If a fail-safe operation is activated, the A/T control relay shuts off the power
supply to the solenoid valve in accordance with the signal from the A/T-ECU.
DIAGNOSIS CODE SET CONDITION
Code No.P1788 (P1751) will be set if the A/T control voltage is less than 7 V
after the ignition switch is turned on. If code No.P1788 (P1751) is set, the transmission will be held in 3rd gear.
PROBABLE CAUSES
Malfunction of A/T control relay
Damaged harness wires and connectors
Malfunction of the A/T-ECU
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III data list
Item 08: Relay voltage (Refer to data list reference table .)
Q.
Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 -
How to Cope with Intermittent
Malfunction .)
Go to Step 2.
STEP 2. Check the A/T control relay connector
Refer to .
Q.
Is the check result normal?
Go to Step 3.
Replace the A/T control relay.
STEP 3. Connector check: A-19X A/T control relay connector
Check for the contact with terminals.
Q.
Is the check result normal?
Go to Step 4.
Repair the defective connector.
STEP 4. Measure the voltage at A/T control relay connector
A-19X.
Disconnect the A/T control relay, and measure the voltage between terminal No.4
and earth at the relay box side. OK: System voltage