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Discussion Starter · #1 ·
Checking the lights on my boat trailer yesterday, I noticed that the backup lights on my 2013 Pilot came on when I turned on my headlights. I unplugged the trailer and the backup lights still came on when the headlights were turned on. I have never noticed this before and have no idea how long it's been going on.

Any idea what's going on?

Thanks.
 

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Has the back of the car ever been "worked on"? Curious if the tail lights have been off and bulbs/holders mixed up on replacement.

The backup light bulb has a single-filament socket, with Blue and Black wires connected.

The backup light triggers when the transmission range switch indicates "reverse" position by grounding terminal F9 at the underdash fuse & relay panel. You can test continuity to ground in that connector by lifting it and testing with your DMM. White wire in that "F" connector, by the way,

The circuit is protected by fuse 10 (7.5A) in that panel. Fuse 10 sees power only when the key is in RUN or START position, so you could test some function by turning headlights on with key off or out completely. Regular tail lights and markers should come on. Backup lights stay off even with the gear selector in reverse.

There are no backup light connections to the trailer connector.
 

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Discussion Starter · #3 ·
No, the back of the car has never been worked on. I just noticed this yesterday...no telling how long it's been going on.
 

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Pull fuse 10 in the underdash fuse panel and see if the results are the same. Look closely to see if any other bulbs aren't lit when you do this if you see the backup lights stay on.

With key off, there is no power available to the backup lights circuitry. With the fuse removed, power is interrupted again to that circuit. If they stay on with headlights on, key off, and fuse 10 pulled, you most likely have bulbs swapped in the housings.

We are working on a US-market car, right?
 

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Discussion Starter · #6 ·
Pull fuse 10 in the underdash fuse panel and see if the results are the same. Look closely to see if any other bulbs aren't lit when you do this if you see the backup lights stay on.

With key off, there is no power available to the backup lights circuitry. With the fuse removed, power is interrupted again to that circuit. If they stay on with headlights on, key off, and fuse 10 pulled, you most likely have bulbs swapped in the housings.

We are working on a US-market car, right?
Yes, a US car.

I'll try your suggestion...thanks.
 

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Discussion Starter · #7 ·
Just pulled the #10 fuse and the backup lights still came on when I turned on the headlights.
 

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Discussion Starter · #8 ·
Disconnected the trailer plug - backup lights still come on.

Pulled the #10 fuse - backup lights still come on.

Installed all new bulbs in tail lights - backup lights still come on.

I give up...time to take it to the dealer and let them figure it out. :(
 

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I gave you some wire colors for the backup lights sockets, so you can identify the correct sockets. Are the sockets with just a blue wire and a black wire stuck in the backup-lights nacelle on the housings?

The relay function for the backup lights relies on having fuse 10 and the key in run or start. There is no other way that power will get to the backup light bulbs unless you melted some wiring in the car while dinking with your trailer lights hookup. The factory harness and the Honda-supplied retrofit harness both have fuses protecting the car from such dinking. Do you have the factory or the Honda-supplied retrofit harness? If another cheap aftermarket harness was fitted, damage to the wiring becomes a real possibility.

How comfortable are you doing some checking with a DMM through wiring harness connections?
 

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Discussion Starter · #10 ·
I gave you some wire colors for the backup lights sockets, so you can identify the correct sockets. Are the sockets with just a blue wire and a black wire stuck in the backup-lights nacelle on the housings?

The relay function for the backup lights relies on having fuse 10 and the key in run or start. There is no other way that power will get to the backup light bulbs unless you melted some wiring in the car while dinking with your trailer lights hookup. The factory harness and the Honda-supplied retrofit harness both have fuses protecting the car from such dinking. Do you have the factory or the Honda-supplied retrofit harness? If another cheap aftermarket harness was fitted, damage to the wiring becomes a real possibility.

How comfortable are you doing some checking with a DMM through wiring harness connections?
I'm no mechanic or electrician, so no, I'm not comfortable checking anything. I have an appointment on Friday to let the dealer figure out what is going on.

Thank you for your help...I appreciate it.
 

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Let us know what happens please. You can still pop the tail light housings off and verify that the bulbs with the blue and black wires are the ones in the backup holes. Hate to pay the dealer to find easy stuff.
 

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Discussion Starter · #12 ·
Took the car to the dealer this morning. Turns out there is a short in the fusebox and it's going to cost me $900 and change to fix it. :(
 

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That "fusebox" is the MICU, a somewhat-smart controller that includes a LOT of functions. It unplugs (about 8 connectors IIRC) and unscrews to change. Go boneyard hunting at a Pick-Your-Part yard.

And there is not a likelyhood that there's a "short in the fusebox". In our current car-repair world, "technicians" diagnose based on symptoms they read from a diagnostic list on a screen and proclaim that an expensive part will plug in and magically cure the problem. With fuse 10 removed, there is NO AVAILABLE CURRENT FLOW PATH through the MICU to the backup lights. Your symptom of backup lights with running lights points to a fault in the wiring between the MICU and the trailer plug. Their computer-based diagnostic system a makes no provision for wiring damage, only component testing based on symptoms.

You shared that you aren't comfortable doing the diagnostic work with a meter, and I understand that. But you might do a lot better dollars-wise taking the car to an independent shop or auto electrics place where they can unplug a connector at the MICU ("F" I believe) and test for continuity in the harness between the running lights and backup lights conductors in from that end. The next test point is where the trailer connector harness joins the body harness in the left rear interior just behind the wheelhouse.

Since the problem started when you were fiddling with the wires by the trailer connector, my nickel says you'll find a wiring fault in that section between the connector at the hitch and the interface in the left rear. Unplug that section and see if the problem goes away.
 
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