DTC 42

IG1 Power Circuit System (Fuse No.3 Circuit)

IG1 Power Circuit System (Fuse No.3 Circuit):

Connectors:

CIRCUIT OPERATION
- The SRS-ECU is powered from the ignition switch (IG1).
- The SRS-ECU power is supplied from two circuits. Even if one circuit is shut off, the air bag can inflate.

DTC SET CONDITIONS
- These DTC are output if the voltage between the IG1 terminals (fuse No.3 circuit) and ground is lower than a predetermined value for a continuous period of five second or more. However, if the vehicle condition returns to normal, DTC numbers 42 will be automatically erased, and the SRS warning light will switch off.

TROUBLESHOOTING HINTS
- Damaged wiring harnesses or connectors
- Malfunction of the SRS-ECU

DIAGNOSIS

Required Special Tools:
- MB991502: Scan Tool (MUT-II)
- MB991223 (MB991222): Harness set (Probe)

STEP 1. Check junction block multi-purpose fuse number 3.

Q: Is the fuse burned out?

NO: Go to Step 2.
YES: Go to Step 4.







STEP 2. Check the harness for open circuit between the SRS-ECU and the ignition switch (IG1).
Measurement at SRS-ECU connector C-12.
1. Disconnect SRS-ECU connector C-12.
2. Connect the negative battery terminal.
3. Turn the ignition switch to the "ON" position.

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

4. Measure at the wiring harness side.
5. Measure the voltage between terminal 13 and body ground
- Voltage should be 9 volts or more.

Q: Is the voltage normal?

YES: Erase the DTC memory, and recheck if any DTC sets. If DTC 42 sets, replace the SRS-ECU. Then go to Step 8.
NO: Go to Step 3.







STEP 3. Check the harness for open circuit between SRS- ECU connector C-12 and the ignition switch (IG1).

NOTE: After inspecting intermediate connectors C-214 and C-211, inspect the wiring harness. If intermediate connectors are damaged, repair or replace them. Refer to Harness Connector Inspection. Then go to Step 8.

Q: Are harness wires between SRS-ECU connector C-12 and the ignition switch (IG1) in good condition?

YES: Go to Step 8.
NO: Repair the harness wires between SRS-ECU connector C-12 and the ignition switch (IG1). Then go to Step 8.

STEP 4. Check a burned-out fuse.
1. Replace the fuse.
2. Turn the ignition switch to the "ON" position, wait for at least one minute and then turn the switch off.
3. Check the fuse.

Q: Is the fuse in good condition?

YES: Go to Step 8.
NO: Go to Step 5.




STEP 5. Check the harness for short circuit to ground between the SRS-ECU and the junction block.
1. Measure at junction block connector C-214.
2. Disconnect junction block connector C-214, and 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.




3. Check the continuity between terminals 7 and body ground. There should be open circuit.

Q: Is the continuity normal?

YES: Check the other circuit, which flows through multipurpose fuse number 3.
NO: Go to Step 6.




STEP 6. Check the harness for short circuit to ground between the SRS-ECU and the junction block
1. Disconnect SRS-ECU connector C-12, and 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.




2. Check the continuity between terminals 13 and body ground.
- There should be open circuit.

Q: Is the continuity normal?

YES: Erase the DTC memory, and recheck if any DTC sets. If DTC 42 sets, replace the SRS-ECU. Then go to step 8.
NO: Go to Step 7.







STEP 7. Check the harness wires between SRS-ECU connector C-12 and junction block connector C-214.

Q: Are harness wires between SRS-ECU connector C-12 and junction block connector C-214 in good condition?

YES: Go to Step 8.
NO: Repair the harness wires between SRS-ECU connector C-12 and junction block connector C-214. Then go to Step 8.

STEP 8. Check for DTC.

Q: Is DTC 42 output?

YES: Replace the SRS-ECU.
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.)