2003 HONDA CIVIC multiplex control unit under dash

Wipers/Washers
Component Location Index
WINDSHIELD WIPER MOTORTest, page 22-'143Replacement, page 22-145
WINDSHIELD WIPER ARMS and LINKAGEReplacement, page 22-'145
WIPER/WASHER SWITCHTest, page 22-140Replacement,page 22 140
UNDER.DASHFUSE/RELAY BOX
INTERMITTENT WIPER CIRCUITlln the multiplex control unit)Input Test, page 22-138
22-134

Control Unit Input Test
l.Before testing, troubleshoot the multiplex control system lsee page 22-jj2).
Remove the dashboard lower cover,
Disconnect the under-dash fuse/relay box connectors B, G, J, X and y
NOTE: All connectors are wire side of female terminals.
UNDER-DASH FUSE/RELAY BOXCONNECTOR B I6PIUNDER.DASH FUSE/RELAY BOXCONNECTOR G {1OP)
2.
3.
UNDER-DASH FUSE/RELAY BOXCONNECTOR J {8PI
l-,1 - llTtlF_j-JF-#
141516 7l8l
WHT/BLU
\
l-,1 - l-rl€ll
lslrlzlol
\BLU/RED
UNDER.DASH FUSE/RELAY BOXCONNECTOR X I8PI
4. Inspect the connector and socket terminals to be sure they are all making good contact.
. lf the terminals are bent, loose or corroded, repairthem as necessary, and recheckthe system.. lf the terminals are OK, goto step 5.
(cont'd)
BLU/WHT
BLU/BLK
22-141

Wipers/Washers
Control Unit Input Test (cont'dl
5. Reconnect the connectors, and make these input tests at the connector.
.lfanytestindicatesaproblem,findandcorrectthecause,thenrecheckthesystem.
.lfalltheinputtestsproveOK,themultiplexcontrol unit must be faulty. Replace the under-dash fuse/relay box
assembly.
CavityWireTest conditionTest: Desired resultPossible cause if result is not obtained
J4BLKU nder all
conditlons
Check for voltage to ground: . Poor ground (G501)
There should be 1V or less. . AnoDeninthewire
Y6BLKU nder all
conditions
Check for voltage to ground: . Poor ground (G502)
There should be 1 V or less. . An oDen in the wire
BIWHTiBLUlgnition switch ON
{ll) and washer
switch ON
Check for voltage to ground:
There should be battery
vortage.
Blown No. 20 (20A) fuse in the
under-dash fuse/relay box
Faulty wiper/washer switch
An open in the wire
E'0BLU/REDlgnition switch ON
(ll) and wiper
switch OFF (wiper
motor stopped)
Check for voltage to ground:
There should be battery
voltage.
Blown No. 20 (20A) fuse in the
under-dash fuse/relay box
Faulty wiper/washer switch
Faulty windshield wiper motor
An open in the wire
G7BLUA/VHTlgnition switch ON(ll) and wipers in
park position
Check for voltage to ground:
There should be battery
voltage.
Blown No.20 (20A)fuse in the
under-dash fuse/relay box
Faulty windshield wiper motor
An ooen in the wire
x1BLU/BLKlgnition switch ON(ll) and wiper
switch in INT
Check for voltage to ground:
There should be battery
voltage.
Blown No.20 (20A)fuse in the
under-dash fuse/relay box
Faulty wiper/washer switch
An oDen in the wire
\J
\J
L
22-142
J

6. Disconnect the M, P, K and J connectors from the underdash fuse/relay box, and make these input tests at the connectors.
.lfanytestindicatesaproblem,findandcorrectthecause,thenrecheckthesystem..lfalltheinputtestsproveOK,themultiplexcontrolunitmustbefaulty.Replacetheunder-dashfuse/relayboxassembly.
CavitvWireTest conditionTest: Desired resultPdsiblo c6use if result is not obtain€dK2BLU/ORNUnder all conditionsCheck for continuity betweenthe K2 terminal and the keylessreceiver unit 5P connectordisconnected:There should be continuitv.
An open in the wire
M7YEUBLKConnect J7 terminal to [,47lMgl terminal, and MglMTl terminalto J4
Check actuator operation:The driver's door lock actuatorshould lock lunlockl
Faulty driver's door lock actuatorAn open in the wireM9YEL
M6YEUBLKConnect J7 terminal to M6lMSl terminal, and M8lM6l terminalto J4
Check actuator operation:The passenger's door lockactuator should lock iunlockl
Faulty passenger's door lock actuatorAn open in the wireM8YEL
P16YELConnect J7 terminal to P17lP16l terminal, and P16lP17l terminalto J4
Check actuator operation:The hatch lock actuator shouldlock lunlockl
. Faulty hatch lock actuator. An open in the wireP17YEUBLK
-
22-157

Multiplex Control System
Component Location Index
IGNITION KEY LIGHTTest, page 22'91
lr, J
REAR CEILING LIGHTTest, page 22'96
LIGHT/SPOTLIGHTSTest, page 22-96
GAUGE ASSEMBLY
ECM
MULTIPLEX CONTROL UNIT{Built into the under-dashfus6/relav boxlTroubleshooting, page 22'172Input Test, page 22-175
22-168
t

