Isuzu KB P190. Manual - part 1413

SUPPLEMENTAL RESTRAINT SYSTEM  9A-17 

“Continuous Monitoring” 
Tests are performed by the SRS control unit on the
SRS every 100 milliseconds while “Ignition 1” voltage
is in the normal operating voltage range at the SRS
control unit. 

Data Link Connector (DLC) 
Formerly “DLC”, a connector which allows
communication with an external computer, such as a
scan tool. 

Datum Line 
A base line parallel to the plane of the underbody or
frame from which all vertical measurements originate.

Deploy 
To inflate the air bag. 

Deployment Loops 
The circuits which supply current to the air bag
assemblies to deploy the air bag. 

Diagnostic Trouble Code (DTC) 
Formerly “Code”, a numerical designator used by the
SRS control unit to indicate specific SRS malfunctions. 

Driver Current Source 
An output of the SRS control unit which applies current
into the driver air bag assembly circuit during the
“Initiator Assembly Resistance Test”. 

Driver Air Bag Assembly 
An assembly located in the steering wheel hub
consisting of an inflatable bag, an inflator and an
initiator. 

EEPROM 
Electrically Erasable Programmable Read Only
Memory.  Memory which retains its contents when
power is removed from the SRS control unit. 

Ignition Cycle 
The voltage at the SRS control unit “Ignition 1” input,
with ignition switch “ON”, is within the normal operating
voltage range for at least ten seconds before turning
the ignition switch “OFF”. 

Ignition 1 
A battery voltage (B+) circuit which is only powered
when the ignition switch is in the ON, or START
position. 

Initiator 
The electrical component inside the air bag assembly
which, when sufficient current flows, sets off the
chemical reaction that inflates the air bag. 

 

 

“Initiator Assembly Resistance Test” 
Tests are performed once for each ignition cycle when 
no malfunctions are detected during “Turn–ON” or 
“Continuous Monitoring”. This test checks for the 
correct SRS control unit configuration for the vehicle, 
shorts to “Ignition 1” in the deployment loops, high 
resistance or opens in the “Driver Side” and 
“Passenger Side” circuits and measures the resistance 
of the inflator assembly consisting of 1) Initiators, 2) 
SRS coil assembly (driver side only), 3) Connectors 
and associated wiring. 

Normal Operating Voltage Range 
The voltage measured between the SRS control unit 
“Ignition 1” terminals and “Ground” terminals is 
between 9 and 16 volts. 

Passenger Current Source 
An output of the SRS control unit which applies current 
into the passenger air bag assembly circuit during the 
“Initiator Assembly Resistance Test”. 

Passenger Air Bag Assembly 
An assembly located in the front of the passenger side 
of the instrument panel consisting of an inflatable bag, 
an inflator and an initiator. 

Scan Tool 
An external computer used to read diagnostic 
information from on–board computers via the data link 
connector. 

SRS control unit 
SRS control unit which provides reserve energy to the 
deployment loops, deploys the air bags when required 
and performs diagnostic monitoring of all SRS 
components. 

Serial Data 
Information representing the status of the SRS. 

SRS 
Supplemental Restraint System. 

SRS Coil Assembly 
An assembly of two current–carrying coils in the driver 
deployment loop that allows the rotation of the steering
wheel while maintaining the continuous contact of the 
driver deployment loop to the driver air bag assembly.

SRS Wiring Harness 
The wires and connectors that electrically connect the 
components in the SRS. 

“Turn–ON” 
Test which the SRS control unit performs on the SRS 
once during each ignition cycle immediately after 
“Ignition 1” voltage is applied to the SRS control unit 
and before “Continuous Monitoring”. 

 

9A-18  SUPPLEMENTAL RESTRAINT SYSTEM 

Diagnosis 

WARNING: TO AVOID DEPLOYMENT WHEN
TROUBLESHOOTING THE SRS, DO NOT USE
ELECTRICAL TEST EQUIPMENT SUCH AS A
BATTERY–POWERED OR AC–POWERED
VOLTMETER, OHMMETER, ETC., OR ANY TYPE
OF ELECTRICAL EQUIPMENT OTHER THAN THAT
SPECIFIED IN THIS MANUAL.  DO NOT USE A
NON-POWERED PROBE–TYPE TESTER.
INSTRUCTIONS IN THIS MANUAL MUST BE
FOLLOWED CAREFULLY, OTHERWISE
PERSONAL INJURY MAY RESULT. 

Diagnostic Trouble Codes 

The “SRS Diagnostic System Check” must always be
the starting point of any SRS diagnosis.  The “SRS
Diagnostic System Check” checks for proper “SRS”
warning lamp operation and checks for SRS
diagnostic trouble codes using the scan tool. 

 1. Current diagnostic trouble codes – Malfunctions

that are presently being detected.  Current
diagnostic trouble codes are stored in RAM
(Random Access Memory). 

  2. History diagnostic trouble codes – All malfunctions 

detected since the last time the history memory
was cleared.  History diagnostic trouble codes are
stored in EEPROM. 

 

 

Scan Tool Diagnostics 

A scan tool is used to read current and history 
diagnostic trouble codes and to clear all diagnostic 
trouble codes after a repair is completed.  The scan 
tool must be updated to communicate with the SRS 
through a replaceable cartridge before it can be used 
for SRS diagnostics.  To use the scan tool, connect it 
to the data link connector and turn the ignition switch 
“ON”. The scan tool reads serial data from the SRS 
control unit “Serial Data” line terminal “21” to the data 
link connector terminal “2”. 

 

Use Of Special Tools 

WARNING: TO AVOID DEPLOYMENT WHEN 
TROUBLESHOOTING THE SRS, DO NOT USE 
ELECTRICAL TEST EQUIPMENT SUCH AS A 
BATTERY–POWERED OR AC–POWERED 
VOLTMETER, OHMMETER, ETC, OR ANY TYPE OF 
ELECTRICAL EQUIPMENT OTHER THAN THAT 
SPECIFIED IN THIS MANUAL.  DO NOT USE A 
NON-POWERED PROBE–TYPE TESTER. 
INSTRUCTIONS IN THIS MANUAL MUST BE 
FOLLOWED CAREFULLY, OTHERWISE 
PERSONAL INJURY MAY RESULT.  YOU SHOULD 
BE FAMILIAR WITH THE TOOLS LISTED IN THIS 
SECTION UNDER THE HANDLING SRS SPECIAL 
TOOLS. 

You should be able to measure voltage and 
resistance.  You should be familiar with proper use of 
a scan tool such as the Tech 2 Diagnostic Computer, 
SRS Driver/Passenger Load Tool 5-8840-2421-0, 
Connector Test Adapter Kit 5-8840-2835-0 and the 
DMM (Digital Multimeter) 5-8840-0366-0. 

 

 

SUPPLEMENTAL RESTRAINT SYSTEM  9A-19 

SRS Connector Body Face Views 

  

 

 

 

RTW79AMF000201 

Legend 

  (1) SRS control unit 

  (2) Driver Air Bag Assembly 

  (3) Passenger Air Bag Assembly 

 

 

  (4) “SRS” Warning Lamp 

 (5) 

DLC 

 

 

 

9A-20  SUPPLEMENTAL RESTRAINT SYSTEM 

Repairs And Inspections Required 

After An Accident 

If any SRS components are damaged, they must be
replaced.  If SRS component mounting points are
damaged, they must be replaced. 

•  Never use SRS parts from another vehicle.  This

does not include remanufactured parts purchased
from an authorized dealer; they may be used for
SRS repairs. 

•  Do not attempt to service the SRS control unit, the

SRS coil assembly, or the air bag assembly.
Service of these items is by replacement only. 

•  Verify the part number of the replacement air bag

assembly. 

 

CAUTION: Never use the air bag assembly from
another vehicle or different model year air bag
assembly. 

Use only a new air bag assembly matched to the 
TFR/S which is being repaired. 

CAUTION: Proper operation of the sensors and
supplemental restraint system (SRS) requires that
any repairs to the vehicle structure return it to the
original production configuration.  Deployment 
requires, at a minimum, replacement of the SRS
control unit, air bag assembly and dimensional
inspection of the steering column.  Any visible
damage to the SRS control unit mounting bracket
(s) requires replacement, and the steering column
must be dimensionally inspected, whether
deployment occurred or not. 

Accident With Deployment – Component 
Replacement And Inspections 

Certain SRS components must be replaced or
inspected for damage after a frontal crash involving air
bag deployment.  Those components are: 

•  Air bag assembly 

•  SRS control unit 
 

CAUTION: Refer to “SRS control unit Replacement
Guidelines” below for important information on
SRS control unit replacement in both deployment
and non-deployment crashes. 

•  SRS coil assembly — Inspect wiring and connector 

for any signs of scorching, melting, or damage due
to excessive heat.  Replace if damaged.  Refer to
section “SRS Coil Assembly” in this manual. 

 

 

Accident With or Without Deployment – 
Component Inspection 

Certain SRS system components and rotation parts 
must be inspected after any crash, whether the air bag
has been deployed or not.  Those components are: 

•  Steering column — Refer to Inspection Required 

“After an Accident” in this manual. 

•  Knee bolsters and mounting points — Inspect for 

any distortion, bending, cracking, or other damage.

•  I/P steering column reinforcement plate — Inspect 

for any distortion, bending, cracking, or other 
damage. 

•  I/P braces — Inspect for any distortion, bending, 

cracking, or other damage. 

•  Seat belts and mounting points — Refer to “Seat 

Belts” in Section “Seat Belt” of this workshop 
manual. 

 
SRS Control Unit Replacement Guidelines

SRS control unit replacement policy requires 
replacement of the SRS control unit after a crash 
involving air bag deployment when the “SRS Warning 
Lamp” turned “ON”, the “SRS Diagnosis” should be
done according to Section “Restraint Control System.”

 
Wiring Damage 

If any SRS wire harness is damaged, it should be 
replaced. Don't repair the SRS harness. It is 
replacement only. 

 
SRS Connector (Plastic Body And 
Terminal Metal Pin) Damage 

If any connector or terminal in the SRS wire harness 
(except pigtails) is damaged, it should be replaced. 

 
SRS Wire Pigtail Damage 

If the wiring pigtail (a wire or wires attached directly to 
the device, not by a connector) is damaged, the entire 
component (with pigtail) must be replaced.  Examples 
of “pigtail” components are the driver air bag 
assembly, the passenger air bag assembly, and the 
SRS coil assembly.