Hello All,

I checked the search and have spent the morning surfing google to no avail, so I figured I'd join and ask the question I would like to know. I am helping a friend with his 1999 Honda Accord, with the 2.3L 4 banger. He installed a radio on his own several months ago, and since then well he's had no dash lights. 10 minutes on google and it seems that this is the cause of killing the multiplexer.

The problem I am actually assisting with though is, he has rough unsteady idle once warm and has a MIL light. He had taken it to Autozone to have the code read and they feed him some manure on a fuse is blown I can't read the code (This is when he brought me in.) Seems they were right about not being able to read codes, I have triple checked all three fuse panels and every single fuse is good. Using both a scanner and the method described in the Haynes' manual it refuses to read the code out, so I cleared it by pulling the "clock backup fuse" and it has returned. I know through electrical testing that his EGR switch has tested open for both positions (indicating a bad switch is my assumption), but I am also later going to pull the IAC valve and clean it up and bench test it for operation.

Finally my question:

Does the driver side multiplexer dictate/control the bus for the MIL codes?

Thanks In Advance,

Dan

 

The mulltiplex integrated control units (micu) shouldn't control/dictate the bus for the ECU OBD-II trouble codes.

Here are some excerpts describing the earlier Honda systems (not all may be applicable to your friend's model year Accord trim level):

Multiplex control system consists of door, driver and passenger multiplex control units. If vehicle is equipped with Driving Position Memory System (DPMS), a driver’s power seat control unit is also included in multiplex system. These control units are integrated with each other using multiplex communication lines.

Multiplex control system includes engine oil pressure indicator circuit, seat belt reminder circuit, lights-on and key-in reminder, and key light timer circuits. Other controlled systems include dash illumination brightness control, entry illumination, automatic lights off system, power door locks, power windows and moon roof (with key-off timer operation), wiper/washers (with speed respondent intermittent wiper), security alarm system, interlock system and memory seat and mirror control.

MULTIPLEX COMMUNICATION FUNCTIONS
Multiplex control system reduces number of wire harnesses by
sending digital signals over shared multiplex communication lines.
Each multiplex control unit converts input signals from each switch to
digital signals, and transmits these as serial data signals.
Transmitted serial data signals are converted back to switch signals
by receiving multiplex control unit for switch operation. Dedicated
communication lines exist between door multiplex control unit and
driver’s multiplex control unit (Brown wire), and between driver’s
multiplex control unit, driver’s power seat control unit and
passenger’s multiplex control unit (Pink wire).

Driver’s multiplex control unit switches:
* Brake light switch.
* Instrument cluster lights brightness control.
* Driver’s door switch (OPEN).
* Driver’s seat belt switch (BUCKLED).
* Hood switch (OPEN).
* Engine oil pressure switch (DISCONNECTED/RECONNECTED).
* Headlight switch (PARK/TAILLIGHT).
* Ignition key switch.
* Keyless entry transmitter (LOCK).
* Keyless entry transmitter (UNLOCK).
* Keyless entry transmitter (PANIC).
* Parking brake switch.
* Tailgate latch switch.
* A/T gear position switch (PARK).
* Windshield wiper/washer switch, except MIST switch.