**RE-FIXED with Videos** Rear wiper won't turn off

jlglr4

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It is unlikely that both relays failed, but they are easy to check. Basically, two parallel prongs should have some resistance between, and the other set should be completely open (no conductivity). Apply 12v to the prongs that have some resistance, and you should hear a ”click”. There are lots of youtube videos explaining.

According to the circuit diagram, I think there should be power to the power line of the receptacle even with the engine off. But there should not be voltage to the signal side of the receptacle that turns on the relay.

So, I think the next thing to check is for voltage at the signal wire that turns on the relay (line “J” in the posted diagram). You can tell which side of that receptacle is for the wiper since the wiper turns on when you plug in the relay (the other side is for something else). On the wiper side of the receptacle, there should be a grey-and-purple wire. According to the circuit diagram, that’s the wire that delivers a signal to open the relay. Check for voltage at this wire.

If you see voltage here when the car is off/wiper is off, it is likely a short-to-power issue somewhere between the BCM and the receptacle because the BCM itself should be off and not supplying power (at least that’s my understanding - we can’t normally turn the rear wiper on without the igntion, right?). So, if there is power at the signal line of the receptacle, I think it must be shorting someplace with another power carrying line - perhaps the line that carries power to the power side of that same receptacle. Could also be a problem in the BCM.

If there is no power at the signal wire, then I think we’re looking at a bad relay. Check it out and report back - happy to brainstorm some more on it at that point.
 

Tbh1981

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It is unlikely that both relays failed, but they are easy to check. Basically, two parallel prongs should have some resistance between, and the other set should be completely open (no conductivity). Apply 12v to the prongs that have some resistance, and you should hear a ”click”. There are lots of youtube videos explaining.

According to the circuit diagram, I think there should be power to the power line of the receptacle even with the engine off. But there should not be voltage to the signal side of the receptacle that turns on the relay.

So, I think the next thing to check is for voltage at the signal wire that turns on the relay (line “J” in the posted diagram). You can tell which side of that receptacle is for the wiper since the wiper turns on when you plug in the relay (the other side is for something else). On the wiper side of the receptacle, there should be a grey-and-purple wire. According to the circuit diagram, that’s the wire that delivers a signal to open the relay. Check for voltage at this wire.

If you see voltage here when the car is off/wiper is off, it is likely a short-to-power issue somewhere between the BCM and the receptacle because the BCM itself should be off and not supplying power (at least that’s my understanding - we can’t normally turn the rear wiper on without the igntion, right?). So, if there is power at the signal line of the receptacle, I think it must be shorting someplace with another power carrying line - perhaps the line that carries power to the power side of that same receptacle. Could also be a problem in the BCM.

If there is no power at the signal wire, then I think we’re looking at a bad relay. Check it out and report back - happy to brainstorm some more on it at that point.
OK- I had both relays checked and they are good, according to the guy at canadian tire. I'm going to double-check myself to hear them click or not.

I'll check the receptacle for voltage as you recommend. There is the possibility of a short maybe behind my lower fuse panel, since I did move it quite a bit. It just surprises me that, if I messed up the back of the fuse panel somehow, that the only problem is the rear wiper. I would guess that messing up the panel connections would cause many problems to present themselves.

Thank you, as always, for your clear headed advice.
 

Tbh1981

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Confirmed power to the supply wire at the relay housing. Video link

Maybe it's a BCM programming error due to the battery being disconnected so long? If its a short behind the fuse panel, I'll likely never fix it. There's no way I'm tearing out my entire dash just to fix the rear wiper.
 

jlglr4

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The signal wire terminates at the backside of the central junction box, so either the sunroof drain leak or messing with the connections is the most likely source of the issue. I’m attaching a diagram showing the connections to the junction box. Your connector of concern is C0586L and the pin should be pin 27 (numbered right to left (not left to right) 1-16 on the top row, 17-32 across the bottom row.

Did you inspect the box for water? Is it possible a drop of water got inside one of receptacles? Not sure how wet that area got. If the plug got wet, that‘s all it takes - there is likely a power supply wire to that multi-pin receptacle, and a little water can bridge the two wires. You could pull it back out and inspect it. If there is any water in any part of that assembly, you should get it dried out as much as possible. Water leaks in that area have been known to cause a host of issues months after the fact - I suspect as corrosion builds up.

Not sure how far you can pull it out while having everything connected except that one connector. If you can just remove the one connector and can get to the backside of the CJB, you could probe the pin on the CJB to see if your getting voltage. That would rule out a short to power somewhere else between the CJB and the rear tailgate area.

I doubt its a programming error, but I guess anything is possible.
 

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Tbh1981

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You're very likely correct. The area behind the CJB didn't feel wet, but the drain exits directly above that connector, so I imagine water got on it at some point. Based on my time in the passenger footwell over the last couple days, I know I won't be able to see the back of the box without removing it entirely, and then, I doubt I'd be able to plug the connectors back into their places. I'll give it a good look tomorrow, and if I'm feeling brave, I might try to remove ithe CJB and inspect the connectors in the back.
 

Tbh1981

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The signal wire terminates at the backside of the central junction box, so either the sunroof drain leak or messing with the connections is the most likely source of the issue. I’m attaching a diagram showing the connections to the junction box. Your connector of concern is C0586L and the pin should be pin 27 (numbered right to left (not left to right) 1-16 on the top row, 17-32 across the bottom row.

Did you inspect the box for water? Is it possible a drop of water got inside one of receptacles? Not sure how wet that area got. If the plug got wet, that‘s all it takes - there is likely a power supply wire to that multi-pin receptacle, and a little water can bridge the two wires. You could pull it back out and inspect it. If there is any water in any part of that assembly, you should get it dried out as much as possible. Water leaks in that area have been known to cause a host of issues months after the fact - I suspect as corrosion builds up.

Not sure how far you can pull it out while having everything connected except that one connector. If you can just remove the one connector and can get to the backside of the CJB, you could probe the pin on the CJB to see if your getting voltage. That would rule out a short to power somewhere else between the CJB and the rear tailgate area.

I doubt its a programming error, but I guess anything is possible.
Hypothetically, if I were to remove enough of the lower dash to gain better access to the CJB, and if I find pin 27 has power indicating a short, what would I do? I'm definitely concerned about making things worse with my rudimentary understanding of wiring.

Would I want to replace the pin connector, or try to chase the wire back to the BCM and isolate the physical location of the short?
 

Tbh1981

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Update: wiper works normally now. I blame literal gremlins for this one. See the video

 
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jlglr4

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Glad it’s fixed, and hope it doesn’t show up again.

As for voltage at the wire when the wiper is off, I wonder if you are reading the pink/grey wire instead of the purple/grey wire. Might be tough to tell them apart. The pink/grey is power - that should show 12v all the time. The purple/grey is the signal - that one should only have voltage only when the wiper is turned on. At least, that‘s my read of the diagram.

Seems like a short at the BCM plug - possibly moving the junction box fixed it. A short at the relay connector is another possibility.
 

greiswig

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I was going to say, have you measured 12V at TWO terminals there, or only one? Because one possibly should have power all the time, and it's the ground that gets switched. It's if you have two showing power all the time that there would be an issue.
 

jlglr4

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So, weirdly, the pink/grey power line on the diagram splits into two pins. So, looks like both pink/grey power line pins would have power all the time. I think you would need to probe specifically that purple/grey pin to tell.
 

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