[Previous][Next]
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 stored. 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.
 
 
 
 
OPERATION
  • Power is supplied to the EPS-ECU from the battery or the ignition switch.
 
 
DIAGNOSTIC TROUBLE CODE SET CONDITION
The power supply voltage is less than a predetermined voltage stored in the microcomputer, and the microcomputer determines that there is a problem in the power supply system.
 
 
PROBABLE CAUSES
  • Malfunction of CAN bus line
  • Defective battery
  • Charging system failed
  • Defective harness wire(s) or connector(s)
    • Short or open circuit between the EPS-ECU, the ETACS-ECU and the fusible link or loose connector contact
    • Open circuit between the body ground and the EPS-ECU or loose connector contact
  • Malfunction of the EPS-ECU
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.
Use scan tool MB991958 to diagnose the CAN bus lines.
Is the check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ). On completion, go to Step 2.
 
STEP 2. Diagnostic trouble code recheck after resetting CAN bus lines
(1) Erase the diagnostic trouble code.
(2) Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3) Check if the diagnostic trouble code is stored.
Is diagnostic trouble code C1861 stored?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Check the battery voltage.
Start the engine and measure the battery voltage (Refer to GROUP 54A - Battery ).
Is the check result normal?
Go to Step 4.
Check the battery and repair if necessary (Refer to GROUP 54A - Battery , ). Then go to Step 10.
 
STEP 4. Check the charging system.
Start the engine and measure the charging system (Refer to GROUP 16 - On-vehicle Service/Generator Output Line Voltage Drop Test )
Is the check result normal?
Go to Step 5.
Check the charging system and repair if necessary (Refer to GROUP 16 - Generator Assembly ). Then go to Step 10.
 
STEP 5. Wiring harness check
(1) Check the wiring harness between the EPS-ECU connector terminal +BB and the fusible link for damage or other problem.
(2) Check the wiring harness between the junction block connector terminal and the fusible link for damage or other problem.
(3) Check the wiring harness between the EPS-ECU connector terminal GND and the body ground point for damage or other problem.
Is the check result normal?
Go to Step 6.
Repair the defective connector(s) or terminal(s), or repair the defective wiring harness. Then go to Step 10.
 
STEP 6. Voltage measurement at the junction block connector
(1) Measure the junction block voltage without disconnecting the connector (by backprobing).
(2) Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3) Measure the voltage between the junction block connector terminals.
OK: Battery voltage
Is the check result normal?
Go to Step 7.
Check the fusible link or the junction block and repair if necessary. Then go to Step 10.
 
STEP 7. Voltage measurement at the EPS-ECU connector
(1) Measure the EPS-ECU voltage without disconnecting the connector (by backprobing).
(2) Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3) Measure the voltage between the EPS-ECU connector terminal IG1 and the EPS-ECU connector terminal GND.
OK: Battery voltage
(4) Measure the voltage between the EPS-ECU connector terminals +BB and GND.
OK: Battery voltage
Is the check result normal?
Go to Step 8.
Check the fusible link or the junction block and repair if necessary. Then go to Step 10.
 
STEP 8. Using scan tool MB991958, check data list.
Check the following data list (Refer to ).
  • Item No. 22: Power relay voltage
  • Item No. 23: Ignition voltage
Is the check result normal?
Go to Step 10.
Go to Step 9.
 
STEP 9. Check whether the diagnostic trouble code is stored again.
(1) Erase the diagnostic trouble code.
(2) Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3) Check if the diagnostic trouble code is stored.
Is diagnostic trouble code C1861 stored?
Replace the EPS-ECU (Refer to ). Then go to Step 10.
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunctions ).
 
STEP 10. Check whether the diagnostic trouble code is stored again.
(1) Erase the diagnostic trouble code.
(2) Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3) Check if the diagnostic trouble code is stored.
Is diagnostic trouble code C1861 stored?
Return to Step 1.
This diagnosis is complete.