display ISUZU TF SERIES 2004 Workshop Manual

9A-8 SUPPLEMENTAL RESTRAINT SYSTEM

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
“AIR BAG” 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 “AIR BAG”
warning lamp to come “ON” steady whenever the
ignition switch is at the ON or START positions with
the SRS control unit disconnected.


060R300008
Legent
(1) SRS Control Unit
(2) SRS Harness
(3) Connector Position Assurance

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
24–
Volt Loop Reserve (24VLR) energy supply to
provide deployment energy when ignition voltage is
lost in a frontal crash.
2. Frontal Crash Detection — The SRS control uni
t
monitors vehicle velocity changes to detect frontal
crashes which are severe enough to warran
t
deployment.
3. Air Bag Deployment — When a frontal crash o
f
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 uni
t
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 uni
t
records information regarding SRS status during
frontal crash.
6. Malfunction Diagnosis —The SRS control uni
t
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 b
y
controlling the “Air Bag” warning lamp.




“Air Bag” Warning Lamp
Ignition voltage is applied to the “AIR BAG” 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 “AIR BAG”
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 “AIR BAG “ 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.

9A-26 SUPPLEMENTAL RESTRAINT SYSTEM

Tech 2 Scan Tool
From 98 MY, Isuzu dealer service departments are
recommended to use Tech 2. Please refer to Tech 2
scan tool user guide.
901RW200
Legent
(1) PCMCIA Card
(2) RS 232 Loop Back Connector
(3) SAE 16/19 Adaptor
(4) DLC Cable
(5) Tech-2

Getting Started
 Before operating the Isuzu PCMCIA card with the
Tech 2, the following steps must be performed:
1. Insert the Isuzu System PCMCIA card (1) into the
Tech 2 (5).
2. Connect the SAE 16/19 adapter (3) to the DLC
cable (4).
3. Connect the DLC cable to the Tech 2 (5)
4. Make sure of the vehicle ignition is off.
5. Connect the Tech 2 SAE 16/19 adapter to the
vehicle DLC connector.


060R300015
6. Turn on the vehicle ignition switch.
7. Verify the Tech 2 power up display.
060RW009
NOTE:The RS232 Loop back connector is only used
to diagnosis Tech 2. Refer to user guide of the Tech 2.

9A1-4 RESTRAINT CONTROL SYSTEM

cautions in the service manual and on warning labels
attached to SRS components.

Basic Electrical Circuits
You should understand the basic theory of electricity
including series and parallel circuits, and understand
the voltage drops across series resistors. You should
know the meaning of voltage (volts), current (amps),
and resistance (ohms). You should understand what
happens in a circuit with an open or a shorted wire. You
should be able to read and understand a wiring
diagram.

“Flash Code” Diagnostics
Flash code diagnostics can be used to read active
codes and to determine if history codes are present but
cannot be used to clear codes or read history codes.
Flash code diagnostics is enabled by grounding by
terminal 4 shorting to terminal 13 of the DLC connector
with the ignition switch “ON”. Grounding terminal 4 of
the DLC connector pulls the “Diagnostics Request”
input (Terminal 1) of the SRS control unit low and
signals the SRS control unit to enter the flash code
diagnostic display mode.


060R300052

RESTRAINT CONTROL 9A1-5

The SRS control unit displays the trouble codes by
flashing the warning lamp. Each code that is displayed
will consist of a number of flashes which represents the
tens digit, a 1.2 second pause, following by a number of
flashes which represents the ones digit of the code.
Each code is displayed one time before moving on to
the next code. After all of the codes have been
displayed, the entire code sequence will continually by
repeated until ground is removed from terminal 4 of the
DLC connector.


Two special codes exist when reading in the flash code
mode (Flash Code 12 and Flash Code 13). “Flash
Code 12” will always be the first code displayed when
the flash code mode is enable Code 12 is not an
indication of a SRS problem but an indication that the
flash code mode has been enabled. If there are no
active or history codes present, the SRS control unit will
display code 12 until ground is removed from the DLC
connector at terminal 4. “flash Code 13” will be
displayed if history codes are present. To read the
history codes a scan tool must be used.


