Code No.C1861: Low voltage at ABS-ECU power supply

caution

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 ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

The ABS-ECU is energised by the ignition switch (IG1) through J/B fuse.
Power supply for ABS solenoid valve is supplied to the ABS-ECU via fusible link.
Power supply for ABS motor is supplied to the ABS-ECU via fusible link.
The wheel speed sensors are energised via ABS-ECU.

DIAGNOSIS CODE SET CONDITIONS

The ABS-ECU monitors the ABS-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

Battery failure
Charging system failed
Damaged harness wires and connectors
Malfunction of the hydraulic unit assembly (integrated with ABS-ECU)

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnosis

Use the M.U.T.-III to diagnose the CAN bus lines.

Q. 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. Diagnosis code recheck after resetting CAN bus lines

(1)Turn the ignition switch to the "LOCK" (OFF) position.

(2)Turn the ignition switch to the "ON" position.

(3)Erase the diagnosis code.

(4)Turn the ignition switch to the "LOCK" (OFF) position.

(5)Turn the ignition switch to the "ON" position.

(6)Check if the diagnosis code is set.

Q. Is diagnosis code No. C1861 set?

	Go to Step 3.

	This diagnosis is complete.

STEP 3. Check the battery.

Refer to GROUP 54A - Battery Test

Q. Is the check result normal?

	Go to Step 4.

	Charge or replace the battery (Refer to GROUP 54A - Battery ). Then go to Step 13.

STEP 4. Check the charging system.

Refer to GROUP 16 - Charging System

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the charging system component(s) (Refer to GROUP 16 - Alternator ). Then go to Step 13.

STEP 5. Measure the resistance at the ABS-ECU connector.

(1)Connector check: the ABS-ECU connector, the fuses (relay box) and the fusible links

(2)Check the ABS-ECU connector.

(3)Disconnect the connector and measure at the wiring harness side.

(4)Measure the resistance between +BV terminal and body earth.
OK: No continuity

Q. 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 ABS-ECU connector +BV terminal and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 13.

STEP 6. Measure the resistance at the ABS-ECU connector.

(1)Connector check: the ABS-ECU connector and the fusible links

(2)Check the ABS-ECU connector.

(3)Disconnect the connector and measure at the wiring harness side.

(4)Measure the resistance between +BM terminal and body earth.
OK: No continuity

Q. 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 ABS-ECU connector +BM terminal and the fusible links. Then go to Step 13 .

STEP 7. Measure the resistance at the ABS-ECU connector.

(1)Check the connectors and the junction block.

(2)Disconnect the ABS-ECU connector.

(3)Measure the resistance between the IG1 terminal and body earth.
OK: No continuity

Q. Is the check result normal?

	Go to Step 8.

	The power supply circuit may be short. Repair the wiring harness wires or connectors between the ABS-ECU connector IG1 terminal and the junction block. Then go to Step 13.

STEP 8. Measure the voltage at the ABS-ECU connector.

(1)Disconnect the ABS-ECU connector.

(2)Measure the voltage between +BV terminal and body earth.
OK: Battery voltage

Q. 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 ABS-ECU connector +BV terminal and the fusible links, the fuse (relay box) or the fusible links. Then go to Step 13.

STEP 9. Measure the voltage at the ABS-ECU connector.

(1)Disconnect the ABS-ECU connector.

(2)Measure the voltage between +BM terminal and body earth.
OK: Battery voltage

Q. Is the check result normal?

	Go to Step 10.

	The power supply circuit may be open. Repair the wiring harness wires or connectors between the ABS-ECU connector +BM terminal and the fusible links. Then go to Step 13 .

STEP 10. Measure the voltage at the ABS-ECU connector.

(1)Disconnect the ABS-ECU connector.

(2)Turn the ignition switch to the "ON" position.

(3)Measure the voltage between the IG1 terminal and body earth.
OK: Battery voltage

Q. Is the check result normal?

	Go to Step 11.

	The power supply circuit may be open. Repair the wiring harness wires or connectors between the ABS-ECU connector IG1 terminal and the junction block. Then go to Step 13.

STEP 11. Measure the resistance at the ABS-ECU connector.

(1)Disconnect the ABS-ECU connector.

(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).

Q. Is the check result normal?

	Go to Step 12.

	The earth circuit may be open. Repair the wiring harness wires or connectors between the ABS-ECU connector GND1 terminal and the fusible links as well as between the GND2 terminal and the fusible links. Then go to Step 13.

STEP 12. Check whether the diagnosis code is set again.

(1)Turn the ignition switch to the "LOCK" (OFF) position.

(2)Turn the ignition switch to the "ON" position.

(3)Erase the diagnosis code.

(4)Turn the ignition switch to the "LOCK" (OFF) position.

(5)Turn the ignition switch to the "ON" position.

(6)Check if the diagnosis code is set.

Q. Is diagnosis code No. C1861 set?

	Replace the hydraulic unit assembly (integrated with ABS-ECU) (Refer to ). Then go to Step 13.

	The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 13. Check whether the diagnosis code is set again.

(1)Turn the ignition switch to the "LOCK" (OFF) position.

(2)Turn the ignition switch to the "ON" position.

(3)Erase the diagnosis code.

(4)Turn the ignition switch to the "LOCK" (OFF) position.

(5)Turn the ignition switch to the "ON" position.

(6)Check if the diagnosis code is set.

Q. Is diagnosis code No. C1861 set?

	Return to Step 1.

	The procedure is complete.