2003 HONDA CIVIC Circuit

Multiplex Control System
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Circuit Diagram (cont'd)
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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.

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Restraints
Restraints
Special Tools ............. 23-2
Seat Belts
Component Location Index ......................................... 23-3
Front Seat Belt Replacement ....................................... 23-4
Rear Seat Belt Replacement ........................................ 23-6
Inspection .................. 23-8
Child Seat Tether Anchor Removal/lnstallation ........ 23-9
SRS (Supplemental Restraint Systeml
Component Location Index ......................................... 23-13
Precautions and Procedures ,,.,......... 23-14
General Troubleshooting Information ....................... 23-23
DTC Troubleshooting Index .............. 23-28
Symptom Troubleshooting Index ............................... 23-30
System Description ................. ........... 23-31
Circuit Diagram ......... 23-34
DTC Troubleshooting ............... .......... 23-36
SRS Indicator Circuit Troubleshooting ....................... 23-105
Component R e place me n(/ln s pect io n After
Deployment ..............23-112
Driver's Airbag Replacement ............ 23-113
Front Passenger's Airbag Replacement ..................... 23-1 14
Side Airbag Replacement .................. 23-115
Airbag Disposal ....................... ........... 23-116
Cable Reel Replacement .................... 23-119
SRS Unit Repfacement ....................... 23-122
Side fmpact Sensor Replacement ..........,.................... 23-123
OPDS Unit Replacement .................... 23-124
Front fmpact Sensor Replacement .............................. 23-125

sRs
Precautions and Procedures
General Precautions
Please read the following precautions carefully beforeperforming airbag system service. Observe theinstructions described in this manual. or the airbags
could accidentally deploy and cause damage or injuries.
. Except when performing electrical inspections.
always turn the ignition switch OFF, disconnect the
negative cable from the battery, and wait at least 3minutes before beginning work.
NOTE: The memory is not erased even if the ignition
switch is turned OFF or the battery cables are
disconnected from the battery.. Use replacement pans which are manufactured to the
same standards and quality as the original parts. Do
not install used SRS parts from another vehicle. Useonly new pans when making SRS repairs.. Carefully inspect any SRS part before you install it.
Do not install any part that shows signs of being
dropped or improperly handled, such as dents, cracks,
or deformation.
. Before removing any SRS parts (including the
disconnection of connectors), always disconnect the
SRS connector.. Use only a digital multimeter to check the system. lf itis not a Honda multimeter, make sure its outout is 10mA (0.01A) or less when switched to the lowest value
in the ohmmeter range. A tester with a higher output
could cause accidental deployment and possible
injury.. Do not put objects on the front passenger's airbag.. The original radio has a coded theft protection circuit.
Be sure to get the customer's radio code and write
down the frequencies for the radio's preset stations
before disconnecting the battery cable.. Before returning the vehicle to the customer, enter
the radio code. then enter the customer's radio
station presets, and set the clock. Do the engine
control module (ECM) idle learn procedure (see page
11-139).
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Steering-related Plecautions
Cable Reel Alignment
. Misalignment of the cable reel could cause an open in
the wiring, making the SRS system and the horns
inoperative. Center the cable reel whenever the
following is performed (see step 6 on page 23-121).
- Installation of the steering wheel- Installation of the cable reel- Installation ofthe steering column- Other steering-related adjustment or installation
. Do not disassemble the cable reel.
. Do not apply grease to the cable reel.
. lf the cable reel shows any signs of damage or
contamination. replace it with a new one. For
example, it does not rotate smoothly.

General Troubleshooting Information
DTC (Diagnostic Trouble Codesl
The self-diagnostic function of the SRS system allows it
to locate the causes of system problems and then store
this information in memory. For easier troubleshooting,
this data can be retrieved via a data link circuit.
