2003 HONDA CIVIC HEATER UNIT

Heater Unit/Core Replacement
SRS components are located in this area. Review the
SRS component locations (see page 23'13), and
precautions and procedures (see page 23-14) in the SRS
section before performing repairs or service.
1. Make sure you have the anti-theft code forthe radio,
then write down the freouencies for the radio's
Dreset buttons.
4.
Disconnect the negative cable from the battery,
Disconnect the suction and receiver lines from the
evaporator core (see page 21-42).
From under the hood, open the cable clamp (A),
then disconnect the heater valve cable (B) from the
heater valve arm (C). Turn the heater valve arm to
the fully opened position as shown
When the engine is cool, drain the engine coolant
from the radiator (see page 10-6).
6. Slide the hose clamps (A) back, the n d isconnect the
inlet heater hose (B) and the outlet heater hose (C)
from the heater core. Engine coolant will run out
when the hoses are disconnected; drain it into a
clean drip pan. Be sure not to let coolant spill on
the electrical parts or the painted surfaces. lf any
coolant spills, rinse it off immediately.
Remove the bolt and the heater valve, then remove
the mounting nut from the heater unit. Take care
not to damage or bend the fuel lines and the brake
lines, etc.
7.
8 x 1.25 mm12 N.m (1.2 kgf.m,8.7lbf.ft)
(cont'd)
21-43

Heating and Air Conditioning
Heater Unit/Core Replacement (cont'd)
8. Remove the dashboard {see page 20-66).
9. Disconnectthe connectors (A) from the blower
motor, the recirculation control motor, the mode
control motor, and the power transistor, then
remove the wire harness clips (B) and the
connector (C). Remove the self-tapping screws and
the bracket (D).
Disconnect the connectors (A) from the evaporator
temperature sensor and the air mix control motor,
then remove the wire harness clips (B) and the
connector (C). Remove the self-tapping screw and
the cover (D). Disconnect the heater valve cable (E).
10,
7t,
21-44
11. Remove the mounting bolts, the mounting nuts,
and the heater unit.
Remove the self-tapping screws and the expansion
valve cover (A). Carefully pull out the evaporator
core (B) so you don't bend the inlet and outlet pipes.
Remove the grommet (C), then remove the self-
tapping screws and the flange cover (D). Bemove
the self-tapping screws and the pipe cover (E), then
carefully pull out the heater core (F) so you don't
bend the inlet and outlet oioes.
@
5x 1.0 mm9.8 N.m11.0 kgl m,7.2 tbf.ftl
12.

13. Installthe heater core and the evaporator core in
the reverse order of removal.
14. Installthe heater unit in the reverse order of
removal, and note these items:
. Do not interchange the inlet and outlet heater
hoses, and installthe hose clamps securely.. Refillthe cooling system with engine coolant (see
page 10-6).. Adjust the heater valve cable (see page 2'l-461.. Make sure that there is no coolant leakage.. Make sure that there is no air leakage.. Refer to evaporator core replacement {see step 6
on page 21-42).. Do the engine control module (ECl\4) idle learn
procedure (see page 11-139).. Enter the anti-theft code for the radio, then enter
the customer's radio station Dresets.
21-45

Connectors and Harnesses
Dashboard Wire Harness A {Left branchl
Connector or TerminalffiAccessory power socketAudio antennaBrake pedal position switchClutch interlock switchClutch pedal poistion switchCruise control unitCruise main switchDaytime r!nning lights control unitDaytime running lights relayGauge assembly connector AGauge assembly connector BHazard warning switchHeater control panel connector AHeater control panel connector BHVAC push switch assemblyKeyless receiver unitLow beam cut relayOptional security connectorPower mirror switchUnder-dash fuse/relay boxconnector K (see page 22-45)Under'dash fuse/relay box
L {see page 22-45}Underdash fuse/relay boxconnector M lsee page 22'45)Under-dash fuse/relay boxconnector N (see page 22-45)UndeFdash fuse/relay boxconnector O (see page 22-45)UndeFdash fuse/relay boxconnectorY (see page 22 45)c504
c505
c506
c507
c508
c509
c510
22226
3029628
I820111819105327
,I4
12
11
34
1
24
25
2 Under middle of dash2 Under left side of dash4 ] Under left side of dash2 ] Under left srde of dash2 | Under left side of dash14 I Under left side of dash5 Under left side of dash14 Under lett side of dash4 Under lett side of dash22 I Behind gauge assembly22 i Behind gauge assembly10 Behind hazard warnning switch22 Behind heater control panel'14 Behind heater control panel10 ] Behind HVAC switch assembly5 I Under middle of dash5 lUnderleftsideofdash16 Under lefr side of dash13 Under left side oI dash17 ln the under-dash fuse/relay box
CanadaCanada
l0In the under-dash fuse/relay box
In the undeFdash fuse/relay box
In the underdash fuse/relay box
In the under-dash fuse/relay box
In the under-dash fuse/relay box
Under left side of dash
Under left side ot dash
Under left side of dash
Under left side of dash
Under middle of dash
Under middle of dash
Under middle ol dash
Driver's door wire harness(see page 22'40)Driver's door wire harness(see page 22-40)Left side turo signal lightsuonarnessRoof wire harness (see page22 3AlFloor wire harness {see page22-341Floor wire harness (see page22 34JDashboard wire harness B(see oaoe 22-30)
12
12
G501
G503
1
21
Under gauge assembly
Under left side of dash
Body ground via dashboard
Body ground via dashboard
Left Side Turn Signal Light Sub harness
Connector to Harness Index (cont'd)
L
Connector or TerminalCavitiesLocationConnects toNolesLeft side turn signal lightc506353422Behind left side turn signal lightUnder left side of dashDashboard wire harness A
22-26