ISystem Descriptions
The Multiplex Control System has four internal
functions:. Multiplexing (send multiple signals over sharedwtres). Wake up/sleep (runs at full power only on demand toreduce battery draw). Fail-safe (fixes or ignores faulty signals). Self-diagnosis (Mode 1 for the system, Mode 2 for
input lines)
The system controls the function of these circuits:. Entry lightcontrol (ignition key lightandceiting light). Wiper/washer intermittent wipe and park functions. Keyless/power door lock. Meter assembly, temperature gauge, and indicator
lights. HVAC (compressor and fan control). Key-in reminder. Headlight reminder. Seatbelt reminder
JI
/ar
22-171
Multiplex Communication
To reduce the number of wire harnesses, digital signals
are sent via shared multiplex communication linesrather than sending normal electrical signals throughindividual wires.. The input signals from each switch are converted todigital signals at the central processing unit (CpU).. The digital signalsaresentfromthetransmitting unitto the receiving unit as serial signals.. The transmitted signal is converted to a switch signalat the receiving unit, and it operates the related
component or monitors a swltch.. There are exclusive communicalion lines between
the ECM, the gauge assembly, and the under,dash
fuse/relay box.
Wake-up and Sleep
The multiplex control system has "wake-up" and"sleep" functions to decrease parasitic draw on the
battery when the ignition switch is OFF.. ln the sleep mode, the multiplex control unit stops
functioning (communication and CPU control) when it
is not necessary for the system to operate.. As soon as any operation is requested (for example, adoor is unlocked), the related control unit in the sleep
mode immediately wakes up and begins to function.. When the ignition switch is turned OFF, and the
driver's or front passenger's door is opened, then
closed, there is about a 10 second delay before the
control unit goes from the wake-up mode to the sleepmode.. lf any door is open, the sleep mode will not function.. lf a key is in the ignition switch, the sleep mode will
not function.. When in sleep mode, the draw is reduced from
70 80 mA to less than 10 mA.
Fail-safe
To prevent improper operation, the multiplex controlsystem has a fail-safe function. In the fail-safe mode,
the output signal js fixed when any part of the systemmalfunctions (for example a faulty control unit orcommunication line).
Each control unit has a hardware fail-safe function thatfixes the output signal when there is any CPUmalfunction, and a software fail-safe function thatignores the signal from the malfunctioning control unitand allows the system to operate normally.

Multiplex Control System
Troubleshooting
Mode 1 Tset
1. Remove the driver's dashboard lower cover {see
page 20-59).
2. Check the No. 9 ( 10A) fuse in the under-hood fuse/
relay box and the No. 10 (7.5A) fuse in the under-
dash fuse/relay box.
Are the fuses OK?
YES-Go to step 2.
NO-Find and repairthe cause ofthe blown fuse.!
3. Turn the ignition switch ON (ll).lf the driver's
seatbelt is unbuckled the seat belt reminder will
chime 6 times.
4. Set the ceiling light to the center position and close
allthe doors.
5. Connect the specialtoolto the multiplex inspection
conneclor.
6. After about 5 seconds the spotlight and ceiling light
should come on for 2 seconds, go out, then blink on
for 0.2 second to show the system is now in mode
1.
Did the spotlight and ceiling light indicate mode
1?
YES-Go to step 8.
NO Go to step 7.
22-172
-
7. Check for continuity between terminal 4ofthe
under-dash fuse/relay box connector J and body
ground.
ls there continuity?
YES Replace the under-dash fuse/relay box.l
NO - Repair the open in the wire.lf the wire is ok,
repair G301.1
8. lf ther are any DTCS present, the spotlight and
ceiling light will blink to indicate the DTC(S). lf more
than one DTC is present, the DTCS will be displayed
in ascending order, lf there are no DTCS the
spotlight and ceiling light will not blink again after
the mode 1 indication.
Are there any DTCg?
YES Go to step 9.
NO Go to the Mode 2 test.
9. Troubleshoot the DTC(S) in the order indicated
using the following charts.
lf a faulty control unit is suspected, substitute it
with a known food part and recheck for DTCS,
. lf the DTC(s) isstill present. go to the next step
listed for the DTC.. lf the DTC(S) is no longer present replace the
original part.

I
Individual
Multiplex
DTC
Probable Cause
The multiplex control unit cannot
receive signals from the gauge
assemDty.'lFaulty power or ground to thegauge assembly
2.Faulty gauge assemblv
3.Faulty under-dash f use/relay
box
The multiplex control unit cannot
receive signals from the ECM
1Faulty power or ground to the
ECM
2.Faulty ECM?Faulty under-dash fuse/relay
box
JInternal failure of the multiplex
control unit
1Faulty under-dash fuse/relay
box
5The gauge assembly cannot receive
signals from the multiplex control
unit and the ECM
Faulty power or ground to thegauge assembtv
Faulty qauge assemblv
6The ECM cannot receive signals
from multiplex control unit and thegauge assembty
1Faulty power or ground to the
ECM
Faulty ECM'
I
'Before replacing a Faulty ECM/PCM make sure ithas the latest software revision. UDdate if
necessary before swapping or replacing.
DTCs
Multiplex
DTC
Probable Cause
1,2 and 3
&
ECM DTC
P0600
Simultane
ously
Short to ground on one of the
communication wires.
Short to ground on the YEL wire
between the PCM terminal E24
and the under-dash fuse/relay
box terminal E10
2.Short to ground on the WHT/
GRN wire between the Gauge
assembly terminal A2 and
under-dash fuse/relay box
terminal K10
1and6
Simultane
ous ly
Open in the communication wire
IOpen in WHT/GRN wire
between the under-dash fuse/
relay box terminal K10 and the
Gauqe assemblV terminal 42
2and5
Simultane
ously
Open in the communication wire
1Open in the YEL wire between
the under-dash fuse/relay box
terminal E10 and ECM terminal
(cont'd)
22-173