. When you turn the ignition switch ON (ll), the SRS
indicator will come on. lf it goes off after 6 seconds,
the system is normal.. lf there is an abnormality, the svstem locates and
defines the problem, stores this information in
memory, and turns the SRS indicator on. The data
will remain in the memory even when the ignition
switch is turned off or if the battery is disconnected.. When you connect the Honda PG lM Tester to the 16P
data link connector (DLC)to short the SCS terminal,
and turn the ignition switch ON (ll). the SRS indicator
will indicate the diagnostic trouble code (DTC) by the
number of blinks.. When you connect the Honda PGM Tester to the 16P
data link Connector (DLC), you can retrieve the DTC in
the Honda Systems "SRS" menu.. After reading and recording the DTC, proceed with
the troubleshooting procedure for th is code.
Precautions. Use only a digital multimeter to check the system. lf
it's not a Honda multimeter, make sure its output is
10 mA (0.01A) or less when switched to the smallest
value in the ohmmeter range, A tester with a higher
output could damage the airbag circuit or cause
accidental airbag deployment and possible injury.. Whenever the ignition switch is ON (ll), or has been
turned OFF for less than 3 minutes, be careful not to
bump the SRS uniU the airbags could accidentally
deploy and cause damage or injuries.. Before you remove the SRS harness, disconnect the
driver's airbag connector. the front passenger's
airbag connector, both side airbag connectors, both
seat belt buckle tensioner connectors, and both seat
belt tensioner connectors.. Make sure the battery is sufficiently charged. lf the
battery is dead or low, measuring values won't be
correct.. Do not touch a tester probe to the terminals in the
SRS unit or harness connectors, and do not connect
the terminals with a jumper wire. Use only the
backprobe set and the Honda PGM Tester. Backprobe
spring loaded lock type connectors correctly.
Reading the DTC
When the SRS indicator is on, read the DTC using either
of the following methods:
PGM Tester "SRS" Menu Method:
Connect the Honda PGM Tester {A) to the 16P data link
connector {DLC)(B), and follow the Tester's Drompts in
the "SRS" menu.
lf the Tester indicates no DTC, no communication. DTC
3-6 to 3-'10, DTC 4-6 to 4-10, DTC 9-1, or DTC 9-2,
double-check by using the "SCS" menu method.
(cont'd)
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Including the most recent problem, up to three different DTCS can be indicated (see example 1 below).ln case of a continuous failure, the DTC will be indicated repeatedly {see example 1 below).In case of an intermittent failure, the SRS indicator will indicate the DTCS one time, then it will stay on (see example2 below).
lf both a continuous and an intermittent failure occur, both DTCS will be indicated as continuous failures.When the system is normal (no DTCS), the SRS indicator will stay on (see example 3).lf the SRS indicator comes on continuously without a DTC, there mav be a problem with the svstem.lf the SRS indicator does not come on as indicated above, always check for an open or a short to ground in the SCScircuit before troubleshooting the system.
Example of DTC Indications:
1. Continuous failure, SRS Indic6tor blink$ like this:
1.2 S 1,2 SS: Second0.3s 0.3s
ON
OFF
Bulb checkperiodMain code (21 Subcode l1)
DTC 2-lMost recent p.oblem
2. Intermittent failure, SRS lndicator blinks like this:ON
Main code l1lSubcode (3) Main code {11 Subcode {'l)Indicationsare lepeatedtn cese otcontinuousfailure.
lndicator stays on incase of i nterm ittent failu re.
(cont'd)
DTC 1-3DTC 1-1Sscond-mostrecent Third-mostrocentproblem problem
OFF
Bulb checkperiodDTC 5-1
3. Normal (no failure|, SRS Indicator blinks like this:ON
OFF
Bulb chockperiodNo DTC, systom is normal, the indicatorstays on.
0.3 s
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DTCDetection ltemNotes9-1Internal failure of the SRS unit. lf intermittent, it could mean internalfailure of the unit or a faulty indicator circuit. Refer toTroubleshooting Intermittent Failures (see page 23-26).
NOTE: Before troubleshooting DTC 9-1 or 9-2, check battery/systemvoltage. lf the voltage is low, repair the charging system beforetroubleshooting the SRS.