060R300051
DATA LIST (Tech 2)









DISPLAY on Tech 2 UNIT VALUE
Driver Airbag Loop
Enabled/Disabled
Passenger Airbag Loop
Enabled/Disabled
System Voltage V 12.0
Driver Seat Belt Status
Not Backled/Backled

9A1-6 RESTRAINT CONTROL SYSTEM

Diagnostic Trouble Codes
Choose and trace an appropriate flowchart by the numbers listed below to find fault and repair.
DTC
(Flash
Code) Description
—
(12) Diagnostic Display Mode (Flash Code only)
—
(13) Diagnostic Display Mode (Flash Code only)
B0016
(16) Passenger Airbag Squib Circuit Low Resistance
B0017
(17) Passenger Airbag Squib Circuit High Resistance
B0018
(18) Passenger Airbag Squib Circuit Voltage Range / Performance
B0022
(22) Driver Airbag Squib Circuit Low Resistance
B0024
(24) Driver Airbag Squib Circuit Voltage Range / Performance Resistance
B0026
(26) Driver Airbag Squib Circuit High Resistance
B0033
(33) ECU Connector Poor Connection
B0051
(51) Squib Circuit Activated (Clash)
B0053
(53) Deployment Command Despite Present Trouble Code
B0057
(57) Passenger Pretensioner Squib Circuit Low Resistance
B0058
(58) Passenger Pretensioner Squib Circuit High Resistance
B0059
(59) Passenger Pretensioner Squib Circuit Voltage Range / Performance
B0064
(64) Driver Pretensioner Squib Circuit Low Resistance
B0065
(65) Driver Pretensioner Squib Circuit High Resistance
B0066
(66) Driver Pretensioner Squib Circuit Voltage Range / Performance Resistance
B0670
(63) Airbag Telltale Circuit Malfunction
B1000
(72) SDM Internal Fault (SDM= SRS control unit)

9A1-8 RESTRAINT CONTROL SYSTEM

Circuit Description
When the ignition switch is first turned “ON”, “Ignition 1”
voltage is applied from the “SRS” fuse to the SRS
control unit at the “Ignition 1” input terminals “35”. The
SRS control unit responds by flashing the “AIR BAG”
warning lamp seven times, while performing tests on
the SRS.

Notes On System Check Chart
1.
The “AIR BAG” warning lamp should flash seven
times after ignition is first turned “ON”.
2.
After the “AIR BAG” warning lamp flashes seven
times, it should turn “OFF”
3.
This test checks for the proper operation of the
“Serial Data” line. This test will also determine
whether history diagnostic trouble codes are stored
and, if so, identify them.
4.
Improper operation of the “AIR BAG” warning lamp
is indicated. This test differentiates a warning lamp
stays “ON” condition from a warning lamp does not
come “ON” condition.
5.
This test checks for proper operation of the “Serial
Data” line. This test will also identify the stored
diagnostic trouble codes and whether they are
current or history.
Diagnostic Aids
The order in which diagnostic trouble codes are
diagnosed is very important. Failure to diagnose the
diagnostic trouble codes in the order specified may
result in extended diagnostic time, incorrect diagnosis
and incorrect parts replacement.


SRS Diagnostic System Check
Step Action Yes No
1 Note the “Air Bag” warning lamp as ignition switch is turned “ON.”
Does the “AIR BAG” warning lamp flash seven 7 times? Go to Step 2 Go to Step 3
2 Note the “AIR BAG” warning lamp after it flashed 7 times.
Does the “AIR BAG” warning lamp go “OFF”? Go to Step 4 Go to Step 5
3 Note the “AIR BAG” warning lamp as ignition switch is turned
“ON”.
Does the “AIR BAG” warning lamp come “ON” steady? Go to Chart B. Go to Chart C.
4
1.
Note the “AIR BAG” warning lamp as that ignition switch is
turned “ON.”

Ignition switch “OFF.”

2.
Connect a scan tool to data link connector.

3.
Follow direction given in the scan tool instruction manual.

Ignition switch “ON.”

