2003 HONDA CIVIC fan

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.

Service Manual lndex
)s
NOTE: Referto the lollowing listto look up A/C Pressure Switch CircuitDTCS, symptoms, fuses, connectors, wire Troubleshooting ......... ...-.-....-...-.-.-....-..21-32 Bharnesses, specifications, maintenanceschedules, and general serviceinlormation:
DTC Troubleshooting Indexes
A/C Signal CircuitTroubleshooting.........................-...... 11-'133 Back-up Light SwitchTest .......................................................... 13'3A/F lAir Fuel Ratiol SensorABS/TCS Components ........................ 19-34 Replacement ....................................... 1 1-113 Back-up Li9ht3EPS Components ................................. '17-22 Circuit DiagramFueland Emissions11-i A-Dillar Corner Trim
ABS Indicator Circuit
Heating/Ventilation ................................ 21-9 Replacement ...............-.....-..............-.... 20,96 Ball Joint BootssRS ........................................................ 23-28Replacement ......
... 19-52 Ball Joints
22-75
18 16
Remova1.............-.......... . ...........18-10Symptom Troubleshooting Indexes TroubleshootingABS/TCSComponents........................ 19 35Cruise Control System ..........................4 38 ABS Modulator-contml UnitEPS Components ................................. 17-23 Bemoval/lnstallation ............................ 19-57 BettervFan Controls10,12
Accessory Powor Socket Front
Blowor Pow€r Transistor
.......22 50
Blower UnitRemoval/lnstallation ............................ 21-39
Fuel and Em issions .............................. 11-10 ABS/TCS ComoonentsHeating/Ventilation..............................21 10 Component Location Index ................. 19-30 Beverage Holder
SRS ........................................................ 23'30 CircuitDiaqram.......................... 19'42Blower MotorReplacement .....21 41
21-38
Power 0istribution ...............................22-46 TesVReplacement .............................. 22'149Under-dash Fuse/Relay Box ............... 22 45Under-hood Fuse/Belay Box ...............22 44 Accessory Power Sockets
Fuse/Relay lndexes
(to harness)
Connector and Wire Harness lndexesComponent Connectors
Circuit Oiagram .................................. 22-149
Air Cleaner......2214 Rep1acemen1.....................................11-162
Air MixControl MotorMeintenence section .................... Section 3 Replacement ......................................... 21'34 Brake CelipersTest......................21-34 Overhaul19-14,23Gene.al lnlormation section........ Section 1
21.57
Airbag. Driver's
Ahernator FR Signal CircuitTroubleshooting .... .........-..........11 134
AntennaReplacement
Inspection ............................................. 19-24Rep|acement................. .................... 19-25
Bieke Meder Cylinder
Irake Discs
A
Replacement ....................................... 23 1 'l3 Inspection .................... ................... 19-13,22Repair ...........-...................................... 23 1 16Brake Fluid Level SwitchAirbag. Front Passenger's TestBeplacement....................................... 23-1 14AIC Brake LightsComponent Location fndex ...................21-3 Altemator CircuitDiagram....................................22-74Description.....................................-....21'1'l Beplacement ................ ........................... 4 29CircuitDiagram....................................21-14 Overhaul .................................................4-30 Brake Lines and Hoses
19.10
A/C CompressolReplacement .......-...-............................. 21 -41
A/C Compr€ssor ClulchRep1acement......................................... 19-15.........22-103 Inspection ............................................. 19-16Inspecton........Overhaul ..........
