DTC 24

Passenger's (Front) Air Bag Module (Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit)

Passenger's (Front) 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
- These DTC are output if there is abnormal resistance between the input terminals of the passenger's side air bag module (squib). However, if no DTC resets, the SRS warning light will be switched off (DTC will be retained).

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

NOTE: *: The squib circuit connectors integrate a "short" bar (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 or C-106 is damaged or improperly engaged, the short bar may not be released when the connector is connected.

DIAGNOSIS

Required Special Tools:
- MB991502: Scan Tool (MUT-II)
- MB991865: Dummy resister
- MB991866: Resister harness

STEP 1. Check the DTC.

Q: Is DTC 34 output?

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 7.







STEP 3. Check SRS-ECU connector C-12 and passenger's air bag module connector C-106.
1. Disconnect connectors C-12 and C-106, and then reconnect them.
2. Connect the negative battery terminal.
3. Erase the DTC memory, and then recheck the DTC.

Q: Is DTC 24 output?

YES: Go to Step 4.
NO: The inspection is complete. It is assumed that DTC 24 set as connector C-12 or C-106 was engaged improperly.







STEP 4. Check the passenger's air bag module.
1. Unclip passenger's air bag module connector C-106.
2. 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.

3. Disconnect the passenger's air bag module connector C-106, and insert special tool MB991866 into the harness side connector by backprobing.
4. Connect the negative battery terminal.
5. Erase the DTC memory, and then recheck the DTC.

Q: Is DTC 24 output?

YES: Go to Step 4.
NO: Replace the passenger's air bag module. Then go to Step 7.

STEP 5. Check the harness for short circuit between SRS-ECU and the passenger's air bag module.




1. Disconnect SRS-ECU connector C-12.




2. Unclip passenger's air bag module connector C-106.

CAUTION: To release the short bar in the SRS-ECU connector, disconnect connector C-106 to short the squib circuit

3. Disconnect the passenger's air bag module connector C-106.






CAUTION: Insert an insulator such as a cable tie to a depth of 4 mm (0.16 inch) or more, otherwise the short bar will not be released.

4. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 9,10 and the short bar to release the short bar.
5. 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.




6. Check the continuity between terminals 9 and 10.
- There should be open circuit.

Q: Is the continuity normal?

YES: Erase the DTC memory, and recheck if any DTC sets. If DTC 24 sets, replace the SRS-ECU. Then go to Step 7.
NO: Go to Step 6.







STEP 6. Check the harness for short circuit between SRS- ECU connector C-12 and passenger's air bag module connector C-106.

Q: Are harness wires between SRS-ECU connector C-12 and passenger's air bag module connector C-106 in good condition?

YES: Go to Step 7.
NO: Repair the harness wires between SRS-ECU connector C-12 and passenger's air bag module connector C-106. Then go to step 7.

STEP 7. Check the DTC.

Q: Is DTC 24 output?

YES: Return to Step 1.
NO: This diagnosis is complete. (If no malfunctions are not found in all steps, an intermittent malfunction is suspected. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction.)