Isuzu N-Series. Service manual — part 1192
SRS CONTROL SYSTEM 9C-15
Standard
In case of collision: In any case of collision regardless of
SRS airbag deployment
In case of trouble: In case trouble code is detected with
Tech 2 diagnosis when “SRS” warning lamp does not
come on or remains on.
List of Function Checks
SRS System Check
Outline
The purpose of the diagnostic procedure in this topic is
to find SRS function faults and repair them. For best re-
sults, it is important to use diagnostic chart and follow
the order indicated as follows.
A. Perform “SRS system check”.
Always begin with “SRS system check” for SRS diagno-
sis.
“SRS system check” includes whether “SRS” warning
lamp operates properly, and whether SRS control unit
can communicate via “serial data” line, and if SRS diag-
nostic trouble code exists.
B. Refer to appropriate diagnostic chart according
to the instruction of “SRS system check”.
Go on to the appropriate chart to diagnose SRS function
fault with “SRS system check”. Failure to perform this
procedure leads to longer diagnosis period, wrong diag-
nosis or replacement of wrong part.
C. Repeat “SRS system check” after performing re-
pair and diagnostic procedure.
“SRS system check” after every repair or diagnostic pro-
cedure can confirm correct repair work and if other func-
tion fault exists.
Rele-
vant
parts
Steering column
❍
• Shaft and shaft support bracket are deformed.
• Tilt operation cannot be performed smoothly.
Instrument panel,
crossbeam, cover, etc.
Glove box
Seat
Seat belt
Windshield glass
❍
• Dent, bent, chapped, cracked, or deformed.
• Replace the seat belt which were used in collu-
sion.
Counterpart
❍
• If it is dent, bent, chapped, cracked, or deformed,
repair or replace with new one.
• If installation is loose, tighten the to the specified
torque.
Description
Standard
Standard for parts replacement
In case of
collision
In case of
trouble/
periodical
inspection
Item to be checked
Contents of inspection
SRS system check
Inspection to identify defective point of SRS control system (inspection pro-
cedure)
SRS control unit function check
(Chart A)
Inspection to identify function fault of SRS control unit (inspection proce-
dure)
“SRS” warning lamp turns on contin-
uously (Chart B)
Check when “SRS” warning lamp turns on continuously when starter switch
is turned ON.
“SRS” warning lamp does not come
on (Chart C)
Check when “SRS” warning lamp does not come on when starter switch is
turned ON.
9C-16 SRS CONTROL SYSTEM
Description of Circuit
Once the starter switch is turned to “ON”, ignition volt-
age is applied from “SRS fuse” to “Ignition A” input ter-
minal “20” and “Ignition B” input terminal “18” of SRS
control unit. SRS control unit executes tests related to
SRS, and “SRS” warning lamp responds by blinking
seven times.
Cautions at Each Step of “SRS System Check”
(Numbers below indicate step numbers in the system
check.)
1. Turn the starter switch to “ON”, and check that the
“SRS” warning lamp blinks seven times.
2. Check that the “SRS” warning lamp goes off after it
blinks seven times.
3. This test is to check whether “serial data” line op-
erates properly. Also, it detects whether history
trouble codes are stored, and confirms the code if
stored.
4. This test is to check whether “serial data” line oper-
ates properly. Also, it confirms the stored history
trouble codes, and confirms whether those are cur-
rent code or history code.
Point of Diagnosis
Order is very important to diagnose diagnostic trouble
code. Be sure to diagnose in the specified order. Failure
to do so leads to longer diagnosis period, wrong diagno-
sis or replacement of wrong part.
Diagnostic Aid
The intermittent “SRS” warning lamp illumination may
be caused by poor contact, worn wire insulation or dis-
connection in insulation. Check for following conditions:
• Check for improper connection of the SRS control
unit harness and the connector, lock breakage, de-
formation or damage of the terminal, poor contact
between the terminal and the wire, and damaged
harness.
Step
Action
Value
YES
NO
1
Turn the starter switch to “ON”, and check the
“SRS” warning lamp operation.
Does the “SRS” warning lamp blink seven
times?