A/C CondenserReplacement,.,
21-442l-49 Audio Unit
Replacement
Brake PadsRemoval/lnstallation .. ........................22-100 Inspection/Rep1acement................ 19-11,20A/C Compressor Clutch CircuitTroubleshooting ................................... 21-30 Audio Unit Connector Brake Pedal22101 Adjustment..............19,6ArfC Comoressor Relief ValvcReplacement ..........-...-.......................... 21-51 Audio/Entertainment
A/C Compr$sor Thermal Protector Circuit DiagramReplacement............-............................ 21-51
Component Location In dex .................22-9A Test .......-.............. 22-84Breke Pedal Posilion Switch
Brake Pedal Position Switch Signal Clrcuit11-137
.....21 52
A/C Condenser Fan CircuitTroubleshooting ................... . . . . . .....21-28
)s
Troubleshooting
(cont'd)

)
Orive BehInspecaron................ 4-26
Door PanelsRemoval/lnstallation -............................. 20-4
Door Sash TrimRep1acement......................................... 20 10
Door StrikersAdiustment ........................................... 20-13
Door Weatherst psBeplacement...........-............................. 20 1 1
EPS Conirol UnitRemoval/1nsta11ation ..................-......... 17-67
EPS Indicator CircuitTroubleshooting ................................... 17 -47
EPS MotorRemoval/lnstallation .-.......................... 17-49
EVAP CanisterRep1acement......................... ......... 11,189
EVAP Control Syst€mComponentLocation Index ..............'11-170
EVAP Two-Wey ValveTest ..........-.............-............................ 11 186
Evaporetor CoreRep1acement........................ . ... 21-42
Evaporator Tomperature SensorReplacement......................................... 21 -37Test..................................... ..........2137
EvaporrtoFHeater UnitReplacement........................................ 21 43
Exhaust ManifoldRemoval/1nsta11ation ................................ I 7
Exhaust Pipe8ep|acement............................................. 9-8
Front SpeakersRep|acement....................................... 22-102
Front SuspensionComponentLocation Index................... 18-3
Fueland EmissionsDescription ........................................... 11-12
Fuel Fill DoorAdjustment ..........-................................ 20 93
Fuel Fill Door OpenetBeplacement........................ . ............ 20.109
Fuel Fill Door Opener CableReplacement....................................... 20- lO7
Fuel FilterReplacement....................................... 1 1-152
Fuel Gauge Sending UnitTest ......................-.-..........-.................. 11'156
Fuel Injection Syslem (PGM"FIlComponent Location 1ndex................. 11-49
Fuel IniectorsRep1acemen1....................................... 1 1 1 1 l
Fuel Lines and HosesInspection .......................................... 1 1'146Removal ....................... . .. . .... 11-149Insta|1ation .......................................... 1 1 150
FuelPipe ProtectolReplacement....................................... 20-104
Fuel Pressure RegulatotReplacement....................................... 1 1-152
Fuel Pulsation DamperReplacemenl................................... 11 154
Fuel PumpReplacement,,,,,.,.,.,,,.,,,,,,,,,,,,.,.,.,,,..,.. 11-153
Fuel Pump CircuitTroubleshooting -.......-....................... 1 1-141
FuelSupply SystemComponent Location lndex .............. 11 140Adjustment................................... 11-144Test........-...-................. ... ............- 11-145
FuelTankBeplacemenl.............. . ..... .. 11 155
Fuel Tank Vapor ControlValveTest ......................-....... ... . . 11-187Replacement,,.,,...,.,,,.,.,,,,... .. .. 11 189
Fuses{See first page ofthis Index)
)
Rep|acement................. ..................... 4 26
Drive Belt Auto-tensionellnspection ............................................... 4 21Rep1acement.................................... ..4-28
Driver's PocketRemoval/lnstallation -........................... 20-60
Driver's TrayRemoval/lnstallation .........................-.- 20-65
DRL {Daytime Running LightslControl Unitlnput Test .................... ........ . . . ......22-16
DTCs(See first page olthis Index)
Dust and Pollen FillerReplacement......................................... 21-39
Dynamic Damper, DriveshaftsReplacement........................................... 16-8
ECT SensorReplacement.,.,,,.,.,,,,,,,,,,,,,,................ 1 1-1 14
El€ctrical Power Steering IEPS)Signal CircuitTroubleshooting ........ ... .. 11-135
EmblemsReplacement......................-................ 20-100
Engine AssemblyRemova1 .................................................... 5 2Installation ............._.................................. 5-9
Engine Block AssemblyComponent Location Inder ..................... 7.3
Engine Block, BareInspect|onRepair
Fan ControlsComponent Location Index................. 10'l 1Circuit Diagram .. ..... . .. . .................. 10 13
Fender Fairing, FrontReplacement...-................................... 20-103
Final Driven Gear. M/TReplacement.... . . ................................ 13-53
FrameRepair Chan............ ... ....................... 20 11 4
Frame StiffenelReplacement......-................................ 20- J'13
Front ConsoleRemoval/lnstallation ............................ 20 5lDisassembJy/Reassemb|y ................... 20 58
Front DoorsComponent Location Index................... 20-2Adiustment ........................................... 20.12
Front Driveshaft AssemblyInspeclion .................... ... ....16 3Remova1...................-...... ... .....16-3Disassembly ............................... .....165Resassemb|y ................................-......... 16-9Insta11arion ........................ ...... ............ l6 17
Front lmpact SensorsRep1acement............................ ...23 125
................7-15................1 11
)
Entry Light Control SystemComponent Location Index ...............-. 22-89Circuit Dia9ram .................................... 22 90
EPS ComponentsComponent Location 1ndex..........-...... 17-!7Description ........................ ...... ..17-24Circuit Diagram11 26(cont'd)

Service Manual lndex
(cont'dl
Power Window Switch, Passenger'slnput Test .............-......
