P1788

DTC P1788 (P1751): A/T Control Relay System






























CIRCUIT OPERATION

- A/T control relay (terminal 1) receives the battery positive voltage through a dedicated 20 amp fuse.
- When the ignition switch is turned to the "ON" position, the PCM (terminal 82) receives battery voltage from the ignition switch. The PCM (terminal 82) applies voltage to energize the A/T control relay (terminal 3). With the A/T control relay energized, system voltage is applied to the PCM (terminals 70 and 57).

DESCRIPTIONS OF MONITOR METHODS

- If relay output voltage is below specified value, PCM judges that A/T control relay has a failure.

MONITOR EXECUTION

- Continuous

MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)

- DTC P1779 (P0731): 1st gear incorrect ratio
- DTC P1780 (P0732): 2nd gear incorrect ratio
- DTC P1781 (P0733): 3rd gear incorrect ratio
- DTC P1782 (P0734): 4th gear incorrect ratio
- DTC P1783 (P0735): 5th gear incorrect ratio[ 5A/T]
- DTC P1784 (P0736): Reverse gear incorrect ratio
- DTC P1778 (P0743): Torque converter clutch solenoid malfunction
- DTC P1773 (P0753): Low-reverse solenoid malfunction
- DTC P1774 (P0758): Underdrive solenoid malfunction
- DTC P1775 (P0763): Second solenoid malfunction
- DTC P1776 (P0768): Overdrive solenoid malfunction
- DTC P1777 (P0773): Reduction solenoid malfunction[ 5A/T]
Sensor (The sensor below is determined to be normal)

- Torque converter clutch solenoid
- Low-reverse solenoid
- Underdrive solenoid
- Second solenoid
- Overdrive solenoid
- Reduction solenoid[ 5A/T]

LOGIC FLOW CHARTS (Monitor Sequence)





DTC SET CONDITIONS

Check Conditions

- Voltage of battery: 9 volts or more.
- Time after PCM turns on A/T control relay: 0.5 second or more.
Judgement Criteria

- A/T control relay output voltage: 7 volts or less. (0.1 second)
- If DTC P1788 (P1751) is set consecutively four times, the transaxle is locked into 3rd gear as a fail-safe measure, and the selector lever position indicator light (D, 1 through 4 or 5) flashes once per second.

OBD-II DRIVE CYCLE PATTERN

Start the engine, and keep the vehicle stopped in "P" range for 5 seconds.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)

- Malfunction of the A/T control relay
- Damaged harness or connector
- Malfunction of the PCM

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

STEP 1. Using scan tool MB991958, check data list item 8: A/T Control Relay Output Voltage.





(1)
CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.

Connect scan tool MB991958 to the data link connector.
(2)Turn the ignition switch to the "ON" position.
(3)Set scan tool MB991958 to the data reading mode.

- Item 8: A/T Control Relay Output Voltage.
- The voltage should equal battery positive voltage.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Does the measured voltage equal battery positive voltage?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.

NO Go to Step 2.

STEP 2. Check the A/T control relay.





(1)Remove the A/T control relay from the engine component relay box connector B-15X.





(2)Using jumper wires, connect terminal 2 to the positive battery terminal, and terminal 3 to the negative battery terminal.
(3)Measure the resistance between terminals 1 and 4 of the A/T control relay.

- The resistance should be measured less than 2 ohms.
- Disconnect the jumper wires. The resistance between terminals 1 and 4 should measure over limits (open circuit).

Q. Is the measured resistance less than 2 ohms when the relay is energized, and open circuit when the relay is de-energized?

YES Go to Step 3.

NO Replace the A/T control relay.

STEP 3. Check A/T control relay socket B-15X in the engine compartment relay box for loose, corroded or damaged terminals, or terminals pushed back in the socket.





Q. Is the relay connector in good condition?

YES Go to Step 4.

NO Repair or replace the damaged components. Harness Connector Inspection.

