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Discussion Starter #1
Dear All,

I have an issue with my rear windshield defogger. I looked at a couple of previous threads including the one shown below,

http://www.subaruoutback.org/forums/80-electrical-electronics/51198-2005-outback-rear-window-defogger-not-working.html

Based on the above, and few other threads and FSM I did the following diagnosis.

1. Checked fused M/B 10 and F/B 22 (A/C fuse) and they are both good.
2. Defogger switch seems to be working fine as the yellow light comes when both fuses are in (not when one of them is out.)
3. Continuity between left and right terminals is rear defogger grid is good.
4. No voltage across the same two terminals when defogger is turned on.
5. Checked the wiring at all 4 boots at the rear hatch. They seem to be fine with wires inside the insulation except on right lower boot where wires are exposed, but, no visible damage.

based on the above should I replace the relay or should I rep the rubber wiring case apart and check for broken wires?

Thanks
 

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Discussion Starter #2
Dear All,

FSM says,

__________________________________________________________
Monitor.
(1) Prepare the Subaru Select Monitor kit. <Ref.
to GW-7, PREPARATION TOOL, General De-
scription.>
(2) Turn the ignition switch to ON (engine OFF),
and start “PC application help for Subaru Select
Monitor”.
(3) On the «System Selection Menu» display
screen, select the {Integ. Unit mode}.
(4) Select the {Current Data Display & Save}.
(5) Display the data of rear window defogger
switch.
2) After rear defogger switch is set to ON, check
whether it turns to OFF in 15 minutes or repeats 15
minutes operation and 2 minutes stop?
3) When it becomes OFF on above 2), it is normal.
When it repeats 15 minutes operation and 2 min-
utes stop, replace body integrated unit.
________________________________________________________

I wonder if this procedure can be performed using FreeSSM.

Thanks
 

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2. Defogger switch seems to be working fine as the yellow light comes when both fuses are in (not when one of them is out.) . . .should I replace the relay. . .
If the light does not come on with either fuse removed, then the light is powered from the switched circuit providing power to the rear defogger; i.e., the light indicates when the wire going to the defogger itself has power. That being the case, the relay would appear to be working.

To double check the defogger relay operation, see if the outside mirror heaters warm up when the defogger switch is On. The mirror heater relay is powered from the switched power of the defogger relay. In other words, there has to be power going from the defogger relay down the wire toward the rear window for the mirror heaters to work. If the mirror heaters work, then the defogger relay is fine. (An infra-red thermometer is ideal for checking if the heaters are warming up -- the temperature of the mirror will start to go up fairly soon after the defogger switch is turned on, so there's no need to wait until the mirror is actually warm to the touch.)

3. Continuity between left and right terminals is rear defogger grid is good.
What do you actually measure (Ohms) between the two terminals and is this with the wires connected or disconnected? Unless the wire terminals at the defogger grid are disconnected (or broken), measuring between the terminals could be misleading because (as noted above) the heated mirror relay energizing coil (for the outside mirrors) is across the same points.

No voltage across the same two terminals when defogger is turned on. . . .should I rep the rubber wiring case apart and check for broken wires?
A broken wire there would seem to be a good possibility. Are all the other electrical functions in the rear gate working properly (e.g., rear wiper, --
including intermittent operation, and parks at the horizontal position --, back-up lights, hi-mount brake light, lock/unlock latch, and cargo area ceiling light works when hatch is open)?
 

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Discussion Starter #4
If the light does not come on with either fuse removed, then the light is powered from the switched circuit providing power to the rear defogger; i.e., the light indicates when the wire going to the defogger itself has power. That being the case, the relay would appear to be working.

To double check the defogger relay operation, see if the outside mirror heaters warm up when the defogger switch is On. The mirror heater relay is powered from the switched power of the defogger relay. In other words, there has to be power going from the defogger relay down the wire toward the rear window for the mirror heaters to work. If the mirror heaters work, then the defogger relay is fine. (An infra-red thermometer is ideal for checking if the heaters are warming up -- the temperature of the mirror will start to go up fairly soon after the defogger switch is turned on, so there's no need to wait until the mirror is actually warm to the touch.)
Plain OM, I do not have mirror heaters. My 08 Outback is the base model. I will check the rear defogger with a infra-red thermometer.

What do you actually measure (Ohms) between the two terminals and is this with the wires connected or disconnected? Unless the wire terminals at the defogger grid are disconnected (or broken), measuring between the terminals could be misleading because (as noted above) the heated mirror relay energizing coil (for the outside mirrors) is across the same points.
You are absolutely correct as there are parallel circuits. I am a bit concerned on this as well as I am not sure the DC resistance that I measure between the left and right terminals of the defogger is the actual resistance. Can I remove one of the wire terminals without damaging the connector? If so, what is the best method to disconnect one of the terminals?

A broken wire there would seem to be a good possibility. Are all the other electrical functions in the rear gate working properly (e.g., rear wiper, --
including intermittent operation, and parks at the horizontal position --, back-up lights, hi-mount brake light, lock/unlock latch, and cargo area ceiling light works when hatch is open)?
Rear wiper works properly with all features and parks properly with the hatch open. All the other lights work when the hatch is open as well. Therefore, I will see if there are broken wires. I do not see any right now at all 4 boot ends though.

Thank you for your advise.
 

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Plain OM, I do not have mirror heaters. My 08 Outback is the base model. I will check the rear defogger with a infra-red thermometer.

You are absolutely correct as there are parallel circuits. I am a bit concerned on this as well as I am not sure the DC resistance that I measure between the left and right terminals of the defogger is the actual resistance. Can I remove one of the wire terminals without damaging the connector? If so, what is the best method to disconnect one of the terminals?
Removing the wires from the terminals on the glass can be problematic. There's been cases of the terminal being pulled off. It's soldered to the grid on the glass. Doing that in a factory setting is okay, but it's very difficult to repair in the field. If the wires have not been removed, then I'd suggest not trying. I was only asking to get a better idea of how your continuity measurement was made. But that said, what resistance (Ohms) did you find between the terminals?

Rear wiper works properly with all features and parks properly with the hatch open. All the other lights work when the hatch is open as well. Therefore, I will see if there are broken wires. I do not see any right now at all 4 boot ends though. . . .
Sometimes the break is in a wire toward the center of the round bundle of wires, and isn't apparent. The 12 V to the defogger should be a red wire with a blue stripe (or dots). The other side of the defogger is the ground, which is a black wire, but that wire is also the ground for the wiper motor, so if they work, then the black wire is probably okay. If you can find the red wire with blue stripe at either end of the rubber boot, hold one end and pull on the other end. If the wire is broken through, it might pull out of the bundle.
 

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Discussion Starter #6
Removing the wires from the terminals on the glass can be problematic. There's been cases of the terminal being pulled off. It's soldered to the grid on the glass. Doing that in a factory setting is okay, but it's very difficult to repair in the field. If the wires have not been removed, then I'd suggest not trying. I was only asking to get a better idea of how your continuity measurement was made. But that said, what resistance (Ohms) did you find between the terminals?
The DC resistance between the left and right terminals in the grid that I measured is rather low at 2.6 ohms. Can it be this low? Does this mean that there is a short circuit somewhere?

Sometimes the break is in a wire toward the center of the round bundle of wires, and isn't apparent. The 12 V to the defogger should be a red wire with a blue stripe (or dots). The other side of the defogger is the ground, which is a black wire, but that wire is also the ground for the wiper motor, so if they work, then the black wire is probably okay. If you can find the red wire with blue stripe at either end of the rubber boot, hold one end and pull on the other end. If the wire is broken through, it might pull out of the bundle.
Let me look at all the wires in the bundle again and report back.

Thank you for all your help.
 

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Not to step on @plain OM's toes since he's the one who's been working with you here...

Ohm's Law says 2.6 Ohms across 13 Volts will allow a current of 5 Amperes (I = E / R; current = voltage / resistance). 5 Amps times 13 Volts is 65 Watts (P = I E; power = current times voltage). As a swag, this does not look unreasonable.

Carry on!

[Edit] Yo! @priyadar
 

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Discussion Starter #8
Not to step on @plain OM's toes since he's the one who's been working with you here...

Ohm's Law says 2.6 Ohms across 13 Volts will allow a current of 5 Amperes (I = E / R; current = voltage / resistance). 5 Amps times 13 Volts is 65 Watts (P = I E; power = current times voltage). As a swag, this does not look unreasonable.

Carry on!

[Edit] Yo! @priyadar
Thanks. Next step would be to open the plastic panel behind the bottom of the hatch to trace the two terminal ends and find our if they get power. At the same time, I will try to locate the red wire with blue stripes. In the attached image, I do see a red wire with gray stripes and I wonder if it is the same wire feeding power to the rear defogger.
 

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Thanks. Next step would be to open the plastic panel behind the bottom of the hatch to trace the two terminal ends and find our if they get power. At the same time, I will try to locate the red wire with blue stripes. In the attached image, I do see a red wire with gray stripes and I wonder if it is the same wire feeding power to the rear defogger.
No need to check for power at the terminal ends, unless you suspect one of the terminals isn't attached to the grid.

