Code No. C1861: Abnormal power supply voltage (too low)







caution
  • If the EPS-ECU sets the diagnosis code No. C1861, diagnose the CAN bus lines. If there is any fault in the CAN bus lines, an incorrect diagnosis code may be set.
  • Before replacing ECU, ensure that the communication circuit is normal.

DIAGNOSIS CODE SET CONDITIONS



  • 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.
    • Criteria for judging malfunction
    • The relay contact voltage is less than 9 V.

PROBABLE CAUSES



  • Malfunction of the auxiliary battery
  • Malfunction of the on board charger/on board transformer
  • Malfunction of the EPS-ECU
  • Damaged wiring harness or connector

DIAGNOSIS PROCEDURE

STEP 1. Check the auxiliary battery voltage..
Start the electric motor unit, and measure the auxiliary battery voltage.

Q. Is the voltage 10 V or more?
Go to Step 2.
Check the auxiliary battery and on board charger/on board transformer, and repair if necessary. (Refer to GROUP 54A - Auxiliary Battery - Battery Test as well as GROUP 54D - On Board Charger/On Board Transformer Removal and Installation .)

STEP 2. Voltage measurement at B-114 EPS-ECU connector
(1)Disconnect the connector and measure at the wiring harness side.
(2)Measure the voltage between B-114 EPS-ECU connector terminal No. 2 and the body earth.
OK: Battery voltage

Q. Is the check result normal?
Go to Step 3.
Check the wiring harness and connector between the fusible link No. 23 and the EPS-ECU, and repair if necessary.

STEP 3. Measure the resistance at B-114 EPS-ECU connector.
(1)Disconnect the connector and measure at the wiring harness side.
(2)Measure the resistance between B-114 EPS-ECU connector terminal No. 1 and the body earth.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?
Go to Step 4.
Check the wiring harness and connector between the body earth and the EPS-ECU, and repair if necessary.

STEP 4. Diagnosis code recheck
Recheck if the diagnosis code is set.
(1)Turn the electric motor switch to the "LOCK" (OFF) → "ON" position.
(2)Check if the diagnosis code No. C1861 is set as a current trouble.

Q. Is diagnosis code C1861 set?
Replace EPS-ECU.
Intermittent malfunction. (Refer to GROUP 00 - How to Cope with Intermittent Malfunction .)