Code No.P1779 (1st), P1780 (2nd), P1781 (3rd), P1782 (4th), P1784 (reverse): Gear incorrect ratio <4A/T>


OPERATION



DIAGNOSIS CODE SET CONDITIONS




PROBABLE CAUSES



  • Malfunction of input shaft speed sensor
  • Malfunction of output shaft speed sensor
  • Damaged harness wires and connectors
  • Malfunction of the A/T-ECU
  • Malfunction of solenoid valve
  • Malfunction of underdrive clutch retainer
  • Malfunction of valve body
  • Malfunction of transfer drive gear or driven gear
  • Malfunction of low-reverse brake system (for diagnosis codes P1779, P1784)
  • Malfunction of underdrive clutch system (for diagnosis codes P1779, P1780, P1781)
  • Malfunction of second brake system (for diagnosis codes P1780, P1782)
  • Malfunction of overdrive clutch system (for diagnosis codes P1781, P1782)
  • Malfunction of reverse clutch system (for diagnosis code P1784)
  • Malfunction of one-way clutch system (for diagnosis code P1779)

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code
If either of diagnosis codes P1779, P1780, P1781, P1782 and P1784 is stored, the input shaft speed sensor or output shaft speed sensor is defective.

Q. Is diagnosis code No. P1766 (P0715) or No. P1767 (P0720) stored?
YES <diagnosis code P1766 (P0715) is stored> : Refer to diagnosis code P1766 (P0715) input shaft speed sensor system .
YES <diagnosis code P1767 (P0720) is stored> : Refer to diagnosis code P1767 (P0720) output shaft speed sensor system .
Go to Step 2.

STEP 2. M.U.T.-III diagnosis code
If either of diagnosis codes P1779, P1780, P1781, P1782 and P1784 is stored, the corresponding solenoid valve is defective.

Q. Is either of diagnosis codes P1773 (P0750), P1774 (P0755), P1775 (P0760) and P1776 (P0765) stored?
YES <diagnosis code P1773 (P0750) is stored> : Refer to diagnosis code P1773 (P0750): Low-reverse solenoid valve system .
YES <diagnosis code P1774 (P0755) is stored> : Refer to diagnosis code P1774 (P0755): Underdrive solenoid valve system .
YES <diagnosis code P1775 (P0760) is stored> : Refer to diagnosis code P1775 (P0760): Second solenoid valve system .
YES <diagnosis code P1776 (P0765) is stored> : Refer to diagnosis code P1776 (P0765): Overdrive solenoid valve system .
Go to Step 3.

STEP 3. Hydraulic pressure test
Each hydraulic pressure of the elements below, which diagnosis codes indicate, should be within the standard value.

  • diagnosis code P1779: Underdrive clutch, low-reverse brake
  • diagnosis code P1780: Underdrive clutch, second brake
  • diagnosis code P1781: Underdrive clutch, overdrive clutch
  • diagnosis code P1782: Overdrive clutch, second brake
  • diagnosis code P1784: Reverse clutch, low-reverse brake
OK: Refer to Hydraulic Pressure Test .

Q. Is the check result normal?
Go to Step 6.
NO <some hydraulic pressures are abnormal> : Go to Step 5.
NO <all hydraulic pressure are abnormal> : Go to Step 4.

STEP 4. Adjust the line pressure and recheck the diagnosis code.
(1)Adjust the line pressure (Refer to ).
(2)Test drive the vehicle.
(3)Check the diagnosis code.

Q. Is the diagnosis code stored?
Go to Step 5.
The inspection is complete.

STEP 5. Disassemble, clean and assemble the valve body and recheck the diagnosis code.
(1)Check the mounting bolts for looseness, and the O-ring, solenoid valve and valve body for damage.
Replace the valve body assembly if the damages are thought to be irreparable.
(2)Test drive the vehicle.
(3)Check the diagnosis code.

Q. Is the diagnosis code stored?
Go to Step 7.
The inspection is complete.

STEP 6. 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 stored?
Go to Step 7.
The inspection is complete.

STEP 7. Check the A/T internal clutch and brake, and then recheck the diagnosis code.
(1)Check the following clutches or brakes according to the stored diagnosis codes, replace if necessary.

  • If diagnosis code P1779, P1780, P1781 are stored individually or in a group, replace the underdrive clutch.
  • If diagnosis code P1781, P1782 are stored individually or in a group, replace the overdrive clutch.
  • If diagnosis code P1784 is stored, replace the reverse clutch.
  • If diagnosis code P1779, P1784 are stored individually or in a group, replace the low-reverse brake.
  • If diagnosis code P1780, P1782 are stored individually or in a group, replace the second brake.
  • If diagnosis code P1779 is stored, replace the one-way clutch.
(2)Test drive the vehicle.
(3)Check the diagnosis code.

Q. Is the diagnosis code stored?
Eliminate the cause of the noise.
The inspection is complete.