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
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