Your photo shows a red/blue wire. That's going to be the defogger power wire (as far as I know, colors are not repeated in this bundle). That's the same color combination as in the photo in the reference thread you linked to in post #1. (see attached)

I believe there's another way to confirm if the wire to the defogger grid is broken.

With the ignition Off, measure the resistance from the grid to a good ground in the cargo area. If the ground is good, it will be either the resistance of the grid (your 2.6 Ohms) or less. If it's bad, the measurement will be very high/open circuit.

If the ground checks out good, move to the engine compartment.

Measure the resistance from Fuse #10 (in the engine compartment fuse box) to ground (battery negative post is nearby). If the power wire to the grid is intact, then this measurement should be fairly low, i.e., the resistance of the grid plus the wiring to it. If the grid measured 2.6 Ohms, the measurement between the fuse and ground would probably be no more than 4 Ohms. If the measurement is very high/open circuit, then the red/blue power supply wire to the defogger grid is broken.

The fuse need not be removed for this last test. The fuses have small openings in the top above the blade contacts. This opening allow a test probe to make contact with the top of the blade.

@skipw All helpful input is appreciated.

Incidentally, I measured the resistance across the defogger grid on my 07. It was about 1 Ohm. I also measured from fuse #10 to ground, and it was only a tenth or two more Ohms. This would put the current somewhat higher. But it's only for reference; your conclusion that the grid was good stands.
 

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Quick bump since I just started encountering this issue. Up here in VT it has been in subzero temps and I would really like my defogger to work.

Rear defogger light comes on, then turns off after ~15 minutes.
Checked the fuses - the 25a in the engine bay and the 20a in the cabin box. Both great, swapped them anyway.
Examined the wire bundles in the back they look fine, I didnt pull them out but will if I need to.

My one issue is that I just had the free airbag recall done at my local subaru dealer (they also did the brake lines!), when I got the car back, the heater, seat heater, etc. were not getting power to them, so I drove back to the dealer to drop my car off again. They reconnected the wiring, all is well.

Could there have been a different wire, that was NOT properly reconnected? Like I mentioned the defogger light comes on and off as it should, just not working in the back window.

Thoughts?
 

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@treevis

If the light in the switch comes on initially, and goes off after 15 minutes, that's normal and it confirms the control relay and the fuses are functioning properly.

Could there be another wire that wasn't connected? Looking at the wiring diagram (see attached), I'm inclined to say no, given that the switch light/indicator does work properly. There doesn't appear to be any connectors in the wiring under the dash that would have been removed, and not reconnected, that would allow the switch and timer to work (and the switch light) but not the grid at the back.

The problem would more likely be in the wiring going to the rear defogger or the defogger grid itself. As noted above, a very common problem in the 2005-9 is broken wires between the car body and the rear gate (hatch). I'd check that first. If you are comfortable working on the car and have a digital multimeter, perhaps try the test I suggested in post #9 above beginning "I believe there's another way to confirm if the wire to the defogger grid is broken.". That might confirm if the wiring to and through the grid is good.

Have you checked the other functions in the hatch, e.g, do the back-up lights and the high-mounted stop light work? Does the hatch latch assembly lock and unlock, and does the :Door Open" warning light in the cluster show the hatch open, when it is? Also, does the rear wiper work, and does it always park in the horizontal position when turned off?
 

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@treevis

If the light in the switch comes on initially, and goes off after 15 minutes, that's normal and it confirms the control relay and the fuses are functioning properly.

Could there be another wire that wasn't connected? Looking at the wiring diagram (see attached), I'm inclined to say no, given that the switch light/indicator does work properly. There doesn't appear to be any connectors in the wiring under the dash that would have been removed, and not reconnected, that would allow the switch and timer to work (and the switch light) but not the grid at the back.

The problem would more likely be in the wiring going to the rear defogger or the defogger grid itself. As noted above, a very common problem in the 2005-9 is broken wires between the car body and the rear gate (hatch). I'd check that first. If you are comfortable working on the car and have a digital multimeter, perhaps try the test I suggested in post #9 above beginning "I believe there's another way to confirm if the wire to the defogger grid is broken.". That might confirm if the wiring to and through the grid is good.

Have you checked the other functions in the hatch, e.g, do the back-up lights and the high-mounted stop light work? Does the hatch latch assembly lock and unlock, and does the :Door Open" warning light in the cluster show the hatch open, when it is? Also, does the rear wiper work, and does it always park in the horizontal position when turned off?
Thanks plain.

Yes, all things in the rear hatch work just fine, except the stupid defogger. I have not checked the warning light for open hatch though, doing that now—since all lights, wiper, washer fluid and everything seems to be in working order, I was really annoyed since this coincidently came about right after the airbag recall repair.

Ill pull the wires out and see.
 

