Isuzu N-Series. Service manual - part 1191

SRS CONTROL SYSTEM 9C-11

H-7

Procedure of Trouble Diagnosis

Diagnostic Trouble Code (Self-diagnosis Code)
At first, perform “SRS system check”. “SRS system
check” is to check whether “SRS” warning lamp oper-
ates properly and confirms SRS diagnostic trouble code
(DTC) using warning lamp blinking or Tech 2.

1. Active diagnostic trouble code: Function fault cur-

rently detected. Active diagnostic trouble codes
are stored in the RAM (Random Access Memory).
(Code of current trouble)

2. History diagnostic trouble code: Function fault de-

tected after history memory had been cleared last
time. History diagnostic trouble codes are stored in
the EEPROM. (Trouble code occurred in the past)

System Diagnostic Method
System diagnostic method is a standardized method to
repair all the electric/electronic (E/E) systems. Diagnos-
tic procedure is always used to solve the problem of E/
E system and is a starting point when service is re-
quired. Procedure of diagnosis is described in the fol-
lowing steps:

1. Confirm a customer’s complaint.

• It is necessary for technicians to understand the

normal operations of the systems to confirm a
customer’s complaint.

2. Perform pre-inspection.

• Perform overall visual check.
• Review service record.
• Detect noise or abnormal odor.
• Collect the diagnostic trouble code information

for effective repair.

3. Check service information.

• This includes video, news letter, etc.

If DTC is Stored
Perform service correctly according to the specified
DTC chart.

If there is No DTC
Select symptom from the diagnostic chart according to
symptom. Complete the service following diagnostic
procedure. You may also perform inspection by refer-
ring function diagnosis.

If there is No Applicable Symptom

1. Confirm the complaint in detail.
2. Create diagnostic plan.
3. Use wiring diagram and principle of operation.

Ask for technical support when repair history is available
for similar case. Connect technician’s knowledge with
the effective usage of available service information.

If there is Intermittent (Intermittent Trouble)
The trouble situation not occurring constantly is called
intermittent (intermittent trouble). Perform the following
steps to solve the intermittent trouble.

1. Check the DTC information and SRS data.
2. Evaluate symptom and situation explained by the

customer.

3. Check the circuits or the electric system compo-

nents using check sheet or other methods.

If the Trouble is not Detected
In this case, the vehicle is judged as it operates properly.
The condition explained by the customer may be the
normal condition. Confirm the customer’s complaint
comparing with the condition of the vehicle to that of an-
other vehicle. That condition may mean an intermittent
trouble. Confirm the complaint in the situation the cus-
tomer explains before returning the vehicle to the cus-
tomer.

1. Confirm the complaint again.

If the complaint can not be fully detected or identi-
fied, the vehicle must be diagnosed again. Confirm
the complaint one more time. The complaint may
be an intermittent trouble as defined in “If there is
intermittent”, but it may also be possible that the
vehicle is normal.

P-4

P-5

No.

Connector Face

000-004

000-002

1 2 3 4

5 6 7 8

9 10 11 12 13

14 15 16 17 18

4 3 2 1

8 7 6 5

13 12 11 10 9

18 17 16 15 14

H - 6

H - 7

H - 8

N8A5489E

9C-12 SRS CONTROL SYSTEM

2. Repair and confirm.

If the problem is confirmed, repair it. Confirm that
the vehicle operates properly and the symptoms
are corrected.
This includes road test or other procedures to con-
firm that the trouble is solved under following con-
ditions:

• Confirm by testing in the situation that the cus-

tomer described.

• If DTC is diagnosed, while monitoring Tech 2

data, reproduce the situation found when the
DTC is set, and confirm the repair.

About Diagnostic Procedure

WARNING:

WHEN SERVICING SRS, DO NOT USE ELECTRICAL
TEST EQUIPMENT EXCEPT ONES DESCRIBED IN
THIS MANUAL TO AVOID DEPLOYMENT OF SRS
AIRBAG. FAILURE TO FOLLOW THIS MANUAL MAY
CAUSE INJURY DUE TO UNNECESSARY DEPLOY-
MENT OF SRS AIRBAG.

The purpose of the diagnostic procedure in this topic is
to find SRS problems and repair them. The procedures
to find SRS problems quickly and repair effectively is de-
scribed as follows. Failure to perform this procedure
leads to longer diagnosis period, wrong diagnosis or re-
placement of wrong part.

1. Perform pre-inspection.
Always begin the diagnosis with the followings.

• Perform overall visual check. (Such as improper

connection of terminal, wire, etc., trace of water
(coffee, juice, etc.) contact with SRS control unit)

• Review service record.
• Detect noise or abnormal odor.

2. Perform “SRS system check”.
“SRS system check” includes whether “SRS” warning
lamp operates properly and SRS diagnostic trouble
code check using “warning lamp blinking” or “Tech 2”.

3. Refer to appropriate diagnostic chart according
to the instruction of “SRS system check”.
Go on to the appropriate chart to diagnose SRS prob-
lems with “SRS system check”. Failure to perform this
procedure leads to longer diagnosis period, wrong diag-
nosis or replacement of wrong part.

4. Repeat the “SRS system check” after performing
repair and diagnostic procedure.
“SRS system check” after every repair or diagnostic pro-
cedure can confirm correct repair work and if other prob-
lem exists.