4.
Request the SRS diagnostic trouble code display, recode all
history diagnostic trouble code(s). specify as such, on repair
order
Is (are) diagnostic trouble code(s) displayed? Ignition switch
“OFF.”
When DTC B1000 is
set, go to DTC
B1000 Chart.
For all other history
codes refer to
“Diagnostic Aids”
For that specific
DTC.
A history DTC
indicates the
malfunction has
been repaired or is
intermittent. SRS is functional
and free of
malfuncitons, no
further diagnosis is
required.
If scan tool indicated
“NO DATA
RECEIVED,” refer to
chassis electrical
section 8.

RESTRAINT CONTROL 9A1-9

Step Action Yes No
5
1. Ignition switch “OFF.”
2. Connect a scan tool to data link connector.

3. Follow directions as given in the scan tool instruction
manual.

4. Ignition switch “ON.”
5. Request the SRS diagnostic trouble code display, Recode
all diagnostic trouble code(s), specifying as current or history
on repair order.
Is (are) diagnostic trouble code (s) displayed? Ignition switch
“OFF”.
When DTC B0053 is
set, go to DTC
B0053 chart.
When DTC B0051 is
set, go to DTC
B0051 chart.
When DTC B0018
is set, go to DTC
B0018 chart.
When DTC B0024
is set, go to DTC
B0024 chart.
Diagnose remaining
current DTCs from
lowest to highest.
When only history
DTCs exist, refer to
“Diagnostics Aids”
for that specific
DTC.
A history DTC
indicates the
malfunction has
been repaired or is
intermittent. If scan tool indicates
“No Data Received,”
refer to chassis
electrical section 8.

RESTRAINT CONTROL 9A1-11

3.
When all circuitry outside the SRS control unit has
been found to operate properly, as indicated by the
appropriate diagnostic chart, then and only then
should the SRS control unit be replaced.


Chart A SRS control unit Integrity Check
WARNING: DURING SERVICE PROCEDURES. BE VERY CAREFUL WHEN HANDLING A SRS CONTROL
UNIT. NEVER STRIKE OR JAR THE SRS CONTROL 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 POINTING 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

Step Action Yes No
1

1. This chart assumes that the “SRS Diagnostic System
Check” and either a symptom chart or a diagnostic trouble
code chart diagnosis have been performed. When all
circuitry outside the SRS control unit has been found to
operate properly, as indicated by the appropriate diagnostic
chart, and the symptom or DTC remains current, the
following

2. Diagnostic procedures must be performed to verify the need
for SRS control unit replacement.

3. Ignition switch “OFF”.
4. Reconnect all SRS components, ensure all components are
properly mounted.

5. Ensure the ignition switch has been “OFF” for at least 15
seconds.

6. Note “AIR BAG” warning lamp as ignition switch is turned
“ON.”
Does warning lamp flash 7 times then go “OFF”? The symptom or
DTC is no longer
occurring.
Clear SRS
diagnostic trouble
codes.
Repeat “SRS
Diagnostic System
Check” Go to Step 2
2 Using a scan tool request diagnostic trouble code display.
Is the same symptom or DTC occurring as was when the “SRS
Diagnostic System Check” was first performed? Go to Step 3 Ignition switch
“OFF”.
Go to the
appropriate chart for
the indicated
malfunction.
3
1. Clear “SRS Diagnostic Trouble Codes”.

2. Ignition switch “OFF” for at least two minutes.

3. Note “AIR BAG” warning lamp as ignition switch is turned
“ON.”
Does warning lamp flash 7 times then go “OFF”? SRS is functional
and free of
malfunctions.
No further diagnosis
is required.
Go to Step 4 Ignition switch
“OFF”.
Replace SRS control
unit.
Go to Step 4
4 Reconnect all SRS components, ensure all components are
properly mounted.
Was this step finished? Repeat the “SRS
Diagnostic System
Check” Go to Step 4

RESTRAINT CONTROL 9A1-13

Chart B “AIR BAG” warning lamp comes “ON” Steady

Step Action Yes No
1

1. When measurements are requested in this chart use 5-8840-
0285-0 DVM with correct terminal adapter from 5-8840-
0385-0.

