Driver's Multiplex Control Unit

Remove the driver's multiplex control unit from the driver's under-dash fuse/relay box.
Inspect the connector and socket terminals to be sure they are all making good contact.
- If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system.
- If the terminals look OK, go to step 3.
  DRIVER'S UNDER-DASH FUSE/RELAY BOX SOCKET (Driver's multiplex control unit connector A)
  
  Fig 1: Identifying Driver's Multiplex Control Unit Connector A
  Courtesy of AMERICAN HONDA MOTOR CO., INC.
  
  DRIVER'S MULTIPLEX CONTROL UNIT CONNECTOR B
  
  Fig 2: Identifying Driver's Multiplex Control Unit Connector B
  Courtesy of AMERICAN HONDA MOTOR CO., INC.
  
  DRIVER'S UNDER-DASH FUSE/RELAY BOX CONNECTOR J
  
  Fig 3: Identifying Driver's Under-Dash Fuse/Relay Box Connector J
  Courtesy of AMERICAN HONDA MOTOR CO., INC.
  
  DRIVER'S UNDER-DASH FUSE/RELAY BOX CONNECTOR M
  
  Fig 4: Identifying Driver's Under-Dash Fuse/Relay Box Connector M
  Courtesy of AMERICAN HONDA MOTOR CO., INC.

With the driver's multiplex control unit still disconnected, make these input tests at the connector and driver's under-dash fuse/relay box socket.

If any test indicates a problem, find and correct the cause, then recheck the system.

If all the input tests prove OK, go to step 4.

CONTROL CIRCUIT INPUT TEST REFERENCE

Cavity	Wire	Test condition	Test: Desired result	Possible cause if result is not obtained
A12	Fuse/relay box socket	Under all conditions	Check for voltage to ground: There should be battery voltage.	Blown No. 13 (7.5A) fuse in the passenger's under-dash fuse/relay box Faulty driver's under-dash fuse/relay box An open in the wire
A14	Fuse/relay box socket	Under all conditions	Check for continuity to ground: There should be continuity.	Poor ground (G401) Faulty driver's under-dash fuse/relay box An open in the wire
B3 B4	ORN/WHT and WHT/YEL	Adjusting dial rotated	Check for resistance between the B3 and B4 terminals: There should be 0-20 kohm as the dial is rotated.	Faulty dash lights brightness controller An open in the wire

Reconnect the driver's multiplex control unit to the driver's under-dash fuse/relay box, and perform the following input tests at the appropriate connectors on the driver's under-dash fuse/relay box.

If any test indicates a problem, find and correct the cause, then recheck the system.

If all the input tests prove OK, the driver's multiplex control unit must be faulty; replace it.

CONTROL CIRCUIT INPUT TEST REFERENCE

Cavity	Wire	Test condition	Test: Desired result	Possible cause if result is not obtained
M3	RED/BLK	Combination light switch ON (Parking or Headlight position)	Check for voltage to ground: There should be battery voltage.	Blown No. 54 (40 A) fuse in the under-hood fuse/relay box Blown No. 10 (15 A) fuse in the passenger's under-dash fuse/relay box Faulty taillight relay Faulty combination light switch An open in the wire Faulty driver's multiplex control unit (EX and EXL)
J6	RED	Combination light switch ON (Parking or Headlight position), set dash lights brightness controller to minimum setting	Attach to ground: Dash lights should come on full bright.	An open in the wire
B3 B4	ORN/WHT and WHT/YEL	Combination light switch ON (Parking or Headlight position)	Jump wire from B3 to B4: Dash lights should come on full bright.	An open in RED wire Faulty driver's multiplex control unit (EX and EXL) Faulty driver's under-dash fuse/relay box