Code No. C1861: Power
supply low voltage
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- If there is any
problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis,
diagnose the CAN bus lines (Refer to GROUP 54C -
CAN Bus Diagnostics Table
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- Whenever ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out
the calibration of the G and yaw rate sensor and the steering wheel sensor (Refer to and ).
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OPERATION
The ASC-ECU is energised by the ignition switch through the multi-purpose fuse at the
terminal IG1.
DIAGNOSIS CODE SET CONDITIONS
The ASC-ECU monitors the ASC-ECU power supply voltage sent from the battery. When the
voltage falls below a predetermined value, the ECU determines that the trouble occurs and sets
the diagnosis code.
PROBABLE CAUSES
Current trouble
- Battery failure.
- Charging system failed.
- Damaged harness wires and connectors.
- Malfunction of the hydraulic unit assembly (integrated with ASC-ECU).
Past trouble
- Carry out diagnosis with particular emphasis on connector(s) or wiring harness in
the power supply circuit (+BV and IG1 terminals) to the ASC-ECU. For diagnosis procedures,
refer to How to treat past trouble. (GROUP 00 -
How to Use Troubleshooting/Inspection
Service Points).
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STEP 1. M.U.T.-III CAN bus diagnosis.
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Use the M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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 Go to Step 3.
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 Repair the CAN bus line. (Refer to GROUP 54C -
Troubleshooting ).
On completion, go to Step 2.
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STEP 2. Diagnosis code recheck after resetting CAN bus lines.
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Q.
Is diagnosis code No. C1861 set?
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Go to Step 3.
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This diagnosis is complete.
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STEP 3. Check the battery.
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Refer to GROUP 54A -
Battery Test .
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Q.
Is the battery in good condition?
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Go to Step 4.
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Charge or replace the battery (Refer to GROUP 54A -
Battery . Then
go to Step 11.
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STEP 4. Check the charging system.
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Refer to GROUP 16 -
Charging System, On-vehicle Service.
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Q.
Is the charging system in good condition?
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Go to Step 5.
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Repair or replace the charging system component(s). Then go to Step 11.
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STEP 5. Measure the resistance at the ASC-ECU connector.
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(1)Connector check: the hydraulic unit assembly (integrated with ASC-ECU), the fuses
(relay box) and the fusible links.
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(2)Disconnect the hydraulic unit assembly (integrated with ASC-ECU) connector.
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(3)Measure the resistance between +BV terminal and body earth.
OK: No continuity
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Q.
Is the check result normal?
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Go to Step 6.
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The power supply circuit may be short. Repair the wiring harness wires or connectors
between the hydraulic unit assembly (integrated with ASC-ECU) connector +BV terminal
and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 11.
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STEP 6. Measure the resistance at the ASC-ECU connector.
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(1)Connector check: the hydraulic unit assembly (integrated with ASC-ECU) connector
and the junction block.
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(2)Disconnect the hydraulic unit assembly (integrated with ASC-ECU) connector.
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(3)Measure the resistance between the IG1 terminal and body earth.
OK: No continuity
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Q.
Is the check result normal?
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Go to Step 7.
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The power supply circuit may be short. Repair the wiring harness wires or connectors
between the hydraulic unit assembly (integrated with ASC-ECU) connector IG1 terminal and the
junction block. Then go to Step 11.
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STEP 7. Measure the voltage at the ASC-ECU connector.
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(1)Disconnect the hydraulic unit assembly (integrated with ASC-ECU) connector.
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(2)Measure the voltage between +BV terminal and body earth.
OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 8.
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The power supply circuit may be open. Repair the wiring harness wires or connectors
between the hydraulic unit assembly (integrated with ASC-ECU) connector +BV terminal
and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 11.
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STEP 8. Measure the voltage at the ASC-ECU connector.
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(1)Disconnect the hydraulic unit assembly (integrated with ASC-ECU) connector.
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(3)Measure the voltage between the IG1 terminal and body earth.
OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 9.
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The power supply circuit may be open. Repair the wiring harness wires or connectors
between the hydraulic unit assembly (integrated with ASC-ECU) connector IG1 terminal and the
junction block. Then go to Step 11.
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STEP 9. Measure the resistance at the ASC-ECU connector.
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(1)Disconnect the hydraulic unit assembly (integrated with ASC-ECU) connector.
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(2) Measure the resistance between the GND1 terminal and body earth as well as between
the GND2 terminal and body earth.
OK: Continuity exists (2 Ω
or less).
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Q.
Is the check result normal?
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Go to Step 10.
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The earth circuit may be open. Repair the wiring harness wires or connectors between
the hydraulic unit assembly (integrated with ASC-ECU) connector GND1 terminal and the fusible
links as well as between the GND2 terminal and the fusible links. Then go to Step 11.
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STEP 10. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set.
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(1)Erase the set diagnosis code.
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(2)Ignition switch: "LOCK" (OFF)
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Q.
Is diagnosis code No. C1861 set?
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Replace the hydraulic unit assembly (integrated with ASC-ECU) (Refer to ).
Then go to Step 11.
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The trouble can be an intermittent malfunction. (Refer to GROUP 00 -
How
to Cope with Intermittent Malfunction).
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STEP 11. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set.
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(1)Erase the set diagnosis code.
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(2)Ignition switch: "LOCK" (OFF)
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Q.
Is diagnosis code No. C1861 set?
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Return to Step 3.
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This diagnosis is complete.
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