2. Ignition switch “OFF.”

3. Connect scan tool to data link connector, follow directions as
given in the scan tool instruction MANUAL.

4. Ignition switch “ON.”

5. Request SRS diagnostic trouble code display.
Dose scan tool indicate “No Data Received”? Go to Step 2 Go to Step 3
2

1. Ignition switch “OFF”.

2. Inspect SRS control unit harness connector connection to
SRS control unit.
Is it securely connected to the SRS control unit? Ignition switch
“OFF.”
Replace SRS
control unit.
Go to Step 5 Connect SRS
control unit
securely to de–
activate shorting
clip in SRS control
unit harness
connector.
Go to Step 5
3 Using scan tool, request SRS data list.
Is “ignition” more than 9 volts? Go to Step 4 Ignition switch
“OFF.”
Replace SRS
control unit.
Go to Step 5
4

1. Ignition switch “OFF.”

2. Disconnect SRS coil and passenger air bag assemblies.
yellow connector located at base of steering column and
behind the glove box assembly.
Disconnect SRS control unit.

3. Disconnect the connector of “SRS Warning Lamp” of
instrument cluster.

4. Measure resistance from SRS control unit harness connector
terminal “40” to ground.
Does 5-8840-0285-0 DVM display “OL” (Infinite)? Go to Chart A Replace SRS
harness.
Go to Step 5
5 Reconnect all SRS components, ensure all components are
properly mounted.
Was this step finished? Repeat the “SRS
Diagnostic System
Check” Go to Step 5

9A1-24 RESTRAINT CONTROL SYSTEM

DTC Will Clear When
This malfunction is no longer occurring and the ignition
switch is turned “OFF”.

DTC Chart Test Description
Number(s) below refer to circled number(s) on the
diagnostic chart.
2.
This test determines whether the SRS control unit is
malfunctioning.
3.
This test isolates the malfunction to one side of the
passenger air bag assembly yellow connector behind
glove box compartment.
4.
This test determines whether the malfunction is in
“Passenger Bag High” circuit.
5.
This test determines whether the malfunction is in
“Passenger Bag Low” circuit.
6.
This test determines whether the malfunction is in
“Driver Bag High” circuit.
7.
This test determines whether the malfunction is in
“Driver Bag Low” circuit.
Diagnostic Aids
An intermittent condition is likely to be caused by a short
to ground/+B in the passenger air bag assembly circuit.
Inspect circuits “Passenger Bag High” and “Passenger
Bag Low” carefully for cutting or chafing. If the wiring
pigtail of the passenger air bag assembly is damaged,
the component must be replaced.


DTC B0018 (Flash Code 18) Passenger Airbag Squib Circuit Voltage Range/Performance

Step Action Yes No
1 Was the “SRS Diagnostic System Check” performed? Go to Step 2 Go to the “SRS
Diagnostic System
Check”
2

1. When measurements are requested in this chart use 5-8840-
0285-0 DVM with correct terminal adapter from 5-8840-
0385-0.

2. Ignition switch “OFF.”

3. Ignition switch “ON.”

4. Check the passenger air bag squib circuit for short to voltage,
short to ground and open.
Was a problem found? Go to Step 3


3

1. Ignition switch “OFF.”

2. Disconnect passenger air bag assembly yellow connector
behind the glove box assembly.
3. Leave driver air bag assembly connected.

4. Connect SRS driver / passenger load tool 5-8840-2421-0 and
appropriate adapter to passenger air bag assembly harness
connector.
5. Ignition switch “ON.”
Is DTC B0018 current? Go to Step 4 Ignition switch
“OFF.”
Replace
passenger air bag
assembly .
Go to Step 8
4

1. Ignition switch “OFF”.

2. Disconnect SRS driver / passenger load tool
3. Measure resistance on SRS control unit harness connector
from terminal “48” to terminal “40” (ground).
Does 5-8840-0285-0 display “OL” (Infinite)? Go to Step 5 Replace SRS
Harness.
Go to Step 8
5 Measure resistance on SRS control unit harness connector from
terminal “47” to terminal “40” (ground).
Does 5-8840-0285-0 display “OL” (Infinite)? Go to Step 6
Replace SRS
Harness.
Go to Step 8