?
 
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Old 12-04-12, 06:52 PM
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hate to sound this way, but you about to find out. I own and owned Japanese cars, and every time it's pita. Maybe my hands too big. But your grid wires should be easily accessible from underneath trims, and it's all snapped in place. Rear shelf may need to be removed. I did it on inlaw's Corolla, only had to unsnap pillar C trim from inside, and it was all there.
I honestly think, it's something very simple and likely up there at the grid.
 
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