Mitsubishi Lancer Evolution 8. Manual - part 110

SRS AIRBAGS – TROUBLESHOOTING

52B-5

3. SRS System Circuit Diagram 

Ignition switch (IG1)

J/B (fuse)

Backup

capacitor

DC-DC

converter

Electrical

circuit

Combination
meter

Safing G sensor

Warning

light drive

circuit

Clock spring

Driver’s
airbag
module
(squib)

Squib

detection

circuit

Squib

detection

circuit

Front
passenger’s
seat airbag
module
(squib)

Squib

detection

circuit

Squib

detection

circuit

Micro-

computer

MUT-II/III

interface

circuit

Diagnosis
connector

Driver’s
seat belt
pre-
tensioner

Squib

detection

circuit

Squib

detection

circuit

Connector

lock

detection

circuit

Front
passenger’s
seat belt
pre-
tensioner

Squib

detection

circuit

Squib

detection

circuit

Connector

lock

detection

circuit

Front impact
sensor
(vehicles not
fitted with
front
passenger’s
seat airbag)

Front G
sensor
interface
circuit

Analogue
G sensor

Remarks : *Connector lock switch 
(Connector engaged: ON 
Connector disengaged: OFF)

SRS-ECU connector

SRS AIRBAGS – TROUBLESHOOTING

52B-6

4. Chart of Diagnosis Codes

Remarks 

1. *

1

: When system reverts to normal, diagnosis code will remain stored in diagnosis code memory when the SRS warning

light switches off.

2. *

2

: When system reverts to normal, diagnosis code will be automatically erased when the SRS warning light switches off.

Code No.

Diagnostic Item

Page

1A

Front impact sensor LH system

Shorting between sensor
terminals

52B-7

1B

Front impact sensor LH system

Disconnection of sensor circuit

1C

Front impact sensor LH system

Shorting of power supply to
sensor circuit

1D

Front impact sensor LH system

Shorting of earth to sensor
circuit

2A

Front impact sensor RH system

Shorting between sensor
terminals

2B

Front impact sensor RH system

Disconnection of sensor circuit

2C

Front impact sensor RH system

Shorting of power supply to
sensor circuit

2D

Front impact sensor RH system

Shorting of earth to sensor
circuit

21

*1

Driver’s airbag module (squib) system

Shorting between terminals of
squib circuit

52B-8

22

*1

Driver’s airbag module (squib) system

Disconnection of squib circuit

52B-12

26

*1

Driver seat belt pre-tensioner (squib) system

Shorting between terminals of
squib circuit

52B-15

27

*1

Driver seat belt pre-tensioner (squib) system

Disconnection of squib circuit

52B-17

28

*1

Front passenger's seat belt pre-tensioner (squib)
system

Shorting between terminals of
squib circuit

52B-18

29

*1

Front passenger's seat belt pre-tensioner (squib)
system

Disconnection of squib circuit

52B-20

39

All airbags deployed

52B-21

46

*2

SRS-ECU assembled incorrectly

52B-21

61

Driver’s airbag module (squib) system

Short-circuited to power supply

52B-22

62

Driver’s airbag module (squib) system

Short-circuited to earth

52B-22

66

Driver seat belt pre-tensioner (squib) system

Short-circuited to power supply

52B-25

67

Driver seat belt pre-tensioner (squib) system

Short-circuited to earth

52B-25

68

Front passenger's seat belt pre-tensioner (squib)
system

Short-circuited to power supply

52B-26

69

Front passenger's seat belt pre-tensioner (squib)
system

Short-circuited to earth

52B-26

SRS AIRBAGS – TROUBLESHOOTING

52B-7

5. Inspection Procedure Classified by Diagnosis Code

Table 1

Check the front impact sensor (see p.52B-31)

Measure with C-125 SRS-ECU connector 
• Detach the connector and measure at  the harness side
• Resistance between 1 – 2 and 3 – 4
NG: 2Ω or less (short circuit) or 2MΩ or above
(disconnection)
• Connectivity between 1, 2, 3, 4 and body earth
OK: No connectivity
• Voltage between 1, 2, 3, 4 – body earth
OK: 0V

Replace the SRS-ECU 

Check connectors: A-52, A-53, C-31, C-125

Check the harness between the front impact sensor and
the SRS-ECU, and repair

Check the fault symptoms

Code No. 1A, 1B, 1C, 1D, 2A, 2B, 2C, 2D  Front impact sensor system Possible cause

These codes are output whenever the resistance between the input
terminals of the front impact sensors of the SRS-ECU differs from the
normal value. 
Refer to the table below for the fault cause for each code number.

• Harness, contactor malfunction
• Front impact senor malfunction
• SRS-ECU malfunction

Code No.

Cause of fault

1A

Shorting of left-side front impact sensor or harness short-circuit

1B

Disconnection of left-wide front impact sensor or disconnection of harness

1C

Harness of left-side front impact sensor shorted to power supply

1D

Harness of left-side front impact sensor shorted to vehicle earth

2A

Shorting of right-side front impact sensor or harness short-circuit

2B

Disconnection of right-wide front impact sensor or disconnection of harness

2C

Harness of right-side front impact sensor shorted to power supply

2B

Harness of right-side front impact sensor shorted to vehicle earth

OK

OK

NG

OK

NG

NG

Repair

SRS AIRBAGS – TROUBLESHOOTING

52B-8

Remarks:

*The connector of the squib circuit contains a short bar (which shorts the (+) cable to the (–) cable of the squib circuit when

the connector is not connected, in order to avoid erroneous deployment due to static electricity, or the like). Therefore, when
a connector is connected, the short bar may not be released if there is a fault in the connector fitting or a malfunction in the
connector itself, as illustrated below. Before proceeding to the troubleshooting steps on the next page, disconnect the
connector as shown below, and then reconnect it. If no diagnosis code is output, then it can be assumed that the code was
previously output due to poor fitting of the connector.

Code No. 21 Driver’s airbag module (squib) system

Possible cause

This code is output when shorting occurs between the terminals of the
driver’s airbag module (squib) circuit of the SRS-ECU. 
When normal operation is resumed, the SRS warning light goes out. (The
diagnosis code is not erased.)

• Fault in the connector fitting or fault in the short

bar*

• Shorting in the clock spring
• Shorting between the terminals of the driver’s

airbag module (squib) circuit

• Connector fault
• SRS-ECU fault

Type 1

Clock spring

Clock spring

Driver’s airbag module

Driver’s airbag module

AC105785

AC105787AB

Type 2