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Well. Rear hatch alert works on the dash. Pulled the plugs out and wires all look great—both in the hatch and inside when i pulled the siding off to look.

Stumped. Guess Ill have to try and run the voltage
 

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If it were me, I would start with the KNOWN problems. Go back and double check the hatch wiring harness. Just because the insulation is not broken, does not mean the wires are not.

Almost every time this problem comes up, it's the hatch wiring harness causing the problem.
 

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Indeed. Even if the other functions work, it doesn't mean that the defogger wire is good. But if other functions had faults, it would support the idea that the wires are faulty, all the more so the defogger.

The resistance measurement at the fuse that I suggested earlier would confirm whether or not the connection from the fuse to and through the defogger grid to ground is good. If that test shows a high resistance where there shouldn't be one, then that further suggests a problem in the connection somewhere.

Also, it's quite possible that the grid itself is bad. The small traces can be scratched, e.g. while cleaning, and that would prevent the grid from working. Or, the tab on the glass that the wires connect to could come off -- these are hidden under the side trim of the window.
 

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Discussion Starter #16
Plain OM,

Thank you for your help and sorry that I did not have much time to perform the diagnosis until today.

No need to check for power at the terminal ends, unless you suspect one of the terminals isn't attached to the grid.


I believe there's another way to confirm if the wire to the defogger grid is broken.

With the ignition Off, measure the resistance from the grid to a good ground in the cargo area. If the ground is good, it will be either the resistance of the grid (your 2.6 Ohms) or less. If it's bad, the measurement will be very high/open circuit.
I performed this test. Checked the resistance between each end and the child seat latch hook in the trunk head lining. The resistance was 2.8 ohms and 3.6 ohms respectively between the each terminal and the latch hook. Now, that means my blue striped red defogger wire is good in the hatch door wiring cable boot area, isn't it?

If the ground checks out good, move to the engine compartment.

Measure the resistance from Fuse #10 (in the engine compartment fuse box) to ground (battery negative post is nearby). If the power wire to the grid is intact, then this measurement should be fairly low, i.e., the resistance of the grid plus the wiring to it. If the grid measured 2.6 Ohms, the measurement between the fuse and ground would probably be no more than 4 Ohms. If the measurement is very high/open circuit, then the red/blue power supply wire to the defogger grid is broken.

The fuse need not be removed for this last test. The fuses have small openings in the top above the blade contacts. This opening allow a test probe to make contact with the top of the blade.
I performed this test with and without fuse # 10 removed. Each time, I got infinite resistance. This means that I have discontinuity in the engine compartment and in the firewall area, haven't I? Where should I look and concentrate now?

Thanks
 

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. . . Checked the resistance between each end and the child seat latch hook in the trunk head lining. The resistance was 2.8 ohms and 3.6 ohms respectively between the each terminal and the latch hook. Now, that means my blue striped red defogger wire is good in the hatch door wiring cable boot area, isn't it?
No. Those measurements only check the ground connection for the grid.

I performed this test with and without fuse # 10 removed. Each time, I got infinite resistance. This means that I have discontinuity in the engine compartment and in the firewall area, haven't I? Where should I look and concentrate now? . .
This confirms that there is a discontinuity in the red with blue stripe wire somewhere between the fuse and the defogger grid. The wiring in the flexible boot remains the prime suspect until proven otherwise.

Perhaps the next steps might be to first pull the vertical trim pieces at the rear window, in order to verify that the terminals at each the ends of the grid are intact. Then, perhaps find the pair of connectors R37 and D33 (see the wiring diagram attached in post #11 above). This might require removing the right side inner panel of the cargo area below the D pillar. Disconnect the connectors, and then check the continuity from D33 pin 1 to the grid. This tests the wiring through the flexible boot.
 

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Discussion Starter #18
No. Those measurements only check the ground connection for the grid.



This confirms that there is a discontinuity in the red with blue stripe wire somewhere between the fuse and the defogger grid. The wiring in the flexible boot remains the prime suspect until proven otherwise.

Perhaps the next steps might be to first pull the vertical trim pieces at the rear window, in order to verify that the terminals at each the ends of the grid are intact. Then, perhaps find the pair of connectors R37 and D33 (see the wiring diagram attached in post #11 above). This might require removing the right side inner panel of the cargo area below the D pillar. Disconnect the connectors, and then check the continuity from D33 pin 1 to the grid. This tests the wiring through the flexible boot.
Plain OM,

You were absolutely correct. After removing a few trim panels in the hatch, I opened the flexible boot with a great difficulty and found the culprit. Red and gray wire was broken further inside. All the wires were fine without even a single scratch on plastic. So, I soldered the wire and everything is working fine as I tested the defogger last night. Thanks a lot for all your help.
 
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