DTC 21: Driver's Air Bag Module (Squib) System Fault 1 (Short Circut between Terminal of the Squib Circuit): Diagnosis

Required Special Tools:

MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicle Communication Interface
- MB991827: MUT-III USB Cable
- MB991911: MUT-III Main Harness B
MB991613: SRS Check Harness
MB991865: Dummy resister
MB991866: Resister harness

STEP 1. Using scan tool MB991958, read the diagnostic trouble code.

Fig 1: Connecting Special Tool MB991911 To Data Link Connector
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Q: Is DTC 34 output?
1. YES: Go to Step 2.
2. NO: Go to Step 3.
STEP 2. Check the SRS-ECU connector C-72.

Fig 2: Identifying SRS-ECU C-72 Connector Terminal
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Q: Is the connector correctly engaged?
1. YES: Go to Step 3.
2. NO: Engage the connector correctly. Then go to Step 9.
STEP 3. Check the air bag module connector C-81.
Remove the air bag module mounting equipment and check air bag module connector C-81. At this time, check that there is no gap at place B shown in the illustration (Refer to INSPECTION ).

Fig 3: Identifying Air Bag Module Connector C-81
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Q: Is the connector correctly connected?
1. YES: Go to Step 4.
2. NO: Insert the connector to the place, where there remains no gap at place B shown in the illustration. Then go to Step 9.
STEP 4. Check the SRS-ECU connector C-72 and clock spring connector C-85 (Using scan tool MB991958, read the diagnostic trouble code).
1. Disconnect the negative battery terminal.
2. Disconnection connectors C-72 and C-85 then reconnect them.
  
  Fig 4: Identifying SRS-ECU Connector C-72
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  
  Fig 5: Identifying Clock Spring Connector C-85
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. Connect the negative battery terminal.
4. Erase the DTC memory, and then check the DTC.
Q: Is DTC 21 output?
1. YES: Go to Step 5.
2. NO: The procedure is complete (It is assumed that DTC 21 set as connector C-72 or C-85 was engaged improperly).
STEP 5. Check the driver's air bag module line (Using scan tool MB991958, read the diagnostic trouble code).
1. Disconnect the negative battery terminal.
2. Remove the driver's air bag module (Refer to INSPECTION ).
3. Connect connector (4) of special tool MB991613 to clock spring connector C-81.
  
  Fig 6: Checking Driver's Air Bag Module Line
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. Connect connector (1) of special tool MB991613 to connector (2).
5. Connect terminals 22 to 24, and terminals 23 to 25 of special tool MB991613 to connector (5).
6. Connect the clock spring to the body wiring harness.
7. Connect the negative battery terminal.
8. Erase the DTC memory, and then recheck the DTC.
Q: Is DTC 21 output?
1. YES: Go to Step 6.
2. NO: Replace the driver's air bag module. Refer to INSPECTION . Then go to Step 9.
STEP 6. Check the clock spring (Using scan tool MB991958, read the diagnostic trouble code).
1. Disconnect the negative battery terminal.
2. Disconnect the clock spring connector C-85.
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-85 (terminal No. 3 and 4) by backprobing.
  
  Fig 7: Inserting Special Tool MB991866 Into Clock Spring Harness Side Connector C-85
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
5. Connect the negative battery terminal.
6. Erase the DTC memory, and then recheck the DTC.
Q: Is DTC 21 output?
1. YES: Go to Step 7.
2. NO: Replace the clock spring. Refer to INSPECTION . Then go to Step 9.
STEP 7. Check harness between the SRS-ECU and the clock spring for short circuit.
1. Disconnect SRS-ECU connector C-72.
  
  Fig 8: Identifying SRS-ECU C-72 Connector Terminal
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  
  CAUTION: To release the short bar in the SRS-ECU connector, disconnect connector C-85 to short the squib circuit.
2. Disconnect the clock spring connector C-85.
  
  Fig 9: Identifying Clock Spring C-85 Connector Terminal
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  
  CAUTION: Insert an insulator such as a cable tie to a depth of 4mm (0.16 inch) or more, otherwise the short spring will not cable tie release.
3. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 7, 8 and the short spring to release the short spring.
  
  Fig 10: Inserting Cable Tie Between Terminals 7, 8
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. Measure at the wiring harness side.
  CAUTION: Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
5. Check for continuity between terminals 7 and 8.
  - There should be open circuit.
Q: Does continuity exist?
1. YES: Go to Step 8.
2. NO: Erase the DTC memory, and recheck if any DTC sets. If DTC 21 sets, replace the SRS-ECU. Refer to HARNESS CONNECTOR . Then go to Step 9.
STEP 8. Check the harness for short circuit between SRS-ECU connector C-72 (terminal No. 7 and 8) and clock spring connector C-85 (terminal No. 3 and 4).

Fig 12: Checking Harness Short Circuit Between SRS-ECU Connector C-72 (Terminal No. 7 And 8)
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Fig 13: Checking Clock Spring Connector C-85 (Terminal No. 3 And 4)
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Q: Are harness wires between SRS-ECU connector C-72 (terminal No. 7 and 8) and clock spring connector C-85 (terminal No. 3 and 4) in good condition?
1. YES: Go to Step 9.
2. NO: Repair the harness wires between SRS-ECU connector C-72 and clock spring connector C-85. Then go to Step 9.
STEP 9. Recheck for diagnostic trouble code.
Q: Is DTC 21 output?
1. YES: Return to Step 1.
2. NO: The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ).