Code No. P0731: 1st Gear Incorrect Ratio


DIAGNOSIS CODE SET CONDITIONS


*1*2
note *1 The actual gear ratio deviates from the target gear ratio to the low engine (turbine) speed.
note *2 The actual gear ratio deviates from the target gear ratio to the high engine (turbine) speed.

PROBABLE CAUSES



  • Transmission assembly powertrain parts failure
  • Malfunction of the P0715: input shaft speed sensor system
  • Malfunction of the P0720: output shaft speed sensor system
  • Malfunction of the P0748: line pressure linear solenoid valve system circuit
  • Malfunction of the P0753: low clutch linear solenoid valve system circuit
  • Malfunction of the P1758: low-reverse brake shift solenoid valve system circuit
  • Malfunction of the low clutch
  • Malfunction of the low one-way clutch
  • Malfunction of the valve body assembly

DIAGNOSIS PROCEDURE

STEP 1. Check the diagnosis code.
Check that P0715 (input shaft speed sensor) and P0720 (output shaft speed sensor) are set.

Q. Is the diagnosis code set?
Check and repair the relevant diagnosis code system.
Go to Step 2.

STEP 2. Check the diagnosis code.
Check if the diagnosis code other than P0731 (1st gear ratio) is set.

Q. Is the diagnosis code set?
Check and repair the relevant diagnosis code system.
Go to Step 3.

STEP 3. Check the A/T fluid properties.
Check the status of the A/T fluid properties (smell, colour, fouling).

  • Black: A/T inside damage, seizure
  • Milky: Water intrusion

Q. Is the check result normal?
Go to Step 4.
Remove the A/T from the vehicle, then check and repair the inside.

STEP 4. Check the A/T fluid level.

Q. Is the check result normal?
Go to Step 5.
Adjust the A/T fluid level, and then go to Step 5.

STEP 5. Check the signals of input shaft speed sensor and output shaft speed sensor.
Check the signals of A/T-ECU connector PGA1, PGB1 terminal.
Refer to .

Q. Is the check result normal?
Go to Step 6.
Repair or replace the failure section.

STEP 6. Hydraulic pressure test
Refer to .

Q. Is the check result normal?
Go to Step 7.
Remove the A/T from the vehicle, then check and repair the inside.

STEP 7. Erase the diagnosis code, and drive the vehicle for a while.
Check that the normal code is displayed.

Q. Is the check result normal?
The procedure is complete.
Return to Step 1.