SRS Warning Light Drive Circuit System Fault 1 (Light Does Not Illuminate)

SRS Warning Light Drive Circuit System Fault 1 (Light Does Not Illuminate.)

SRS Warning Light Drive Circuit Part 1:

CIRCUIT OPERATION
- Power for the SRS warning light is supplied from the ignition switch (IG1) circuit.
- The SRS warning light illuminates when the ignition switch is turned "ON" and goes out after approximately seven seconds if there is not a malfunction in the SRS system.

DTC SET CONDITIONS
- This DTC is set when an open circuit is detected for a continuous period of five seconds while the SRS-ECU is monitoring the SRS warning light and the light is OFF. (transistor OFF.) However, if the vehicle condition returns to normal, DTC 43 will be automatically erased, and the SRS warning light will go out.

TROUBLESHOOTING HINTS
- Damaged wiring harnesses of connectors
- Blown bulb
- Malfunction of the SRS-ECU
- Malfunction of the combination meter

Required Special Tools:
- MB991502: Scan Tool (MUT-II)

STEP 1. Check the SRS warning light.

1. Connect the negative battery terminal.




2. Disconnected the SRS-ECU connector C-72.
3. Turn the ignition switch to the "ON" position.

Q: Does the warning light illuminate?

YES: Erase the DTC memory, and recheck if any DTC sets. If DTC 43 sets, replace the SRS-ECU. Then go to Step 6.

NO: Go to Step 2.

STEP 2. Check the ground line at the SRS-ECU connector C-72.







1. Disconnect SRS-ECU connector C-72.
2. Connect the negative battery terminal.

CAUTION: Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.

3. Measure the continuity between terminal 3 and ground.
- Should be less than 2 Ohms.

Q: Is the continuity normal?

YES: Go to Step 3.

NO: Then go to Step 5.




STEP 3. Check the SRS warning light bulb.

Q: Has the SRS warning light bulb blown?

YES: Replace the SRS warning light bulb. Then go to Step 6.

NO: Go to Step 4.










STEP 4. Check the harness for open circuit between SRS-ECU connector C-72 (terminal No.4) and the ignition switch (IG1).

NOTE: After inspecting intermediate connectors C-41, C-42, C-108, C-111 inspect the wiring harness. If intermediate connectors C-41, C-42, C-108, C-111 are damaged, repair or replace them. Refer to Harness Connector Inspection. Then go to Step 5.

Q: Are the harness wires between SRS-ECU connector C-72 (terminal No.4) and the ignition switch (IG1) in good condition?

YES: Replace the combination meter.

NO: Repair the harness wires between SRS-ECU connector E-08 and the ignition switch (IG1). Then go to Step 6.




STEP 5. Check the harness for open circuit between SRS-ECU connector C-72 (terminal No.3) and ground.

Q: Is the harness wire between SRS-ECU connector C-72 (terminal No.3) and ground in good condition?

YES: Go to Step 6.

NO: Repair the harness wires between SRS-ECU connector C-72 and ground. Then go to Step 6.

STEP 6. Check for DTC.

Q: Is DTC 43 output?

YES: There is no action to be taken.

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.)