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

WARNING: This page is about a different car, the 2005 Dodge Stratus and 2005 Chrysler Sebring. However, it is still accessible from the selected car via links, so may be relevant.

Required Special Tools:

MB991502: Scan Tool (MUT-II)
MB991613: SRS Check Harness
MB991865: Dummy Resistor
MB991866: Resistor Harness
MB991223 (MB991222): Harness Set (Probe)

STEP 1. Check the DTC.
Q: Is DTC 34 set?

YES : Go to Step 2.

NO: Go to Step 3.
STEP 2. Check the SRS-ECU connector C-137.
Q: Is the connector correctly engaged?

YES : Go to Step 3.

NO: Engage the connector correctly. Then go to Step 8.

Fig 1: Identifying Connector C-137
Courtesy of DAIMLERCHRYSLER CORPORATION
STEP 3. Check the SRS-ECU connector C-137, the clock spring connector C-204 and the driver's air bag module connector C-208.
1. Disconnect the negative battery terminal.
2. Disconnect the connectors C-137, C-204 and C-208, and then reconnect them.
  
  Fig 2: Identifying Connector C-137
  Courtesy of DAIMLERCHRYSLER CORPORATION
  
  Fig 3: Identifying Connectors C-204, C-208
  Courtesy of DAIMLERCHRYSLER CORPORATION
  
  NOTE: For the driver's air bag module connector C-208, there should be no gap at the place B. See Fig 4.
  
  Fig 4: Identifying Driver Air Bag Module Connector C-208
  Courtesy of DAIMLERCHRYSLER CORPORATION
3. Connect the negative battery terminal.
4. Erase the DTC memory, and then check the DTC.
Q: Is DTC 21 set?

YES : Go to Step 4.

NO: The procedure is complete. It is assumed that DTC 21 set as the connector C-137, C-204 or C-208 was engaged improperly.
STEP 4. Check the SRS-ECU to clock spring line.
1. Disconnect the negative battery terminal.
2. Release the clock spring connector C-204 (4-pin).
  
  Fig 5: Identifying Clock Spring Connector C-204 (4-Pin)
  Courtesy of DAIMLERCHRYSLER CORPORATION
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 the clock spring harness side connector C-204 (terminal No. 3 and 4) by backprobing.
5. Connect the negative battery terminal.
6. Erase the DTC memory, and then recheck the DTC.
  
  Fig 6: Identifying Special Tools
  Courtesy of DAIMLERCHRYSLER CORPORATION
Q: Is DTC 21 set?

YES : Go to Step 6.

NO: Go to Step 5.
STEP 5. Check the clock spring and the driver's air bag module.
1. Disconnect the negative battery terminal.
2. Connect connector (4) of special tool MB991613 to clock spring connector C-208.
3. Connect connector (1) of special tool MB991613 to connector (2).
4. Connect terminals 22 to 24, and terminals 23 to 25 of special tool MB991613 to connector (5).
5. Connect the clock spring to the instrument panel wiring harness.
6. Connect the negative battery terminal.
7. Erase the DTC memory, and then recheck the DTC.
Q: Is DTC 21 set?

YES : Replace the clock spring (Refer to AIR BAG MODULES AND CLOCK SPRING ). Then go to Step 8.

NO: Replace the driver's air bag module (Refer to AIR BAG MODULES AND CLOCK SPRING ). Then go to Step 8.

Fig 7: Connecting Clock Spring To Instrument Panel Wiring Harness
Courtesy of DAIMLERCHRYSLER CORPORATION
STEP 6. Check the driver's air bag module circuit at the SRS-ECU connector C-137.
1. Disconnect the SRS-ECU connector C-137.
  
  Fig 8: Identifying SRS-ECU Connector C-137
  Courtesy of DAIMLERCHRYSLER CORPORATION
  
  WARNING: To prevent the air bag from deploying unintentionally, disconnect the clock spring connector C-204 to short the squib circuit.
2. Disconnect the clock spring connector C-204.
  
  Fig 9: Identifying Clock Spring Connector C-204
  Courtesy of DAIMLERCHRYSLER CORPORATION
  
  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 be released.
3. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between the terminals 7, 8 and the short spring to release the short spring.
  
  Fig 10: Inserting Cable Tie Between Clock Spring Connector Terminals
  Courtesy of DAIMLERCHRYSLER CORPORATION
  
  CAUTION: Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
4. Check for continuity between the C-137 harness side connector terminals 7 and 8.
  It should be open circuit.
Q: Does continuity exist?

YES : Go to Step 7.

NO: Erase the DTC memory, and recheck if any DTC sets. If DTC 21 sets, replace the SRS-ECU (Refer to SRS CONTROL UNIT (SRS-ECU) ). Then go to Step 8.

Fig 11: Checking Continuity Between C-137 Harness Side Connector Terminals
Courtesy of DAIMLERCHRYSLER CORPORATION
STEP 7. Check the harness wires for short circuit between the SRS-ECU connector C-137 (terminal No.7 and 8) and the clock spring connector C-204 (terminal No.3 and 4).
Q: Are the harness wires between the SRS-ECU connector C-137 (terminal No.7 and 8) and the clock spring connector C-204 (terminal No.3 and 4) in good condition?

YES : Go to Step 8.

NO: Repair the harness wires between the SRS-ECU connector C-137 and the clock spring connector C-204. Then go to Step 8.

Fig 12: Identifying SRS-ECU Connector C-137
Courtesy of DAIMLERCHRYSLER CORPORATION

Fig 13: Identifying Clock Spring Connector C-204
Courtesy of DAIMLERCHRYSLER CORPORATION
STEP 8. Check the DTC.
Q: Is DTC 21 set?

YES : Return to Step 1.

NO: The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected Refer to TO COPE WITH INTERMITTENT MALFUNCTION ).