I have a 2000 Accord EX and the center dome light will not come on when any door is opened. The light comes on when I switch it to the ON position, but not the DOOR position. Someone said it's the passenger side multiplex control unit. Is this correct?

 

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 :

• 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.

 

Yes, I think it is the passenger side MCU. The guy I bought it from also says that's the reason the remote starter is not working. The light does come on when I switch it to the ON position. So I'll stop by the auto wreckers to see if they have any MCU's I can pick up. Do you have any links to instructions on how to replace the passenger side MCU? Thanks!

 

It just unplugs from the passenger side fuse/relay box. There is one wire harness connector to unplug, then pry/pull the passenger mcu off the fuse/relay box connector.

 

So I do not need to take the dash apart where the glove box is then?

 

You have to remove a few other covers and the passenger side lower dashboard cover off first.

 

Got it, thanks! Now I just need to find an MCU!

 

Be careful, not all 6th generation Accord passenger side MCU are compatible with your 2000 EX. You may lose remote trunk release with the wrong one.

 

Okay, thanks for the heads up.

 

I'll take a look, but I think the previous owner screwed up the wiring in the passenger side fuse box. When I unlock/lock the doors, the dome light flickers so I think it's a wiring problem.