P0734 - OBD II Trouble Code

Auto Systems and Repair

Gear 4 Incorrect Ratio 

Our emissions expert has put together the following information about the P0734 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

  • OBD II P0734

Fault Code Definition

  • Gear 4 Incorrect Ratio
What does this Mean?
The purpose of the automatic transmission is to match the engine's optimum power and torque characteristics to the driver's desired rate of acceleration and speed by auto-selecting different gear ratios or 'speeds' to power the wheels. 
Code P0734  When the code P0734 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is seeing a greater than a specified RPM difference between the rotational speed of the Input RPM Sensor and the Transmission Output RPM Sensor when the vehicle is in 4th gear.  This can occur during shifting or when driving at steady speeds. It often implies that the transmission is slipping.  

Symptoms

  • Check Engine Light will illuminate
  • Vehicle will not shift properly
  • Decrease in fuel economy
  • In unusual cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as dying when coming to a stop after driving on the freeway and/or misfire-like symptoms

Common Problems That Trigger the P0733 Code

  • Defective 4th gear related shift solenoid
  • Defective 4th gear related gear set or clutch pack 
  • Defective Engine Coolant Temperature Sensor
  • Defective Valve Body
  • Dirty transmission fluid that restricts the hydraulic passages

Common Misdiagnoses

  • Engine Misfire problem
  • Internal Transmission problem
  • Driveline problem

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
P0734 Diagnostic Theory for Shops and Technicians
When diagnosing a P0734 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed because a P0734 can be difficult to detect.

One should monitor the RPM input speed and compare that to output speed RPM on a smooth, flat surface after the vehicle is warmed up and the fuel system is in a closed loop. Monitor how the 4th gear solenoid configuration responds to an increased amount of throttle. The 4th  gear related solenoids should stay in the 4th gear configuration and the transmission should NOT slip. 

 

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