Isuzu N-Series. 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 Step2

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?

—

Go to Step3

Go to Step4

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