2002 HONDA CIVIC Workshop Manual

Multiplex Control System
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Circuit Diagram (cont'd)
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IwHTPLU
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lE lnv*-| > | ucHT
lA l'*'tYl
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CIILING LIGHT
I.l|MOBItEER@NTIOL UIIITRECEIVEE
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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
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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.
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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.

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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'
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'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)
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IMultiplex Control Unit Input Test
Remove the driver's dashboard lower cover (see page 20-59).
Disconnect the under-dash fuse/relay box connectors C, E, F, J, K, O, p, O, X and y.
NOTE: All connectors are wire side of female terminals.
CONNECTOR C {14P}CONNECTOR E I13P)
1.
2.
CONNECTOR F {12P}
GRN/RED {USAIGRN/ORN (Canada)
coNNECTOR P (18P)
CONNECTOR J {8PI
WHT/RED
123
4561
BLK
{cont'd)
GRN/ORN BLU
CONNECTOR K {17P)
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CONNECTOR O I12P)
CONNECTOR X {8P)CONNECTOR O (8P}
LT GRN/RED GRN/ORN
CONNECTOR Y {13P)
BRN/YEL
BLU/REDBLU/RED
345
67E10 )./12
YELGRN/RED
12457
810/V,/ l,/
WHT/GBN
3567I
,/1,/l,/121517
REDGRN/RED
WHT/BLK
RED/WHT
23,/1,/
618r012
BLK
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Multiplex Control System
Multiplex Control Unit lnput Test (cont'd)
3. Inspect the connector and socket terminals to be sure they are all making good contact
.lftheterminalsarebent,looseorcorroded,repairthemasnecessary,andrecheckthesystem. llthe terminals look OK, go to step 4.
4. Reconnectthe connectorstothe under dash fuserelay box, and make surethese inputtests atthe appropriate connectors on lhe under-
dash fuse/relav box.
. lf any test indicates a problem, {ind and correct the cause, then recheck the system. lf allthe input tests prove OK, the multiplex control unit must be faulty. Replace the under_dash fuse/relay box assembly
CavitvWireTest conditionTest: Desired .esult r Possible cause if resullE qS!q!!e!!ed
J4BLK[J nder all conditionsCheck {or voltage 1o ground:Therc sholl.l he 1V or lessPoor ground (G20'l)An ooen in the wire
Y6BLKlJnder all conditionsCheck for voltage to ground:There should bc 1 V or less.Poor ground 1G501)An ooen in the wire
Y1BFNryELParking brake leverdown, turn theigntion switch ON (ll)
Check for voltage to ground:There should be battery voltagewhile the Brake system indicator ison forthe buld check.
An open in the wireShortto groundFaulty ABS modulatorcontrol unit
Check for voltage to ground:There should be 1V or less when the
J2WHT/REDUnder allconditionsCheck for voltage to groundiThere should be baftery voltage.Blown No.9 (10A)fuse in the under'hoodfuse/relay boxAn oncn in rhc wire
CavitvTest conditionTesi: Oesired resultPossible cause ifresult is notobtained
o3GRNDriver's door openCheck for voltage to ground:There should be 1 V or less-Faulty driver's door switchAn ooen in the wire
Driver's door closedCheck for voltage to ground:There should be 5 V or more.Faulty driver's door switchShort to qround
O4LT GRN/REDPassenger's doorCheck .for voltage 10 ground:There should be 1 V or less.Faulty passenger's door switchAn ooen inthewire
Passenger's doorCheck for voltage to ground:There should be 5 V or more.Faulty passenger's door switchShort to oround
osI]l.l
4.,
F1
F8
GRN/ORN
GRN/ORN
GRN/RED(USA)GRN/ORN(Canada)
Parking brake leverCheck for voltage to groLrnd:There shorl.l be 1 V or less.Faulty parking brake switch. An ooen in thewireCheck for voltage to ground:There should be 5 V or more.
. Faulty parking brake switchShortto ground
o5BLU/REDlgnition switch ON (ll),
driver's seat belt isCheck for voltage to ground:There should be 1V or less.Faulty driver's seat belt switchPoorground (G551)An oDen in the wire
Q6BLU/REDlgnition switch ON (ll)
driver's seat belt isbuckled.
Check {or voltage to ground:There should be 6 V or more.Faulty driver's seat belt switchShortto ground
P18RED
H",=
Check for voltage to ground:There sho0ld be 1V or less-
f -9*:li:'^:**:':s*:*
Faulty hatch latch swrtchPoor ground (G552)An open in the wireFaulty hatch latch switch
X5lgnirion key in the Check for voliage to gtound:ignit on switch Thpre should be I V or lcss
lgnrtron kev our o{ the Check for vollage to ground:
. Faulty ignition key switch. Poor ground (G401). An open in the wire
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CavitvWireTest conditionTest: Desired resultPossible cause if resuk is not obtainedX8WHT/BLKUnder allconditionsAttach to ground:The ignition keylight should come on.Blown No.3 (7.5A)fuse in the under,hood
Blown LEDAn ooen in the wireo7GRN/REDCeiling light switch inthe middle position,all doors closed
Attach to ground:The ceiling light,spotlights should come on.Elown No. 3 (7.54)fuse in the undeFhood
Faulty ceiling lightAn oDen in the wirec]1BLU Under all conditionsAttach to ground: Dash lights shouldBlown No. 2 (15Aifuse in the under-hoodfuse/relay boxFaulty taillight relayAn ooen in the wireF8GRN/REDBrake fluid reservoirfloat in downposition (brake fluid
Check for voltage to ground:There should be less than I V.Faulty brake fluid level switchAn open in the wire
Brake lluid reservoirfloat in up position(brake fluid at fulllevel)
Check for voltage to ground:There should be 5 V or more.Faulty brake fluid level switchShortto ground
E10YELUnder all conditionsCheck for voltage to ground:There should be battery voltage inthe sleep mode and 3 Tvoltswhen
. An open or short in the wire
K10WHT/GRNUnder all conditionsCheck for voltage to ground:There should be battery voltage inthe sleep mode and 3 Tvoltswhen
An open or short in the wire
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