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Home >> Mitsubishi >> 2006 >> Lancer Evolution L4-2.0L DOHC Turbo >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> Air Bag Systems >> DTC 21

DTC 21

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

Driver's Air Bag Module (Squib) Circuit:






CIRCUIT OPERATION
- The SRS-ECU judges how severe a collision is by detecting signals from the front air bag analog G-sensor. If the impact is over a predetermined level, the SRS-ECU outputs 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 input 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). The most likely causes for this code to be set are the following:
- Short circuit in driver's air bag module (squib) or harness
- Short circuit in the clock spring.

However, if no DTC reset, the SRS warning light will be switched off (DTC will be retained).

TROUBLESHOOTING HINTS
- Improper engaged connector or defective short spring*
- Short circuit in the clock spring
- Short circuit between the driver's air bag module (squib) circuit terminals
- Damaged connector(s)
- Malfunction of the SRS-ECU

NOTE: *: The squib circuit connectors integrate a "short" spring (which prevents the air bag from deploying unintentionally due to static electricity by shorting the positive wire to the ground wire in the squib circuit when the connectors are disconnected). Therefore, if connector C-12, C-205or C-201 is damaged or improperly engaged, the short spring may not be released when the connector is connected.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991911: M.U.T.-III Main Harness B
- MB991865: Dummy resister
- MB991866: Resister harness

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

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.




1. Turn the ignition switch to the "ON" position.
2. Check if the DTC is set.
3. Turn the ignition switch to the "LOOK (OFF)" position.

Q: Is DTC 34 set?

YES : Go to Step 2.

NO : Go to Step 3.




STEP 2. Check SRS-ECU connector C-12.

Q: Is the connector correctly engaged?


YES: Go to Step 3.

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

STEP 3. Check SRS-ECU connector C-12, clock spring connector C-205 and driver's air bag module connector C-201 (Using scan tool MB991958, read the diagnostic trouble code).







1. Disconnect the negative battery terminal.
2. Disconnect connectors C-12, C-205 and C-201, and then reconnect them.
3. Connect the negative battery terminal.
4. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

Q: Is DTC 21 set?

YES: Go to Step 4.

NO: The procedure is complete. It is assumed that DTC 21 set as connector C-12, C-205 or C-201 was engaged improperly.

STEP 4. Check the driver's air bag module (Using scan tool MB991958, read the diagnostic trouble code).




1. Disconnect the negative battery terminal.
2. By sliding the A section (in the figure) of air bag module connector C-201 in the arrow direction, disconnect the connector.




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 side air bag module connector C-201 by backprobing.
5. Connect the negative battery terminal.
6. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

Q: Is DTC 21 set?

YES: Go to Step 5.

NO: Replace the driver's air bag module. Then go to Step 8.

STEP 5. 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-205.
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-205 (terminal No.3 and 4) by backprobing.
5. Connect the negative battery terminal.
6. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

Q: Is DTC 21 set?

YES: Go to Step 6.

NO: Replace the clock spring. Then go to Step 8.

STEP 6. Check the driver's air bag module circuit at the SRS-ECU connector C-12.




1. Disconnect SRS-ECU connector C-12.


DANGER: To prevent the air bag from deploying unintentionally, disconnect the clock spring connector C-205 to short the squib circuit.




2. Disconnect the clock spring connector C-205.

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 terminals 11,12 and the short spring to release the short spring.

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 C-12 harness connector terminals 11 and 12. It should be open circuit.

Q: Does continuity exist?

YES: Go to Step 7.

NO: Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC 21 set, replace the SRS-ECU. Then go to Step 8.







STEP 7. Check the harness for short circuit between SRS-ECU connector C-12 (terminal No.11 and 12) and clock spring connector C-205 (terminal No.3 and 4).

Q: Are harness wires between SRS-ECU connector C-12 (terminal No.11 and 12) and clock spring connector C-205 (terminal No.3 and 4) in good condition?

YES: Go to Step 8.

NO: Repair the harness wires between SRS-ECU connector C-12 and clock spring connector C-205. Then go to Step 8.

STEP 8. Recheck for diagnostic trouble code (Using scan tool MB991958, read the 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 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 How to Use Troubleshooting/INSPECTION Service Points - How to Cope with Intermittent Malfunction).
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