Isuzu KB P190. Service manual - part 1412

SUPPLEMENTAL RESTRAINT SYSTEM  9A-13 

Parts Location (LHD) (2) 

 

 

 

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9A-14  SUPPLEMENTAL RESTRAINT SYSTEM 

Component Description 

SRS Control Unit 

WARNING: DURING SERVICE PROCEDURES, BE
VERY CAREFUL WHEN HANDLING A SRS
CONTROL UNIT. NEVER STRIKE OR JAR THE SRS
CONTORL UNIT. NEVER POWER UP THE SRS
WHEN THE SRS CONTROL UNIT IS NOT RIGIDLY
ATTACHED TO THE VEHICLE. ALL SRS CONTROL
UNIT AND MOUNTING BRACKET FASTENERS
MUST BE CAREFULLY TORQUED AND THE
ARROW MUST BE POINTED TOWARD THE FRONT
OF THE VEHICLE TO ENSURE PROPER
OPERATION OF THE SRS. THE SRS CONTROL
UNIT COULD BE ACTIVATED WHEN POWERED
WHILE NOT RIGIDLY ATTACHED TO THE
VEHICLE WHICH COULD CAUSE DEPLOYMENT
AND RESULT IN PERSONAL INJURY. 

The SRS control unit is designed to perform the
following functions in the SRS: 

  1. Energy Reserve — The SRS control unit maintains

30–Volt Loop Reserve (30VLR) energy supply to
provide deployment energy when ignition voltage is
lost in a frontal crash. 

  2. Frontal Crash Detection — The SRS control unit

monitors vehicle velocity changes to detect frontal
crashes which are severe enough to warrant
deployment. 

  3. Air Bag Deployment — When a frontal crash of 

sufficient force is detected, the SRS control unit
will cause enough current to flow through the air
bag assembly to deploy the air bag. 

 4. Malfunction Detection — The SRS control unit 

performs diagnostic monitoring of SRS electrical
components and sets a diagnostic trouble code
when a malfunction is detected. 

  5. Frontal Crash Recording — The SRS control unit

records information regarding SRS status during
frontal crash. 

 6. Malfunction Diagnosis — The SRS control unit

displays SRS diagnostic trouble codes and system
status information through the use of a scan tool. 

  7. Driver Notification — The SRS control unit warns

the vehicle driver of SRS malfunctions by
controlling the “SRS” warning lamp. 

 

 

 

The SRS control unit is connected to the SRS wiring 
harness by a 52–pin connector.  This harness 
connector uses a shorting clip across certain terminals 
in the contact area.  This shorting clip connects the 
“SRS” warning lamp to ground when the SRS control 
unit harness connector is disconnected or CPA 
(Connector Position Assurance) is not inserted even if 
completely connected.  This will cause the “SRS”
warning lamp to come “ON” steady whenever the 
ignition switch is at the ON or START positions with 
the SRS control unit disconnected. 

 

 

 

 

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Legend 

  (1) SRS Control Unit 

  (2) SRS Harness 

 
 

“SRS” Warning Lamp 

Ignition voltage is applied to the “SRS” warning lamp 
when the ignition switch is at the ON or START 
positions.  The SRS control unit controls the lamp by 
providing ground with a lamp driver.  The “SRS” 
warning lamp is used in the SRS to do the following: 

 1. Verify lamp and SRS control unit operation by 

flashing SEVEN (7) times when the ignition switch 
is first turned “ON”. 

  2. Warn the vehicle driver of SRS electrical system 

malfunctions which could potentially affect the 
operation of the SRS.  These malfunctions could 
result in nondeployment in case of a frontal crash 
or deployment for conditions less severe than 
intended. 

The “SRS “ warning lamp is the key to driver 
notification of SRS malfunctions.  For proper lamp 
operation, refer to the “SRS Diagnostic System Check” 
in this section. 

SUPPLEMENTAL RESTRAINT SYSTEM  9A-15 

 

 

 

 

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SRS Coil Assembly 

The SRS coil assembly consists of two current
carrying coils. This is attached to the steering column
and allows rotation of the steering wheel while
maintaining continuous contact of the driver
deployment loop to the driver air bag assembly. 

There is a shorting clip on the yellow connector near
the base of steering column which connects the SRS
coil to the SRS wiring harness. 

The shorting clip shorts to the SRS coil and driver air
bag assembly when the yellow connector is
disconnected.  The circuit to the driver air bag
assembly is shorted in this way to help prevent
unwanted deployment of the air bag when servicing
the steering column or other SRS components. 

 

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Air Bag Assemblies 

The air bag assembly consists of an inflatable air bag 
assembly and an inflator. When the vehicle is in a 
frontal crash of sufficient force the SRS control unit 
causes current flow through the deployment loops. 
Current passing through the inflator ignites the 
material in the air bag assembly. The gas produced 
from this reaction rapidly inflates the air bag assembly.

There is a shorting clip on the driver air bag assembly 
connector which connects the SRS coil assembly. The 
shorting clip shorts across the driver air bag assembly 
circuits when the driver air bag assembly connector is 
disconnected. 

The circuit to the driver air bag assembly is shorted in 
this way to help prevent unwanted deployment of the 
air bag when servicing the driver air bag assembly, the 
steering column or other SRS components. 

 

 

 

 

 

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There is a shorting clip on the passenger air bag 
assembly connector which connects to the SRS 
harness. The shorting clip shorts across the 
passenger air bag assembly circuit when the 
passenger air bag assembly connector is 
disconnected. The circuit to the passenger air bag 
assembly is shorted in this way to help prevent 
unwanted deployment of the air bag when servicing 
the passenger air bag assembly, the instrument panel 
or other SRS components. 

 

9A-16  SUPPLEMENTAL RESTRAINT SYSTEM 

 

 
 
 

 

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Seat Belt with Pretensioner (If so 
equipped) 

The seat belt comprises a seat belt and a cylinder (a
cylinder filled with powder and an ignition device). In
cases of frontal collision which cause a shock
exceeding a specified level, the controller lets current
flow to the inflation circuit. The current ignites the
cylinder of the seat belt, producing gas. The gas helps
tighten the seat belt to restrain firmly the driver’s upper 
half in his seat. 

 

   

 

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Steering Column 

The steering column absorbs energy and is designed 
to compress in a frontal crash to decrease the chance 
of injury to the driver. 

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Knee Bolster 

The knee bolsters are used to absorb energy to 
protect knees and control the forward movement of 
the vehicle's front seat occupants during a frontal 
crash, by limiting leg movement. 

 
Definitions 

Air Bag 
An inflatable cloth cushion designed to deploy in 
certain frontal crashes.  It supplements the protection 
offered by the seat belts by distributing the impact load 
more evenly over the vehicle occupant's head and 
torso. 

Asynchronous 
Performed in a non-periodic fashion, (i.e., no defined 
time or interval). 

B+ 
Battery voltage, (B+) The voltage available at the 
battery at the time of the indicated measurement. 
With the key “ON” and the engine not running, the 
system voltage will likely be between 12 and 12.5 
volts.  At idle, the voltage may be 14 to 16 volts.  The 
voltage could be as low as 10 volts during engine 
cranking.  

Bulb Check 
The SRS control unit will cause the “SRS” warning 
lamp to flash seven times and then go “OFF” 
whenever the ignition switch transitions to the ON 
position from any other ignition switch position and no 
malfunctions are detected.