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.

DTC SET CONDITIONS
This DTC is set if a short circuit is detected between the terminals of the passenger's side air bag module (squib). However, if the vehicle condition returns to normal, the SRS warning light will go out, but the 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 the connector C-12 or C-137 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 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 7.

STEP 3. Check the SRS-ECU connector C-137 and the passenger's air bag module connector C-12.







1. Disconnect the connectors C-12 and C-137, and then reconnect them.
2. Connect the negative battery terminal.
3. Erase the DTC memory, and then recheck 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 the connector C-12 or C-137 was engaged improperly.

STEP 4. Check the passenger's air bag module.




1. Disconnect the passenger's air bag module connector C-12.




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. 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 set?

YES: Go to Step 5.
NO: Replace the passenger's air bag module. Then go to Step 7.

STEP 5. Check the passenger's air bag module circuit at the SRS-ECU connector C-137.




1. Disconnect the SRS-ECU connector C-137.

DANGER: To prevent the air bag from deploying unintentionally, disconnect the passenger's air bag module connect6r C-12 to short the squib circuit.




2. Disconnect the passenger's air bag module connector C-12.

CAUTION: Insert an insulator such as a cable tie to a depth of 4mm (0.16 inch) or more, otherwise the short bar 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 9,10 and the short bar to release the short bar.

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 5 and 6.
It should be open circuit.

Q: Does continuity exist?

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 wires for short circuit between the SRS-ECU connector C-137 (terminal No.5 and 6) and the passenger's air bag module connector C-12 (terminal No.1 and 2).

Q: Are the harness wires between the SRS-ECU connector C-137 (terminal No.5 and 6) and passenger's air bag module connector C-12 (terminal No.1 and 2) in good condition?

YES: Go to Step 7.
NO: Repair the harness wires between the SRS-ECU connector C-137 and the passenger's air bag module connector C-12. Then go to Step 7.

STEP 7. Check the DTC.

Q: Is DTC 24 set?

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