Under-dash Fuse/Relay Box
Fuse
Number
AmpsWire ColorComponent(s) or Circuit(s) Protected
115ABLKA/VHTlgnition coils
2204WHT/REDAirlfuel ratio sensor, ECM
310ARED/BLUDaytime running Iights control unit {Canada)10ABLI(ORNAir/fuel ratio sensor relay, Alternator, CMP sensor, Cruise control main
switch, Cruise control unit. ELD unit, Evaporative emission (EVAP) bypass
solenoid valve, Evaporative emission (EVAP)canister purge valve,
Evaporative emission (EVAP) canister vent shut valve, Secondary H02S,
Vehicle speed sensor
5Not used
67.5AYEUGRNMoonroof control unit, Moonroof open and close relay, Power window
relaV
7204GRNMoonroof motor
I7.5AYEUREDAudio unit
910AGRNOPDS unit, Rear window wiper motor, Rear window washer motor, Rear
window wiper intermittent control unit
107.54YELBack-up lights, Cruise indicator light, EPS control unit, Gauge assembly,
Keyless receiver unit, Multiplex control unit, Security control unit
connector (optional)
117.5ABLIVORNABS modulator-control unit
127.5AYEUREDDaytime runnino liohts control unit (Canada)
1310APNKSRS unit't410ABLK/YE LA,,/C compressor clutch relay, Blower motor relay, Condenser fan relay,
Heater control panel, Power mirror actuator, Power mirror defogger(Canada), Radiator fan relay, Rear window defogger relay, Recirculation
control motor1ENot used
loNot used
1715AYE L/B LKECM, Fuel pump
B LK/YE L>H> Unrr
1815AYEUGRNAccessory power socket
197.5AYEUBLKTurn siqnal/hazard relav, Turn siqnal liohts
2030AGRN/BLKMultiplex control unit, Windshield washer motor. Windshield wioer motor21Not used
22204GRN/BLKPassenqer's window motor
2320A.G R N,A/VHTDriver's window motor
24Not used
25Not used
__^:Hr tl_l
f at-t
at I
r^,rl fl
!!;r -
!339,i;s!!sf Fnf : |rnITf
22-47

Ground Distribution
Ground to Components Index
GroundComponent or circuit qrounded
Batterv, Transmission housinq
E ngine
G 101ECM (PG is BLK; LG is BRN/YEL)
BLK: IAC valve, lgnition coils, Vehicle speed sensor, VTEC solenoid valve
BRNA/EL: Camshaft oosition (CMP) sensor. CKP sensor, TDC sensor. VTEC oil pressure switch
G 15']EPS control unit
G201ELD unit. Multiplex control inspection connector, Multiplex control unit, Power window relay, Rear
window washer motor, Right front parking light, Right front side marker light, Right front turn signal
light, Turn signal/hazard relay, Washer fluid level sensor (Canada) , Windshield washer motor,
Windshield wiDer motor
G202ABS modulator-control unit
G301
G401
Blower motor relay, Brake fluid level switch, Condensor fan motor, Cruise control actuator, Left front
parking light, Left front side marker light, Left front turn signal light, Radiator fan motor, Radiator fan
swrtcn
Combination liqht switch, lqnitlon kev srvitch, Wiper/wasfrer sr,virch
G402Left and riqht airbaq sensors, SRS unit
G 451Data link connector (DLC)
G501Clutch interlock switchm Clutch pedal position switch (for cruise control), Cruise control main switch,
Cruise control unit, Daytime running lights control unit (Canada), Driver's door lock knob switch,
Driver's door lock switch, Driver's power window motor, Heater control panel, Left power mirror
defogger (Canada), left side turn signal light, Moonroof control unit, Monroof open and close relays,
Moonroof position sensor '1, Moonroof seitch, Power mirror switch, Power transistor, Power window
master switch. SDotliqhts
G502Accessory power socket, Gauge assembly, Keyless receiver unit, lvlultiplex control unit, Right power
mirror defogger {Canada)
G503Audio unit
G551Driver's seat belt switch, Fuel gauge sending unit, Fuel pump, Memory erase signal (IMES) connector,
OPDS unit. Rioht seat belt switch
G552High mount brake light, License plate lights, Rear window defogger, Rear window defogger noise
condenser. Rear window wioer motor, Hatch latch switch
Back-up lights, Brake lights, Rear side marker lights, Rear turn signal lights, Rear window wiper noise
condenser, Rear window wiper intermittent control unit, Taillights
22-48

Audio System
Audio Unit Removal/lnstallation
NOTE:. Put on gloves to protect your hands.. Take care not to scratch the dashboard and relatedpa rts.
1. Make sure you have the anti-theft code for the radio,
then write down the frequencies for the radio's
preset buttons.
2. Remove the driver's dashboard lower cover (see
page 20-59).
3. Remove the two mounting bolts, then pull out the
center panel (A).
4.Disconnect the audio connector (B) and antenna
lead (C), heater control panel connectors (D) and
HAVC push switch assembly (E), then remove the
center panel.
22-100
!\,
7.
Remove the heater control panel (see page 21 38).
Remove the four mounting bolts and the audio unit
from the radio brackets.
Installthe audio unit in the reverse order of
removal, and note these items:
. Make sure the audio unit and A/C connectors areplugged in properly, and the antenna lead is
connected properly.. Enter the anti-theft code for the radio, then enter
the customer's radio station presets.
\v
I

)
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)