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Hi guys, I am seeking some help with my 2015 pilot. About 4 weeks ago, the battery died so I assumed it was a bad battery. Went to autozone, they tested it, said it was fine. Battery is only 6 months old.

Dead battery again. Took it into my local mechanic, they tested the alternator and battery and said both are functioning great and said nothing is wrong with my car.

Took it home, dead battery the next morning. Jumped it, took it back. They did a parasitic draw test, determined it was a bad AC relay. Replaced that. Took it home.

Dead battery the next morning. Took it back and mentioned I had read online it might be a radio going bad and to test all the fuses (like I had read online, I'm a mom and I know nothing about cars). They said oh yes, it's a bad radio, we can't help you, take it to Honda.

Took it to Honda. Told the tech all this previous back and forth, he did a draw test and it tested perfect, not a single thing wrong. He said it might be that my kids stuck coins in the CD or DVD player and they are conducting electricity. Tested that, nope. It sat for 3 days at Honda, then started right up so he said, nothing is wrong with your car. I took it home, it's been working great for a week.

Then this morning I go to start it up again, dead battery. At least this time it lasted a week. I'm at my witts end. I have no idea where to turn now, I can't seem to duplicate this problem for the mechanics, any ideas?? They have tested the battery voltage and said it holds steady and is even more charged than it should be. No one can figure this issue out, so I thought I'd see if any of you had any ideas for me to tell these mechanics.
 

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There's an AC relay that burns, sticks, and drains the battery. A quick search here will get you the details.

The compressor clutch relay is in the main under-hood fuse and relay panel, the sorta-triangle shaped box on passenger's side of the engine bay midway for and aft. The cover comes off with a few little holding tabs. The relays are identified on a label inside the cover. There are 11 relay sockets in a bunch on the rear fender side of the panel. The AC clutch relay is on the drivers-side end of the second row from the rear. Listen carefully as you pull that relay -- if it is stuck closed, you should hear the compressor clutch clink open as you lift out the relay. Regardless, go ahead and replace the relay as it's a known weak spot in the system. Buy a good relay to put in there, avoiding the cheap no-names you might find at a bargain parts place. IMO it's probably worth spending at the dealer parts counter to get a top-quality piece.

There's a slew of troubleshooting fun to enjoy trying to diagnose the sometimes-sticking relay. Just replacing it is faster and a whole lot easier.
 

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2016 CRV Touring AWD, 2005 Pilot RIP.
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Kids hitting the switch for an interior light?

honestly, if you don't have a mechanic willing to do the work to track it down, then you need to get a meter and pull the fuses one by one until the draw disapp
 

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There's an AC relay that burns, sticks, and drains the battery. A quick search here will get you the details.

The compressor clutch relay is in the main under-hood fuse and relay panel, the sorta-triangle shaped box on passenger's side of the engine bay midway for and aft. The cover comes off with a few little holding tabs. The relays are identified on a label inside the cover. There are 11 relay sockets in a bunch on the rear fender side of the panel. The AC clutch relay is on the drivers-side end of the second row from the rear. Listen carefully as you pull that relay -- if it is stuck closed, you should hear the compressor clutch clink open as you lift out the relay. Regardless, go ahead and replace the relay as it's a known weak spot in the system. Buy a good relay to put in there, avoiding the cheap no-names you might find at a bargain parts place. IMO it's probably worth spending at the dealer parts counter to get a top-quality piece.

There's a slew of troubleshooting fun to enjoy trying to diagnose the sometimes-sticking relay. Just replacing it is faster and a whole lot easier.
I found this video helpful if you don't want to throw money at parts. (Self Guilt)
"Honda Relay Testing"
 

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NG --

I'm normally of the same interest and persuasion. I check everything and analyze for failure modes. Sometimes, as in this case with the clutch coil, the perfect replacement relay would have a suppressor diode integrated with the load contacts to limit arcing each time the contacts open. But we're not trying to re-engineer the system as much as diagnose the parasitic leakage problem.

For the average user, the fun of setting up the tests is less than the $fun of just plugging in a new relay.

Several of the threads in Piloteers talk about listening for the clutch to release with a click or clack when you pull the relay. The relay may allow current leakage at rate that's less that what's needed to actually engage the clutch, but still high enough to drain the battery overnight. Normal operating current for similar clutch coils is typically in the 3 to 5 amp range, so a small leak (~1A) through the relay may not actually draw the clutch closed. By the OP's description, his problem is intermittent, so bench testing the old relay with power supply and a meter might not give you a definitive answer.

For sure the OP should check to see if lights interior lights are left on after the car is stopped and all doors have been closed. That would imply a change in user patterns, not impossible so worth the look for lights on. Meanwhile, the symptom matches a well-known failure mode with the AC clutch relay. The simple and inexpensive test is to try a new relay there and see if the battery-drain symptom disappears.
 

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I bought a used 2010 Pilot which the dealer always had running for me when I drove it, and upon leaving the lot with it. From the beginning it had a dead battery after it sat for any amount of time. The "compressor clutch relay" turned out to be one of the most common problems and failures for dead batteries in this vehicle so it was my first choice to fix. In the 2 years I've owned it, I've had to replace it twice. It has run like a dream otherwise. (As a note: I had absolutely never had problems with my air conditioner or heater at any time, so I really never would have guessed it would have been this relay.)
The original Relays off the manufacture line were mostly bad and would stick open after the engine was turned off and continue to drain the battery. I'm positive someone got tired of trying to track the problem down on the vehicle I bought and unloaded it... I got lucky, but it turns out it is such a common problem, I'd definitely start there first. O'Reilly's or Autozone usually have it in stock. It only cost $4-8 bucks, totally worth starting with! Good luck!!
 
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