DTC 24

DTC 24 : Passenger's (Front) Air Bag Module (Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit)

Passenger's Air Bag Module (Squib) Circuit:

CIRCUIT OPERATION
- The SRS-ECU judges how severe a collision is by detecting signals from the left and right side impact sensors and the analog G-sensor. If the impact is over a predetermined level, the SRS-ECU outputs an ignition signal. At this time, if the safing G-sensor is on, the SRS air bag will inflate.
- The ignition signal is input to the air bag module to inflate the air bag.

DTC SET CONDITIONS
- This DTC is set if there is abnormal resistance between the input terminals of the passenger's (front) air bag module (squib). The most likely causes for this code to be set are shown in the table below: However, if no DTC resets, the SRS warning light will be switched off (The DTC will be retained).

TROUBLESHOOTING HINTS
- Improper engaged connector or defective short spring*
- Short circuit between the passenger's (front) 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 the connector C-11 or C-72 is damaged or improperly engaged, the short spring may not be released when the connector is connected.

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
- MB991865: Dummy resister
- MB991866: Resister harness




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

Q: Is DTC 34 set?

YES: Go to Step 2.

NO: Go to Step 3.




STEP 2. Check SRS-ECU connector C-72.

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-72 and passenger's connector C-11.







1. Disconnect the negative battery terminal.
2. Disconnection connectors C-72 and C-11, and then reconnect them.
3. Connect the negative battery terminal.
4. Erase the DTC memory, and then check the DTC.

Q: Is DTC 24 set?

YES: Go to Step 4.

NO: The procedure is complete (It is assumed that DTC 24 set as connector C-72 or C-11 was engaged improperly).

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




1. Disconnect the negative battery terminal.
2. Unclip passenger's air bag module connector C-11.




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. Disconnect the passenger's air bag module connector C-11, and insert special tool MB991866 into the harness side connector by backprobing.
5. Connect the negative battery terminal.
6. Erase the DTC memory, and then recheck the DTC.

Q: Is DTC 24 output?

YES: Go to Step 5.

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-72.




2. Unclip passenger's air bag module connector C-11.

CAUTION: To release the short spring in the SRS-ECU connector, disconnect connector C-11 to short the squib circuit.

3. Disconnect the passenger's air bag module connector C-11.

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.




4. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 5, 6 and the short spring to release the short spring.
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 for continuity between terminals 5 and 6.
- There should be open circuit.

Q: Does continuity exist?

YES: Go to Step 6.

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







STEP 6. Check the harness for short circuit between SRS-ECU connector C-72 (terminal No.5 and 6) and passenger's side air bag module connector C-11 (terminal No.1 and 2).

Q: Are harness wires between SRS-ECU connector C-72 (terminal No.5 and 6) and passenger's side air bag module connector C-11 (terminal No.1 and 2) in good condition?

YES: Go to Step 7.

NO: Repair the harness wires between SRS-ECU connector C-72 and passenger's side air bag module connector C-11. Then go to Step 7.

STEP 7. Recheck for diagnostic trouble code.

Q: Is DTC 24 output?

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).