Mitsubishi Evolution X. Manual - part 649

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-43

CIRCUIT OPERATION

• The SRS-ECU judges how severe a collision is 

by detecting signals from the front impact sensors 
and the front air bag analog G-sensor. If the 
impact is over a predetermined level, the 
SRS-ECU sends an ignition signal. At this time, if 
the front air bag safing G-sensor is on, the SRS 
air bag will inflate. 

• The ignition signal is sent to the air bag module 

via the clock spring to inflate the air bag.

.

DTC SET CONDITIONS

This DTC is set if there is abnormal resistance 
between the input terminals of the driver's air bag 
module (squib).

.

TROUBLESHOOTING HINTS

• Malfunction of the clock spring

• Damaged harness wires and connectors

• Short to the ground in the driver's air bag module 

(squib) harness

• Malfunction of the SRS-ECU

DIAGNOSIS

Required Special Tools:

• MB991958: Scan Tool (M.U.T.-III Sub Assembly)

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827: M.U.T.-III USB Cable

• MB991910: M.U.T.-III Main Harness A (Vehicles with 

CAN Communication System)

• MB991865: Dummy resistor

• MB991866: Resister harness

STEP 1. Using scan tool MB991958, diagnose the CAN bus 
line.

CAUTION

To prevent damage to scan tool MB991958, always turn the 
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958. Refer to "How to connect the 

scan tool 

P.52B-28

."

(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.
NO :  Repair the CAN bus line (Refer to GROUP 54C, 

Diagnosis 

P.54C-14

).

AC608435

Data link connector

MB991827

MB991824

MB991910

AB

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-44

STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?

YES : Go to Step 3.
NO :  There is an intermittent malfunction such as poor 

engaged connector(s) or open circuit (Refer to 
GROUP 00, How to Cope with Intermittent 
Malfunction 

P.00-15

).

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-45

STEP 3. Check the driver's air bag module.
(1) Disconnect the negative battery terminal.
(2) Slide the outer housing of the driver’ s air bag module 

connector C-204 in the arrow direction shown, and 
disconnect the connector.

(3) Connect special tool MB991865 to special tool MB991866.

CAUTION

Do not insert a probe into the terminal from its front side 
directly, as the connector contact pressure may be weak-
ened.
(4) Insert special tool MB991866 into clock spring side air bag 

module connector C-204 (terminal No.1 and 2 <1st squib> 
or terminal No.3 and 4 <2nd squib>) by backprobing.

(5) Connect the negative battery terminal.

CAUTION

Always DTC B1B06 is set when checking DTC B1B00. This 
is because the second side terminal is isolated when 
checking it, DTC B1B06 is set but this is not a fault. In 
addition, always DTC B1B02 is set when checking DTC 
B1B04 because the first side terminal is isolated. 
(6) Erase the diagnostic trouble code memory, and check the 

diagnostic trouble code.

Q: Is the checked DTC set?

YES : Go to Step 4.
NO :  Replace the driver's air bag module (Refer to 

P.52B-386

). Then go to Step 7. 

AC605948

AC600868

AF

Outer housing of the driver's air bag 
module connector

Driver's air bag module 
Connector (4 pin yellow)

Horn connector

Lower column 
cover

AC306758AY

MB991865 
(Dummy resistor: 3   )

MB991866 
(Resistor harness)

C-204 Air bag 
module connector

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-46

STEP 4. Check the clock spring.
(1) Disconnect the negative battery terminal.
(2) Disconnect the clock spring connector C-208.
(3) Connect special tool MB991865 to special tool MB991866.

CAUTION

Do not insert a test probe into the terminal from its front 
side directly, as the connector contact pressure may be 
weakened.
(4) Insert special tool MB991866 into clock spring harness side 

connector C-208 (terminal No. 3 and 4 <1st squib> or 
terminal No. 2 and 1 <2nd squib>) by backprobing.

(5) Connect the negative battery terminal.

CAUTION

Always DTC B1B06 is set when checking DTC B1B00. This 
is because the second side terminal is isolated when 
checking it, DTC B1B06 is set but this is not a fault. In 
addition, always DTC B1B02 is set when checking DTC 
B1B04 because the first side terminal is isolated. 
(6) Erase the diagnostic trouble code memory, and check the 

diagnostic trouble code.

Q: Is the checked DTC set?

YES : Go to Step 5.
NO :  Replace the clock spring (Refer to 

P.52B-386

). Then 

go to Step 7. 

AC306767

C-208 Clock spring
connector

AR

MB991865 
(Dummy resistor: 3   )

MB991866 
(Resistor harness)