Code No.P1788 (P1751) A/T control relay system

OPERATION

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 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 <4M4>
Malfunction of the engine-A/T-ECU <6G7>

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

Item 8: 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

Refer to

Q. Is the check result normal?

	Go to Step 3.

	Replace the A/T control relay.

STEP 3. Connector check: D-110 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 D-110.

Disconnect the A/T control relay, and measure the voltage between terminal No.1 and earth at the relay box side.

OK: System voltage

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 5.

STEP 5. Connector check: A-03 <LHD> or D-137 <RHD> intermediate connector, D-113 J/C (6) <4M4>

Check for the contact with terminals.

Q. Is the check result normal?

	Go to Step 6.

	Repair the defective connector.

STEP 6. Check the harness between A/T control relay connector D-110 terminal No.1 and battery.

Check the power supply line for short or open circuit.

Q. Is the check result normal?

	Go to Step 7.

	Repair the wiring harness.

STEP 7. M.U.T.-III data list

Item 8: Relay voltage (Refer to data list reference table

Q. Is the check result normal?

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

	Replace the A/T-ECU <4M4> or engine-A/T-ECU <6G7>.

STEP 8. Measure the voltage at the A/T control relay connector D-110.

(1)Turn the ignition switch to the ON position.

(2)Disconnect the A/T control relay, and measure the voltage between terminal No.4 and earth at the relay box side.
OK: System voltage

Q. Is the check result normal?

	Go to Step 11.

	Go to Step 9.

STEP 9. Connectors check: A-03 <LHD>or D-137 <RHD> intermediate connector, D-401 J/B connector

Check for the contact with terminals.

Q. Is the check result normal?

	Go to Step 10.

	Repair the defective connector.

STEP 10. Check the wiring harness between A/T control relay connector D-110 terminal No.4 and J/B connector D-401 terminal No.12.

Check the power supply line for short or open circuit.

Q. Is the check result normal?

	Go to Step 7.

	Repair the wiring harness.

STEP 11. Measure the voltage at A/T-ECU connector D-139 <4M4> or engine-A/T-ECU connector D-218 <6G7>.

(1)Install the A/T control relay.

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

(3)Measure the voltage between A/T-ECU connector D-139 terminal No.2, No.3 <4M4> and earth or engine-A/T-ECU connector D-218 terminal No.123, No.124 <6G7> and earth.
OK: System voltage

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 12.

STEP 12. Connector check: D-139 A/T-ECU connector <4M4> or D-218 engine-A/T-ECU connector <6G7>, D-113 J/C (6) <4M4>

Check for the contact with terminals.

Q. Is the check result normal?

	Go to Step 13.

	Repair the defective connector.

STEP 13. Check the harness between A/T control relay connector D-110 terminal No.3 and A/T-ECU connector D-139 terminal No.2, 3 <4M4> or engine-A/T-ECU connector D-218 terminal No.123, 124 <6G7>.

Check the power supply line for short or open circuit.

Q. Is the check result normal?

	Go to Step 7.

	Repair the wiring harness.

STEP 14. Connector check: D-139 A/T-ECU connector <4M4> or D-218 engine-A/T-ECU connector <6G7>

Check for the contact with terminals.

Q. Is the check result normal?

	Go to Step 15.

	Repair the defective connector.

STEP 15. Check the harness between A/T control relay connector D-110 terminal No.2 and A/T-ECU connector D-139 terminal No.71 <4M4> or engine-A/T-ECU connector D-218 terminal No.127 <6G7>.

Check the output line for short or open circuit.

Q. Is the check result normal?

	Go to Step 7.

	Repair the wiring harness.