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multiplex Control Unit

37K views 22 replies 10 participants last post by  luvmyhondas 
#1 ·
Long time reader and first time post.

So after hours of reading and weekends tracking down electrical problems, i have come to the conclusion that i need a new Multiplex Control Unit.

SO...without spending $300.00 at the dealer, where can i get one.
Secondly, what does this part look like?
Thirdly, If i go to the junk yard or buy a "Fuse Box" off of ebay (Ebay Link) will this contain the MCU?

Are the fuse-box and MCU different?

If you cant tell im a cheap-o and want to do it Myself

PS: here is the exact part number 38800-S0K-A02 (but cant find it online)

-Alex
 
G
#2 ·
Is "S0K" a part group number for the DC5? It's usually S6M or XM5 (transmission).

Also, what makes you think the multiplexer needs replacing? How exactly have you diagnosed this? Scan tool or just guessing? I'm not giving you a hard time, jut trying to get some insight into your issue. We've all wasted money of varying amounts trying to chase down electrical gremlins.
 
#3 · (Edited)
Well id rather not get into a whole long version of re-hashing whats wrong but here's the short version.

Changed out my dome light which was blowing a fuse all the time. Got a new assembly, which worked till i put in a larger (physical size) LED bulb which would short-out when i would go over large bumps (the actual positive Pin would touch the metal roof of the car)

After about 10 tries (aka #3 fuse blown under hood) with getting this to work (would work fine till i pressed hard on the bulb) i decided to just go back to the old bulb, now the automatic door position doesn't work....along with no auto hatch light, no "one push" automatic window, no auto turn on lights when locking the door.....few other small electrical problems.

ALL lights DO work in manual mode. After reading and researching im 99% sure its the MCU. So much for that "short version".

Point being, im unsure where to get (other then dealer) a MCU. I got that part number from another RSX thread but now im wondering because your right. Club RSX Thread

Orginal question still stands :pray:
 
#7 ·
I understand the need to know the full background, i really do.

Iv taken this to the dealer and know its the MCU. They already tested it in mode 1 and mode 2...each throwing out error codes (in the form of the dome light blinking). I just don't want to pay $300.00 for the part. :D
 
#8 · (Edited)
Mine was bad too. My problems included: the dash brake light staying on even with the e-brake released and the brakes are fine, power locks and keyless entry stopped working, door chime just stopped sounding. All the fuses and relays were good, so it pointed the the Multiplex unit that's built into the under dash fuse box. I have an '02 and swapped an '03 one in.
 
#9 ·
Thanks so much for the honest response. Yep, this fixed my issues to. For others who took the time to read the thread and are looking for answers

THe multiplex is the same as the whole fusebox. It cost me about 50 bucks at a junkyard. Also dont worry about labeling any of the 20something plugs, there all unique. Took about 15-20min to install.

SUPER Easy fix
 
#10 ·
MCU and AC

I have the same problems that were described above - No keyless entry, Break light sits on, and inside lights and door chime dont work. I am confident its also the MCU.

My question is: Could the MCU also be the problem for the AC not working. I have the service manual for the car, and in the electrical wiring diagram, the MCU comes before the AC pressure valve. So i am trying to figure out if that could be why the valve shuts off the hole AC system. None of the fans turn on and i checked all fuses. When I take out the relays and provide direct power to the compressor it works fine.

Please help if you can :)
 
#11 ·
I have the same problems that were described above - No keyless entry, Break light sits on, and inside lights and door chime dont work. I am confident its also the MCU.

My question is: Could the MCU also be the problem for the AC not working. I have the service manual for the car, and in the electrical wiring diagram, the MCU comes before the AC pressure valve. So i am trying to figure out if that could be why the valve shuts off the hole AC system. None of the fans turn on and i checked all fuses. When I take out the relays and provide direct power to the compressor it works fine.

Please help if you can :)
Im not sure about the AC unit, although like you said, it DOES go through there so its quite possible considering you have other electrical problems.

Secondly, what caused the MCU to malfunction. With me, i was carelessly blowing fuse after fuse....sooner or later the MCU just decided to stop doing its job.
 
#13 ·
I bought mine from the junkyard for $50.00. Also if you check online at ebay (acura fusebox) there running from $50 to $80.

Seriously tho....three posts above, shows evidence against your claim. Also, just telling someone that a part is expensive doesn't help AT ALL.
 
#16 ·
Hi Coffeeman,
I have been reading your posts and they have been very helpful. It appears that I have similar problems with my 2001 honda civic. You had mentioned that the multiplex unit is the same as the fuse box, is that the interior/Dash fuse box you are talking about because honda civics have two (one under the hood and the other in the dash)? And does it matter whether I get a multiplexer from '02 or '03? Thanks in advance. I am just very frustrated.
 
#21 ·
Still having Issues?

Hey all,
I know this thread is old, but my 2003 "Auto" is having this same issue I believe?
I did the mistake of taking to the "Stealership" first and come to find out they charged me to have an $860 alternator replaced, which did not fix the issue?

So I bought a used Multiplexor with in cabin fuse box for an 2004, hooked it all up and the car ran great for exactly one day before the symptoms came back, (clicking in the shifter while car is in park and idling like crap) along with "flashing" P,N,R,D indicators and "Brake" lamp?
My general question is, would anyone know what else absolutely needs to be checked in order to fix this issue?
I still have not replaced the solenoid in the center console as of yet?

I need any and all suggestions please as I need my car back on the road ASAP.
Thanks all.
 
#23 · (Edited)
Glad I found this! It appears that my 02 Type s just had a mcu fail. Clutch MC went bad, so it sat in my driveway for a couple weeks until I had time to work on it. Got in it after sitting all that time and keyless doesn't work, door lock switches don't work, dome light only works if manually switched on, and "brake" light is on without the parking brake pulled (fluid is full). Fuses are all good and the radio holds memory too. Luckily, I have the under dash fuse box from a 2004 I parted out just sitting on the shelf. I'm going to cross my fingers that it also solves my AC compressor being inop (even with proper freon charge)! Wish me luck! Btw, this happens the day I decided I was going to put it up for sale!
 
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