Replacement...,-.-.-...,..
Radialor Cap
Rocker Arm AssemblyRemovalD;sassembly/Reassembly
Specifications6-26 (See section 2)22-13022 13222-133..................... 6-27
ComponentLocation Index ..............22 124Circuit Dia9ram .................. ............... 22 125
Ouaner Window Glass8ep1acement ......................................... 20-29
lnstallation6-38
Rocker ArmsTestInspecton6-28
Roof MoldingsReplacement
Seat BeltsComponent Location Index ................... 23-3
Seat 8ehs, FrontReplacementrnspec!on
sRsComponent Location Index ................. 23-13Description ....................................... 23-31Circuit D;agram ... .... ...........2334lnspection/Replacemenl ................... 23 1 126-7
SRS lndicator CircuilTroubleshooting
Startel
Stabilizer BarReplacementFront SuspensionRear Suspension
Stabilizer LinksRemoval/lnstallationFront SuspensionRear Suspension
23 105oSRS UnitReplacement..-.................................... 23-122s
R
1A-1718-30
18 1818-31RadiatorTest......23-9
23-1Replacement ...........
Radiator and Condenser FansCommon CircuitTroubleshooling......... ..... .........21 29
10-310-10Seat Behs, RearReplacement
Seat Cover, FrontReplacement
Seat Cushion Cover, R6ar10-3Replacement
ReplacementTest
Test
20-75
20-84
Overhaul
Starter SolenoidTest..-.-...4-7
Radiator Fan AssemblyTestSeat, Driver'sRemovaf/lnstaf lation ............................ 20 1 1Disassembly/Reassemb1y ................... 20-73
Sedt, Faont Passenger'sDisassembly/Reassemb1y ................... 20-74
Seat, RearRemoval/lnstallation ............................ 20-80
Seat-back Cover, Reer
Starting SystemComponent Location Index...............-..... 4-3CircuitDia9ram ........................................ 4 4
\'{........................ r0-4
Radiator Fan CircuitTroubleshooting
Radiator Fan SwhchReplacementTest
Radiator Fan Switch CircuitTroubleshooting
Rear Air OutletReplacement
Circuil DiagramTest
Rear Window D€rogger WiresRepair
RearWindow GlassReplacement
Troubleshooting10-14
10-1710-17
10 16
17 -3
11-4
17-9
SteeringComponent Location Index................-..Inspectaon ...................
Steering ColumnRemoval/lnstallationReplacementInspection11 11
17-5117 5517 63
20 68
Seat-back Latch, ReaI2Q-104Replacement
Seat-back Striker. RearReplacement
Steering GearboxRemovalOverhaulRear Window DefoggerComponentLocalion Index ..............22 104lnstallation
Steering Hanger BeamReplacement
Steering LinkageInspefiron
Steering LockReplacement
Steering Rack GuideAdiustment
22-10522 106
22-106
SeatsComponent Location Index....-............ 20-70
Shift ForksInspectton13,21
20-25
2l-3621 36
21 25
Disassembly/Reassembly ................... 13-22
Shitt Lever TrimRemoval/lnstallation ............................ 20 61
.....11-12
SecirculationReplacementControl Motor17-13Test.....
Recirculation Control Motor CircuitTroubleshooting
Side Airbag, Drivel'sReplacement
Side lmpact SensorsReplacement
Spark Plugs
23-115
23 123
Side Marker LightRep1acement......................................... 22-A3
17417-6Disassembly/Reassembly ..................... 17 71nsta11ation .............................................. 17-8
SublramesReplacement
Removal
RefrigerantReplacement ..-.-.-...................... 21 53, 54, 55Test ........................................................ 21-56
Retrigerant OilReplacement...............................-........... 21-6. .._..4_19
20 112