Isuzu N-Series. Manual - part 1193

SRS CONTROL SYSTEM 9C-19

4. Replace the SRS control unit only when all circuits ex-
cept SRS control unit are confirmed to be functioning
properly. Failure to do so may cause inerasable code
stored in the SRS control unit and it may requires re-
placement again.

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.

WARNING:

DURING SERVICE WORK, BE CAREFUL NOT TO
TAP OR SHAKE THE SRS CONTROL UNIT. ALSO,
FAILURE TO INSTALL THE SRS CONTROL UNIT TO
VEHICLE PROPERLY MAY LEAD TO MALFUNC-
TION OF THE UNIT WHEN THE STARTER SWITCH IS
TURNED TO ON. THIS MAY RESULT IN INJURY DUE
TO SUDDEN DEPLOYMENT OF SRS AIRBAG.

Step

Action

Value

YES

NO

1

1. This chart is based on the assumption

that “SRS system check” diagnosis has
been performed. Perform the following
procedure when the chart shows and
proves that all circuits except SRS control
unit are confirmed to be functioning prop-
erly, and DTC remains stored as current
code.

2. Perform the diagnostic procedure to

check if the SRS control unit has to be re-
placed.

3. Turn the starter switch to OFF.
4. Connect all the system components, and

make sure those are installed properly.

5. Make sure that the starter switch is “OFF”

at least for 15 seconds. 

6. Turn the starter switch to “ON”, and check

the “SRS” warning lamp operation.

Does the “SRS” warning lamp go off after it
blinks seven times?

—

Go to Step3

Go to Step2

2

Request diagnostic trouble code display using
Tech 2.

Is there any other DTC than that appeared at
the “SRS system check” in the beginning?

—

Turn the starter 

switch to OFF. Go 

to appropriate 

chart according to 

the function fault 

indicated.

Go to Step3

3

1. Clear the SRS DTC.
2. Turn the starter switch to OFF at least for

15 seconds. Turn the starter switch to
“ON”, and check the “SRS” warning lamp
blinking operation.

Does the “SRS” warning lamp go off after it
blinks seven times?

—

System is in func-

tion, and there is 
no function fault. 

Further diagnosis 

is not necessary.

Turn the starter 

switch to OFF. Go 

to Step4

9C-20 SRS CONTROL SYSTEM

Chart B  “SRS” Warning Lamp Turns on Continuously

Outline

Description of Circuit
Turn the starter switch to “ON”. Battery voltage is ap-
plied to “SRS” warning lamp and the “SRS” warning
lamp comes ON.
“SRS fuse” can apply system voltage to the “Ignition” in-
put terminal “20” and “18”. After “SRS” warning lamp

blinks seven times, SRS control unit calls warning lamp
drive circuit in the SRS control unit to turn the “SRS”
warning lamp off, if there is no current DTC.
If the “Ignition” voltage is less than 10V, “SRS” warning
lamp turns on continuously, and no DTC is set.

4

1. Replace the SRS control unit.
2. Connect all the SRS components, and

check that those are installed properly.

3. Connect the Tech 2, and check if “Event

data clear prohibition” flag is displayed.

4. If not, put the flag up.

Is this step completed?

—

Check the repair.

Go to Step4

Step

Action

Value

YES

NO

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

SRS CONTROL SYSTEM 9C-21

Description of Chart test
Numbers below indicate step numbers in the diagnostic
chart.
1. This test is to check if power is provided to the SRS
control unit feeder circuit.

2. This test is to check if the “Ignition” and ground circuit
is normal against the SRS control unit.
3. This test is to check if the location of function fault is
in the SRS control unit.
4. This test is to check ground short circuit from the SRS
control unit feeder circuit.

Step

Action

Value

YES

NO

1

1. Turn the starter switch to OFF.
2. Remove the “SRS fuse” of SRS airbag to

inspect.

Is the fuse normal?

—

Go to Step2

Go to Step4

2

1. Turn the starter switch to OFF.
2. Disconnect the SRS control unit harness

connector.

3. Remove the 2-pole connector (yellow) lo-

cated in the lower portion of steering col-
umn.

4. Turn the starter switch to ON.
5. Measure the voltage between the SRS

control unit harness connector terminals
“20” and “16”.

Is the voltage 18V?

—

Go to Step3

Go to Step5

3

1. Turn the starter switch to OFF.
2. Connect all the parts.
3. Connect the Tech 2, and turn the starter

switch to ON.

4. Check if “Event data clear prohibition”

flag is displayed.

Is the flag displayed?

—

Put the “Event 

data clear prohibi-

tion” flag up.Go to 

Step7

Go to Chart A 

SRS control unit 

function check.

4

1. Replace the “SRS fuse”.
2. Turn the starter switch to ON, and wait for

10 seconds. Then, turn the starter switch
to OFF.

3. Remove the “SRS fuse” to inspect.

Is the fuse normal?

—

Install the fuse 

and Go to Step7.

Go to Step6

5

1. The power supply circuit of SRS control

unit or ground circuit is open.

2. Find the cause.
3. Replace the SRS harness, if it has prob-

lem.

Is this step completed?

—

Go to Step7

Go to Step5

6

1. The power supply circuit of SRS control

unit is shorted.

2. Find the cause.
3. Replace the SRS harness, if it has prob-

lem.

Is this step completed?

—

Go to Step4

Go to Step6

7

Reconnect all the parts, and check that those
are installed properly.

Is this step completed?

—

Check the repair.

Go to Step7

9C-22 SRS CONTROL SYSTEM

Chart C  “SRS” warning lamp does not come on

Outline

Description of Circuit
Turn the starter switch to “ON”. Battery voltage is ap-
plied to “SRS” warning lamp and the “SRS” warning
lamp comes ON.
“SRS fuse” can apply system voltage to the “Ignition” in-
put terminal “20” and “18”.
After “SRS” warning lamp blinks seven times, SRS con-
trol unit calls warning lamp drive circuit in the SRS con-
trol unit to turn the “SRS” warning lamp off, if there is no
current DTC.
If the “Ignition” voltage is less than 10V, “SRS” warning
lamp turns on continuously, and no DTC is set.

Description of Chart test
Numbers below indicate step numbers in the diagnostic
chart.
1. This test is to check if power is provided to the SRS
warning lamp feeder circuit.
2. This test is to check if SRS control unit operates im-
properly to prevent the “SRS” warning lamp from coming
on.
3. This test is to check if the circuit between warning
lamp and SRS control unit is shorted to ground.
4. This test is to check if “SRS” warning lamp circuit is
normal.
5. This test is to check ground short circuit from the SRS
warning lamp feeder circuit.

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