P0731 - GEAR 1 INCORRECT RATIO

The error code P0731 OBD2 is set on vehicles equipped with automatic transmission. The reason for its setting has to do with failure when driving in 1st gear or when shifting to 6th gear.

To increase vehicle speed and maximum engine power output, vehicle computer-controlled transmission uses various transmission ratios.

The Engine Control Module (ECM) uses the information provided by transmission input and output sensors to compare speeds, and it verifies that the precise transmission ratio is present in the 1st gear. If the ECM determines that the transmission ratio is outside of the specified value, this DTC code is set.

• MIL light.
• Lack of power.
• Transmission slippage.
• Erratic transmission changes.

The factors that lead to the establishment of fault code P0731 OBDII are

• The transmission fluid may be contaminated or the level may be low.
• The transmission could be malfunctioning.
• The main control of the transmission may be blocked internally.
• Bad switch solenoid.
• Transmission Control Module (TCM) in bad condition.

To solve the failures of DTC code P0731 OBDII, do the following:

• Check the level of the transmission fluid and its condition.
• Verify that the shift control solenoid circuit is working properly.
• Check the oil pressure. Then, consult the service manual for oil pressure specifications for each gear unit. If the result is that it is outside the specifications, it indicates that there is a loss of pressure somewhere, locate it, and make the appropriate repair.
• Disconnect the transmission rate sensors, then use a multimeter to check the resistance values. Compare with the specifications in the service manual, if they do not match, you must change the sensors.
• Check the circuit wires. Make sure they have continuity, no defects. Repair or replace them as necessary.
• Examine the TCM. Measure the electrical values to check its proper functioning.