About Diagnostic Code
SRS control unit records troubles occurred in the past
after the trouble code had been cleared last time.

1. Active code (trouble code occurring currently)
Troubles currently detected during this ignition cycle.
Active codes are stored in the RAM (Random Access
Memory).

2. History code (trouble code occurred in the past)
All troubles detected after history trouble memory had
been cleared last time.
History codes are stored in EEPROM (Electrically Eras-
able Programmable Read Only Memory).

Necessary Basic Knowledge
Certain basic knowledge is required before using this
topic of the manual. Absence of this knowledge
cause difficulty when using diagnostic procedure in this
topic. Be cautious to protect from harmful or unneces-
sary deployment. Be sure to read and understand every
caution on the caution label attached to SRS parts as
well as the service manual.

Basic Electrical Circuit
Understand the basic electrical theory including serial
and pararel circuits, and understand voltage drop in the
series resistance. Understand the meaning of voltage,
current (ampere), resistance (ohm), and what happens
on the circuit by bare wire or short circuit. You must be
able to read and understand wiring diagram.

How to Read Trouble Code
By connecting diagnosis connector, trouble records are
displayed by blinking of warning lamp.
Also Tech 2 can read (and clear excluding some code)
all codes (current and history codes).

SRS CONTROL SYSTEM 9C-13

Flash Code Diagnosis
Using SRS warning lamp flash code diagnosis, you can
read current code and check if history code exists, but
cannot clear the code or read history code. To enable
SRS warning lamp flash code diagnosis, short the diag-
nosis connector terminals No. 4 with No. 13, and turn
the starter switch to “ON”.
SRS control unit displays trouble code by blinking “SRS”
warning lamp. Before starting blinking mode, it makes
the initial lamp off for 1.2 seconds and blinks code “12”.
The period of lamp ON and OFF is 0.4 second each, and
there is a 1.2-second interval between tens digit and
ones digit, and 3.2-second interval between codes. If
more than one trouble code are stored, each code is dis-
played one by one. After all the codes are displayed,
they are repeatedly displayed until short circuit is dis-
connected between diagnosis connector terminals 4
and 13. There are two special codes (code 12 and code
13) in the warning lamp flash code mode. “Code 12” in-

dicates it is in flash display mode. If neither current code
nor history code is stored, SRS control unit displays
code 12 repeatedly until the connection is removed in
the diagnosis connector terminal.
“Code 13” is displayed when history code is detected or
when history code is detected but no longer appears as
current code. Tech 2 is necessary to read history codes.
Normally, keep the diagnosis connector terminals No. 4
and No. 13 disconnected.

If trouble code stored
After displaying the code 12 for three times, the stored
trouble code will be displayed for three times.
If more than one trouble code are stored, they are dis-
played in the ascending order for three times each.
After taking a round, codes are repeatedly displayed
starting with code 12. This will last as long as the self-
diagnosis connector terminal is kept shorted.

Ex.) Display start code 12

Display start

Unit = sec.

Lamp ON

Lamp OFF

Ex.) Fault code 21

0.4

3.2

1.2

Display start

Unit = sec.

Lamp ON

Lamp OFF

0.4

3.2

1.2

Ex. 1 : If no trouble code stored

Displays endlessly

Ex. 2 : If trouble codes 21 and 24 stored

Displays endlessly

N9A0068E

9C-14 SRS CONTROL SYSTEM

How to clear trouble code
Trouble codes can be cleared only with Tech 2. Howev-
er, in case DTC 25, 51, 52, 53 or 71 occurs, memory
clear cannot be performed. In this occasion, SRS control
unit must be replaced.

“Lamp OFF function when replacing SRS control unit”
A function is installed to the system that the lamp will not
turn off unless manually turned off using Tech 2 upon
completion of all inspection when replacing SRS control
unit. By communicating by following the instruction on
the display panel in Tech 2, the lamp goes off.
This function allows to confirm if checks are completed.
SRS control unit without this function is also available.

Inspection Standards for SRS airbag system repair

Description

Standard

Standard for parts replacement

In case of

collision

In case of

trouble/

periodical

inspection

SRS

parts

SRS airbag

❍

• SRS airbag had been deployed by collision.
• Pad surface is scratched or cracked.
• Connector is chapped or chipped.
• Harness is disconnected or wire is exposed.

SRS control unit

❍

• SRS airbag had been deployed by collision.
• SRS control unit body is chapped, cracked, or

deformed.

• Connector is chapped or chipped.
• Result of trouble diagnosis in the service manual

indicates to replace SRS control unit.

• Water attached to connector adjacent area.

SRS coil

❍

• SRS airbag had been deployed.
• Case body or bracket is chapped, cracked, or de-

formed.

• Result of trouble diagnosis in the service manual

indicates to replace parts.

SRS harness

❍

• Wiring harness in the SRS airbag circuit is open

or wire is exposed.

• Connector is chapped or chipped.
• Result of trouble diagnosis in the service manual

indicates to replace parts.

• Wheel is out of round.

Steering wheel

❍

• Bracket is deformed.
• New SRS airbag cannot be installed without

strain.

• When new SRS airbag is installed, pad interferes

with steering wheel, or clearance is not uniform.

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