Isuzu N-Series. Manual - part 1201

SRS CONTROL SYSTEM 9C-51

DTC: 55  Vehicle Type Error

Outline

Description of Circuit
DTC 55 is set when unmatched SRS control unit or SRS
harness installation is suspected.
Turn the starter switch to “ON”. SRS control unit reads
the condition of vehicle type identification terminals 3, 4,
13, 14 for judgment.

Condition when DTC is Set
It is correct when the terminal 4 only is connected to
ground. If the harness is proper, the DTC is set when un-
matched SRS control unit is installed. Also, if the SRS
control unit is proper, the DTC is set when unmatched
harness is installed.

Action to be Taken
SRS control unit turns the “SRS” warning lamp blinking
and set the DTC 55.

However, when both of SRS control unit and SRS har-
ness are faulty, the DTC may not be set.

Condition when DTC is Cleared
When turning the starter switch to OFF with correct
matching of SRS control unit and SRS harness.

Point of Diagnosis
It is correct when the terminal 4 only is connected to
ground. At first, make sure the SRS harness A3, A4,
A13, A14 have no terminal.

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

9C-52 SRS CONTROL SYSTEM

Step

Action

Value

YES

NO

1

Has the “SRS system check” been per-
formed? 

—

Go to Step2

Go to “SRS sys-

tem check”.

2

1. Turn the starter switch to OFF.
2. Remove the harness connector from

SRS control unit.

3. Make sure the “3”, “4”, “13”, “14” of har-

ness connector are in proper condition.

Are the “3”, “4”, “13”, and “14” proper?

—

Replace the SRS 

control unit. Per-

form “SRS system 

check”.

Replace the SRS 
harness. Perform 

“SRS system 

check”.

SRS CONTROL SYSTEM 9C-53

DTC: 61  Warning lamp circuit trouble

Outline

Description of Circuit
Turn the ignition switch to “ON”. Battery voltage is ap-
plied to the “SRS” warning lamp and the “Ignition 1” in-
put terminals “18” and “20”.
SRS control unit responds by blinking “SRS” warning
lamp seven times. SRS control unit monitors lamp driver
output by comparing output condition of the “SRS warn-
ing lamp” terminal “6” with the condition ordered to the
microprocessor.
When the “Ignition 1” is within the specified range, and
the output condition does not match with the condition
ordered by the lamp driver, the DTC 61 is set.

Condition when DTC is Set

1. When no voltage is applied to the SRS control unit

terminal “6” due to open circuit in the meter, burnt
out bulb, or broken harness.

2. When the SRS warning lamp does not go off al-

though the SRS control unit ordered to do so. This
test is performed within 6 seconds after starter
switch is “ON”.

Action to be Taken
SRS control unit sets the DTC 61, and the “SRS” warn-
ing lamp comes ON if its power source and ground line
are normal.

Condition when DTC is Cleared
When turning the starter switch to OFF.

Description of Chart Test
2. Make sure the harness is not broken.
3. Detect if the warning lamp is faulty, and if the SRS
control unit is faulty.

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

9C-54 SRS CONTROL SYSTEM

Point of diagnosis
Warning lamp comes on regardless of SRS control unit
directly, and turns off when the SRS control unit sends
current. Therefore, the warning lamp comes on even
when the SRS control unit fuse is blown out if there is no
other trouble.

Step

Action

Value

YES

NO

1

Has the “SRS system check” been per-
formed?

—

Go to Step2

Go to “SRS sys-

tem check”.

2

Turn the starter switch to OFF.

Do warning lamps other than “SRS” operate
properly?

—

Go to Step4

Go to Step3

3

Replace the meter assembly.

Is this step completed?

—

Go to Step5

Go to Step3

4

1. Wiring is open between SRS control unit

and SRS warning lamp, or it is shorted
with body, or “SRS” warning lamp is
blown out.

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

lem.

Has the cause been detected and repaired?

—

Go to Step5

Go to Step4

5

1. Reconnect all the parts, and check that

those are installed properly.

2. Clear the DTC.

Is this step completed?

—

Check the repair.

Go to Step5