(see page 23-69)
9-2Internal failure of the SRS unit. lf intermittent, it could mean internalfailu re of the power supply (VB line). Refer to TroubleshootingIntermittent Failures (see page 23-26).
NOTE: Before troubleshooting DTC 9-1 or 9-2, check battery/systemvoltage. lf the voltage is low, repair the charging system or replacethe b€ttery before troubleshooting the SRS.
9-3Faulty driver's seat belt buckle switch(see Daqe 23-71)9-4
9-6
FaultLtglt passenger's seat belt buckle switch
Faulty Ieft front imDact sensorlgqgfage 23-74)
{see Daqe 23-77)9-7Faulty right front impact sensor(see paqe 23-79)10-1Seat belt and seat belt buckle tensioners (and airbag(s)) deployedDriver's side airbag deployed
Seat belt and seat belt buckle tensioners (and airbag(s)) and driver'sside airbag deployed
Front passenqer's side airbao deDloved
(see page 23-69)10-2
r0-3
'10-4
'10-5Seat belt and seat belt buckle tensioners (and airbag(s)) and frontpassenqer's side airbaq deDloved
10-6Driver's and front passenqer's side al10-7Seat belt and seat belt buckle tensioners (and airbag(s)) and driver'sand front passenger's side airbags deployed
1 1-1Open or increased resistance in driver's side airbao inflator(see paqe 23-81)Short to another wire or decreased resistance in driver's side airbaoinflator
(see page 23-82)
11-4Short to power in driver's side airbaq inflator(see oaqe 23-83)I t-5Short to ground in driver's side airbaq inflator{see paqe 23-85)Open or increased resistance in front passenger's side airbaginflator
(see page 23-86)
Short to another wire or decreased resistance in front passenger's
side airbag inflator
(see page 23-87)
12-4Short to power in front passenqer's side airbaq inflator{see Daqe zJ-uu}I z-5Short to ground in front passenger's side airbaq inflator(see oaqe 23-90)13-1Internal failure of the driver's side impact sensor(see page 23-70)
No signal from the driver's side impact sensor(see paqe 23-91)13-4
14-1-7ii,
Faulty power supply to the df,rglllug t Opact s9I99LInternal failure ofthe front passenger's side impact sensor
(see page 23-92)(see page 23-70)
14-3No signal from the front passenger's side impact sensor(see paqe 23-94)14-4Faulty power supply to the front passenqer's side impact sensor(see page 23-95)15-1Faultv OPDS unit or OPDS not initialized(see paqe 23-96115-2Faulty side airbag cutoff indicator circuit(see Daqe 23-99)15-3Faulty OPDS sensor(see oaoe 23-104)
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sRs
System Description (cont'dl
SRS Operation
The main circuit in the SRS unit senses and judges the force of impact and, if necessary. ignites the inflator charges. lf
battery voltage is too low or power is disconnected due to the impact, the voltage regulator and the back-up power
circuit, respectively, will keep voltage at a constant level.
For the SRS to operate:
Seat Belt Tensioners and Seat Belt Buckle Tensioners
(1) A front impact sensor must activate and send electric signals to the microprocessor.
(2) The microprocessor must compute the signals and send them to the tensioners.
(3) The charges must ignite and deploy the tensioners.
Driver's and Front Passenger's Airbagls)
(1) A front impact sensor musl activate. and send electric signals to the microprocessor.
(2) The microprocessor must compute the signals. and depending on the severity of the collision and whether the seat
belt buckle swilch is ON or OFF, it sends the appropriate signals to the airbag inflator(s).
(3) The inflators that received signals must ignite and deploy the airbags.
Side Airbaglsl( 1) A side impact sensor must activate, and send electric signals to the microprocessor.
(2) The microprocessor must compute the signals and send them to the side airbag inflator(s). However, the
microprocessor cuts off the signals to the front passenger's side airbag if the OPDS unit determines that the tront
passenger's head is in the deployment path of the side airbag.
(3) The inflator that received the signal must ignite and deploy the side airbag.
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