2000 Accord EX and the center dome light will not come on when any door is opened
#11
05-27-2016, 01:56 PM
EX is slightly different than DX and LX trim.
The ceiling light (aka dome light) have dual functionality; (1) turns on if manually switched to ON, or (2) turns on if door opened. Because the ceiling light have "dual functionality" there are two separate ground sources involved in the circuit. (1) When ceiling light is switched to ON, the light switch get its ground source from the base of the unit. (2) If a door is opened, the light switch gets the ground source from the door switches via wiring that goes through the Passenger side Multiplex Control Unit (MCU) located at the passenger side fuse/relay box and onward to the ceiling light. – All the individual doors switches (at each door) are wired into the passenger MCU.
LX and DX trim levels: All the individual doors switches (at each door) are wired directly into passenger MCU.
EX trim level: Driver's door switch and left rear door switch are wired into driver side MCU (located in driver side dash fuse/relay box), then run through a pink communications wire between the driver and passenger MCUs. However, the ground will still then be running from the passenger side MCU to the ceiling light. Passenger front and right rear door switches are wired directly into passenger MCU.
The issue may be due to :
The ceiling light (aka dome light) have dual functionality; (1) turns on if manually switched to ON, or (2) turns on if door opened. Because the ceiling light have "dual functionality" there are two separate ground sources involved in the circuit. (1) When ceiling light is switched to ON, the light switch get its ground source from the base of the unit. (2) If a door is opened, the light switch gets the ground source from the door switches via wiring that goes through the Passenger side Multiplex Control Unit (MCU) located at the passenger side fuse/relay box and onward to the ceiling light. – All the individual doors switches (at each door) are wired into the passenger MCU.
LX and DX trim levels: All the individual doors switches (at each door) are wired directly into passenger MCU.
EX trim level: Driver's door switch and left rear door switch are wired into driver side MCU (located in driver side dash fuse/relay box), then run through a pink communications wire between the driver and passenger MCUs. However, the ground will still then be running from the passenger side MCU to the ceiling light. Passenger front and right rear door switches are wired directly into passenger MCU.
The issue may be due to :
- Faulty passenger MCU
- Intermittent open (break) in the Blk/Wht wire for the ground source (-) coming from the MCU to the ceiling light. -- Less likely.
- Intermittent open (break) in the Wht/Blu wiring for the power (+) coming from passenger side Fuse No. 11 (7.5A). -- Less likely.
- For EX: Faulty driver MCU (unlikely; but, can't rule out completely)
- For EX: Pink communication wire between driver and passenger MCU (unlikely; but, can't rule out completely)
- Since the ceiling light doesn't turn on when switched ON, there can also be an issue with the ceiling light itself and/or the previous items mentioned.
So I have put this off since we last spoke. I am going to try and fix this problem over the weekend, so hopefully you can respond before then with any insight.
I did a preliminary test yesterday... I noticed the previous owner cut out some of the wire covering on the Blk/Wht ground wire going into the passenger fuse unit that runs up the arm to the light. He spliced some other small wire into which I haven't figured out where it's going right now (I will this weekend). So I took another piece of wire, attached it to the exposed piece of the Blk/Wht wire and then grounded it and the ceiling light came on. So I now know 100% the wire running from the MCU/fuse panel to the light is working. The light also comes on when I manually switch it to the ON position, so the Wht/Blu wire is fine as well.
Since opening either of the passenger side doors does not turn the ceiling light on, I am left to believe it is a faulty passenger-side MCU. Would you agree to this? I am going to visit the autowreckers this weekend to grab another passenger MCU and see if that works. What do you think?
The only other thing I found was this picture someone posted about the printed circuit board being damaged when an aftermarket security system has been installed, which my car has (see picture). The only problem is that the middle 14P connector does not have a Blk/Wht wire??
Last edited by badlt; 05-27-2016 at 02:03 PM. Reason: Added image
#13
05-28-2016, 12:07 PM
Yep, all four courtesy light s come on. As well, the red "door open" lights also work on the dashboard cluster panel when any door is opened.
#14
05-29-2016, 04:00 PM
Yeah baby!!!! Got it working!!! Went to the auto wreckers and picked up a passenger side MCU for $20, installed it, and now the interior dome light works as it should:
- With key in the ignition, dome light comes on when any door is open, and then immediately shuts off when the door is closed
- When there is no key in the ignition, the dome light comes on when any door is opened, and then dims out about 10 seconds after the door is closed
LOVE IT!!!
- With key in the ignition, dome light comes on when any door is open, and then immediately shuts off when the door is closed
- When there is no key in the ignition, the dome light comes on when any door is opened, and then dims out about 10 seconds after the door is closed
LOVE IT!!!
#16
09-12-2019, 04:30 PM
Hey everyone.
I just bought a multiplex RH and I'm assuming the seller knew it was faulty. Regardless, this is my 3rd one that's shot. Does anyone have schematics to the PCB to repair it or any links to threads about this?
Thanks a million. Can't wait to have a dome light again.
I just bought a multiplex RH and I'm assuming the seller knew it was faulty. Regardless, this is my 3rd one that's shot. Does anyone have schematics to the PCB to repair it or any links to threads about this?
Thanks a million. Can't wait to have a dome light again.
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