STEP 4. Measure the supply voltage at A/T control relay connector B-15X in the engine component relay box.





(1)Disconnect the A/T control relay.





(2)Measure the voltage between terminal 1 and ground.

- The measured voltage should equal battery positive voltage.

Q. Is the measured voltage equal to battery positive voltage?

YES Go to Step 7.

NO Go to Step 5.

STEP 5. Check intermediate connector A-15 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Are the connector and terminals in good condition?

YES Go to Step 6.

NO Repair or replace the damaged components. Harness Connector Inspection.

STEP 6. Check the harness for open circuit or short circuit to ground between A/T control relay connector B-15X terminal 1 in the engine component relay box and battery.





Q. Is the harness wire in good condition?

YES Go to Step 15.

NO Repair or replace the harness wire.

STEP 7. Measure the supply voltage at A/T control relay connector B-15X in the engine component relay box.





(1)Disconnect the A/T control relay.
(2)Turn the ignition switch to the "ON" position.





(3)Measure the voltage between terminal 2 and ground.

- The measured voltage should equal battery positive voltage.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the measured voltage equal to battery positive voltage?

YES Go to Step 10.

NO Go to Step 8.

STEP 8. Check intermediate connector A-15, C-24, joint connector (1) C-28 and junction block connector C-203 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

















Q. Are the connectors in good condition?

YES Go to Step 9.

NO Repair or replace the damaged components. Harness Connector Inspection.

STEP 9. Check the harness for open circuit or short circuit to ground between A/T control relay connector B-15X terminal 2 in the engine component relay box and junction block connector C-203 terminal 12.









Q. Is the harness wire in good condition?

YES Go to Step 15.

NO Repair or replace the harness wire.

STEP 10. Measure the A/T control relay output voltage at PCM connector B-20 by using check harness special tool MB991923.





(1)Disconnect all the connectors from the PCM.





(2)Connect special tool MB991923 (check harness) between the PCM and the body-side harness connector.
(3)Turn the ignition switch to the "ON" position.





(4)Measure the voltage between terminal 57 and ground.

- The measured voltage should equal battery positive voltage.





(5)Measure the voltage between terminal 70 and ground.

- The measured voltage should equal battery positive voltage.
(6)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the measured voltage equal to battery positive voltage between terminal 57 and ground, and between terminal 70 and ground?

YES Go to Step 13.

NO Go to Step 11.

STEP 11. Check PCM connector B-20 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Are the connector and terminals in good condition?

YES Go to Step 12.

NO Repair or replace the damaged components. Harness Connector Inspection.

STEP 12. Check harness for open circuit or short circuit to ground between A/T control relay connector B-15X (terminal 4) in the engine component relay box and PCM connector B-20 (terminals 57 and 70).









Q. Is the harness wire in good condition?

YES Go to Step 15.

NO Repair or replace the harness wire.

STEP 13. Check PCM connector B-20 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Are the connector and terminals in good condition?

YES Go to Step 14.

NO Repair or replace the damaged components. Harness Connector Inspection.

STEP 14. Check harness for open circuit or short circuit to ground between A/T control relay connector B-15X terminal 3 in the engine component relay box and PCM connector B-20 terminal 82.









Q. Is the harness wire in good condition?

YES Go to Step 15.

NO Repair or replace the harness wire.

STEP 15. Using scan tool MB991958, check data list item 8: A/T control relay output voltage.





(1)
CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.

Connect scan tool MB991958 to the data link connector.
(2)Turn the ignition switch to the "ON" position.
(3)Set scan tool MB991958 to the data reading mode.

- Item 8: A/T Control Relay Output Voltage.
- The voltage should equal battery positive voltage.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the measured voltage equal battery positive voltage?

YES It can be that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.

NO Replace the PCM. When the PCM is replaced, register the encrypted code. Encrypted Code Registration Criteria Table.