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Discussion Starter #1 (Edited)
My fresh out of warranty 2018 EX-L is having an electrical problem.

[EDIT by the OP ] I have changed this part of my post due to learning a lot more about my vehicle VIA schematics and more thorough troubleshooting. I didn't want anyone chasing something that was not correct.

I first noticed something was wrong when the "auto lock walk away" feature stopped working. Further troubleshooting has revealed:
1) The "auto lock walk away" feature is not functional.
2) The sunroof is not functional.
3) The passenger door window is not functional.
4) Both of the rear view mirror defrosters are not functional.
5) All fuses in the engine compartment and the interior were checked. No blown fuses were found.
6) All buttons on both remotes work except the remote start. The long-press feature to open all windows and the sunroof no longer work.
7) The rear hatch works normally via the remote or the button on the dash. However, the exterior hatch button only works if the engine is off.
8) When car is locked via key fob, there is no beeping or light flashes to acknowledge it is locked. When car is unlocked via key fob, the lights flash but there is no beep.
9) If the van is locked and you touch a door handle, there are two beeps and it unlocks. This is the only time beeps happen anymore.
10) The door lock button on the passenger door never works. The door can be locked/unlocked from the driver's door switch or a remote.

My dealer says a computer scan revealed that the car's security system will not engage. They suspect the body control module (BCM) may have a problem, but they claim they are on back order right now. They say that if a replacement BCM doesn't fix this, the next step will be to search for a defective connector. The HondaCare extended warranty will not cover the labor for that (estimated @ $1,500+) to do that, only replacement parts.

I'm not confident in the "connector theory" because so many unrelated components are only cripled logically, but are not dead electrically. In the meantime, am I overlooking something or can a blown BCM make things this crazy?
 

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Have you tried pulling the battery out, fixing the mirror (if hadnt been done) and then reinstalling the battery to re-test?
 

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Discussion Starter #3
I have
Have you tried pulling the battery out, fixing the mirror (if hadn't been done) and then reinstalling the battery to re-test?
I have not taken the battery out, but I have disconnected the positive lead for 10 minutes or so. There is a dedicated feed from the positive lead of the battery for the BCM (body control module). I am assuming power is getting to the BCM because the vehicle does appear to receive some functionality from the BCM. Is there something I could gain by removing the battey as opposed to just disconnecting it?

The mirror glass has been replaced. The rest of the mirror assembly is undamaged. The Honda part number for the mirror was checked against the vehicle's VIN as per a request from the parts guy at my Honda dealership. Apparently there are some variations of them.
 

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I should have been clearer; disconnecting the negative and positive cables from the battery should essentially 'reset' the electrical system. If you have factory entertainment unit, keep the codes handy prior to this exercise. They use the VIN to ensure the part properly conforms to the trim of the model and includes factory installed options.

If this power loss is happening after the mirror episode, disable the heating by pulling its respective fuse and relay. See if the power loss is still present. It would not hurt to get the battery load tested, by itself, at Autozone or someone similar.

Pull all the relays in the fuse/relay boxes and bench test them. Hope you have access to the repair manual as input voltages for testing may not always be 12V.

Electrical shorts and surges do create havoc in systems. That minor spark in your heated mirror line, could have triggered something nasty that peeked its head after some time.
 

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The passenger side mirror defogger is powered by the "Front Passenger Power Window Switch"; Can you also check if you have power on #39 fuse - that seems to power front passenger power switch. Maybe you burnt that switch up (try disconnecting it and see if anything else starts functioning).
Looking at circuit schematics, for #11, #12, #13, and #14 --> check the following fuses #38 (same compartment) and #27.



My fresh out of warranty 2018 EX-L is having an electrical problem. It started within a day or two from when I was replacing a broken passenger side mirror glass. I noticed a spark when the two (un-insulated) slide connectors for the mirror's heating element touched for a moment. I swear the car was off at the time, but I could be wrong...that was several days ago.

[EDIT by the OP I am now certain the car was not powered on. I grew up on a farm, and have been repairing my own things nearly all of my 60 years. I just don't make those kinds of mistakes anymore. I distinctly remember looking at those two bare connectors and grabbing a pair of insulated pliers to pull them off. Plus, even if the car was on, you have to activate the rear window defroster to energize the mirror defrosters. I live in the deep South and it was in the 60's the day I replaced the mirror. In fact, I have a garage so I don't think I have ever used the defroster! So where could that spark have come from?]

I first noticed that the "auto lock walk away" feature stopped working. Further troubleshooting has revealed:
All buttons on both remotes work except the windows and sunroof do not open while long-pressing the unlock button.
Sunroof: Not functioning at all.
Rear hatch: Hatch button works to open the hatch only if engine is off.
Rear view mirror defrosters: Both of them have stopped working. No power to the heater wires on the glass. Mirrors tilt properly. Rear glass (tailgate) defroster is working.
When car is locked via key fob, there is no beeping or light flashes to acknowledge it is locked. When car is unlocked via key fob, the lights flash.
Passenger door window will not respond from passenger door window switch or from driver-side switch.
Passenger door will not lock from passenger door switch. It will lock from the driver-side switch. Key for will lock it too.
Remote start no longer works.

I have double checked all fuses in the interior, engine, and rear compartments. No fuses were blown. However, in the interior fuse box A, fuses # 11 (Driver door lock), # 12 (FP door lock), # 13 FP door unlock, # 14 (Driver's door unlock) and # 26 (RP Door unlock) never have power to them regardless of the "power state" of the vehicle. There has got to be a relay or fuse common to all this somewhere, but I can't find it!

The dealer says a computer scan revealed that the car's security system will not engage. They suspect the body control module may have a problem, but there are back orders on them right now.

I have reset the entertainment system, removed & reinstalled fuse # 37 (Audio system), and removed the positive battery cable for 10 minutes or so.

The big mystery so far is that, according to a lack of power to fuses # 11 and 14, the driver door should not be locking and unlocking electrically. I am 99% sure I have the fuses correctly identified, but there is always room for an error, right?

Am I overlooking something, or can a blown BCM make things this crazy?
 
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