—
Go to Chart C
“SRS” warning
lamp does not
come on.
2
Check the “SRS” warning lamp operation after
it blinks seven times.
Does the “SRS” warning lamp go off?
—
3
1. Turn the starter switch to OFF.
2. Connect the Tech 2 with diagnosis con-
nector, and follow the instruction on Tech
2 manual.
3. Turn the starter switch to ON.
4. Request SRS diagnostic trouble code
display, and record all the history trouble
code in the repair order with taking notes
that it is recorded in this manner.
Is the diagnostic trouble code displayed?
—
Turn the starter
switch to OFF.
Refer to “Point of
diagnosis” of
other specific
DTC for all the
history code. His-
tory DTC indi-
cates that the
function fault has
been corrected or
it is intermittent.
SRS is in function,
and there is no
function fault. Fur-
ther diagnosis is
not necessary.
SRS CONTROL SYSTEM 9C-17
4
1. Turn the starter switch to OFF.
2. Connect the Tech 2 to the diagnosis con-
nector.
3. Turn the starter switch to ON.
4. Confirm the diagnostic trouble code
(DTC) using Tech 2, and record all the
DTC in the repair order with taking notes
that it is current code or history code if it
appears.
Is the diagnostic trouble code (DTC) dis-
played?
—
If DTC 51 is dis-
played, go to DTC
51 chart. If DTC
53 is displayed,
go to DTC 53
chart. If DTC 25 is
displayed, go to
DTC 25 chart. If
DTC 71 is dis-
played, go to DTC
71 chart.
Diagnose rest of
the current DTC in
the order from
lower level. Refer
to “Point of diag-
nosis” of the spe-
cific DTC, if only
history codes
exist.
Go to Chart B
“SRS” warning
lamp turns on
continuously.
Step
Action
Value
YES
NO
9C-18 SRS CONTROL SYSTEM
Chart A SRS Control Unit Function Check
Outline
Description of Circuit
If either of the “Ignition A” voltage applied to terminal
“20” or “Ignition B” voltage applied to terminal “18” ex-
ceeds 10V, the airbag SRS control unit recognizes it and
“SRS” warning lamp blinks seven times to confirm oper-
ation. At this point, SRS control unit performs “Initial di-
agnosis” and “Constant diagnosis” subsequently. Once
function fault is detected, SRS control unit set the cur-
rent diagnostic trouble code and turn “SRS” warning
lamp to ON.
When SRS control unit does not detect any more func-
tion fault except DTC 25, 51, 53, 71, it clears the current
diagnostic trouble code moving them to the EEPROM.
Trouble codes cannot be cleared but with “Clear code”
command of Tech 2, except following DTCs. In addition,
“Clear code” command cannot clear DTCs 25, 51, 53,
and 71.
Description of Chart Test
Numbers below indicate step numbers in the diagnostic
chart.
1. This test is to confirm current function fault. Refer to
“Point of diagnosis” of appropriate DTC, if there is no
current function fault (history DTC is set). Do not replace
the SRS control unit because of history diagnostic trou-
ble code.
2. Confirm diagnostic trouble code using Tech 2.
3. This test is to check function fault occurred in the SRS
control unit during diagnosis. Function fault of SRS con-
trol unit hardly cause new function fault during diagno-
sis.
B
ACC
ON
ST
STARTER SWITCH
METER
AIRBAG
SRS CONTROL UNIT
DATA LINK CONNECTOR
16 15 14 13 12 11 10 9
8 7 6 5 4 3 2 1
0.5
B
0.5
GY
0.5
SB
0.5
GY
0.5
SB
16
4
19
15
18
7
8
20
6
5
0.85B
0.85B
0.5
B/R
0.5
B/R
0.5
W/R
0.5
B/R
0.5
B/R
0.5
W/R
0.5
B
1.25
B
2L
3
B/Y
2
14
3W/L
8B
3W/L
40A
KEY SW
10A
SRS
AIRBAG
SRS COIL
ASSEMBLY
1
2
2
1
0.5
Y
0.5
Y/B
3
10A
METER
0.5
B/Y
18
OFF
N9A0086E
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