Code No.P1790 Back up line system

OPERATION


Always power is supplied to the ECU to prevent the reset of A/T-ECU memory when the ignition switch is turned to the LOCK (OFF) position.

DIAGNOSIS CODE SET CONDITION


If the battery voltage is 10 V or more and back-up voltage is less than 6 V while the ignition switch is ON position for 2 seconds or more, it is judged that there is a open circuit in the back-up line and diagnosis code No. P1790 is set.

PROBABLE CAUSES



DIAGNOSIS PROCEDURE

STEP 1. Measure the voltage at A/T-ECU connector C-12.

(1)Measure the voltage between A/T-ECU connector C-12 terminal No.38 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4.

Go to Step 2.

STEP 2. Connectors check: A-115 intermediate connector, C-12 A/T-ECU connector.


Check for the contact with terminals.

Q. Is the check result normal?

Go to Step 3.

Repair the defective connector.

STEP 3. Check the harness between A/T-ECU connector C-12 terminal No.38 and fusible link.

Check the power supply line for short or open circuit.

Q. Is the check result normal?

Go to Step 5.

Repair the wiring harness.

STEP 4. Connector check: C-12 A/T-ECU connector.

Check for the contact with terminals.

Q. Is the check result normal?

Go to Step 5.

Repair the defective connector.

STEP 5. Replace the A/T-ECU and then recheck the diagnosis code.
(1)Replace the A/T-ECU.
(2)Test drive the vehicle.
(3)Check the diagnosis code.

Q. Is the diagnosis code set?
Go to Step 1.
The inspection is complete.