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Code No. C1861 Power supply low voltage
 
 
caution
  • If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C, CAN Bus Diagnostics Table ).
  • 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 steering wheel sensor and the G and yaw rate sensor (Refer to and ).
 
 
OPERATION
The ASC-ECU is energized by the ignition switch through the multi-purpose fuse at the terminal IG1.
 
 
DIAGNOSTIC TROUBLE 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 diagnostic trouble code.
 
 
PROBABLE CAUSES
Current trouble
  • Battery failure
  • Charging system failed
  • Damaged harness wires and connectors
  • Malfunction of 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 ).
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-III), diagnose the CAN bus lines.
Use scan tool (M.U.T.-III) to diagnose the CAN bus lines.
Is the check result normal?
Go to Step 3.
Repair the CAN bus line (Refer to GROUP 54C, Troubleshooting ). On completion, go to Step 2.
 
STEP 2. Diagnostic trouble code recheck after resetting CAN bus lines
Is diagnostic trouble code No. C1861 set?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Check the battery.
Refer to GROUP 54A, Battery Test .
Is the auxiliary battery normal?
Go to Step 4.
Charge or replace the battery. Then go to Step 11.
 
STEP 4. Check the charging system.
Refer to GROUP 16, Charging System .
Is the charging system in good condition?
Go to Step 5.
Repair or replace the charging system component(s). Then go to Step 11.
 
STEP 5. Measure the resistance at the ASC-ECU connector.
(1) Connector check: the ASC-ECU connector, the fuses (relay box) and the fusible links
(2) Disconnect the ASC-ECU connector.
(3) Measure the resistance between +BV terminal and body ground.
OK: No continuity
Is the check result normal?
Go to Step 6.
The power supply circuit may be short. Repair the wiring harness wires or connectors between the ACS-ECU connector +BV terminal and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 11.
 
STEP 6. Measure the resistance at the ASC-ECU connector.
(1) Connector check: the ASC-ECU connector and the junction block
(2) Disconnect the ASC-ECU connector.
(3) Measure the resistance between the IG1 terminal and body ground.
OK: No continuity
Is the check result normal?
Go to Step 7.
The power supply circuit may be short. Repair the wiring harness wires or connectors between the ACS-ECU connector IG1 terminal and the junction block. Then go to Step 11.
 
STEP 7. Measure the voltage at the ASC-ECU connector.
(1) Disconnect the ASC-ECU connector.
(2) Measure the voltage between +BV terminal and body ground.
OK: Battery voltage
Is the check result normal?
Go to Step 8.
The power supply circuit may be open. Repair the wiring harness wires or connectors between the ACS-ECU connector +BV terminal and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 11.
 
STEP 8. Measure the voltage at the ASC-ECU connector.
(1) Disconnect the ASC-ECU connector.
(2) Ignition switch: "ON"
(3) Measure the voltage between the IG1 terminal and body ground.
OK: Battery voltage
Is the check result normal?
Go to Step 9.
The power supply circuit may be open. Repair the wiring harness wires or connectors between the ACS-ECU connector IG1 terminal and the junction block. Then go to Step 11.
 
STEP 9. Measure the resistance at the ASC-ECU connector.
(1) Disconnect the ASC-ECU connector.
(2) Measure the resistance between the GND1 terminal and body ground as well as between the GND2 terminal and body ground.
OK: Continuity exists (2 Ω or less).
Is the check result normal?
Go to Step 10.
The ground circuit may be open. Repair the wiring harness wires or connectors between the ACS-ECU connector GND1 terminal and the fusible links as well as between the GND2 terminal and the fusible links. Then go to Step 11.
 
STEP 10. Check whether the diagnostic trouble code is set again.
Check again if the diagnostic trouble code is set.
(1) Erase the set diagnostic trouble code.
(2) Ignition switch: "LOCK" (OFF)
(3) Ignition switch: "ON"
Is diagnostic trouble code No. C1861 set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 11.
The trouble can be an intermittent malfunction (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
 
STEP 11. Check whether the diagnostic trouble code is set again.
Check again if the diagnostic trouble code is set.
(1) Erase the set diagnostic trouble code.
(2) Ignition switch: "LOCK" (OFF)
(3) Ignition switch: "ON"
Is diagnostic trouble code No. C1861 set?
Return to Step 3.
This diagnosis is complete.