P0730 OBD-II: Incorrect Gear Ratio

What Does P0730 Code Mean?

OBD-II Code P0730 is defined as a Transmission Control System Malfunction

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 P0730 means that the Powertrain Computer or PCM is seeing greater than a specified RPM difference between the rotational speed of the Input RPM Sensor and the Transmission Output RPM Sensor. This can occur during shifting or when driving at steady speeds in the same gear. It often implies that the transmission is slipping.

P0730 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 P0730 Code

• Defective Shift Solenoids
• 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

P0730 Diagnostic Theory for Shops and Technicians

When diagnosing a P0730 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 and compare the Output RPM Speed Sensor signal to the Input RPM Speed Sensor signal. If the input RPM signal varies a lot when your're traveling at a steady road speed and throttle position, then you may have verified the P0730 code setting condition.

I also like to drive the vehicle at a steady freeway speed, say 60 mph, so the transmission can shift into its highest gear. Then I watch the Input and Output RPM Speed Sensor signal. If there is more than a 200 RPM difference at a steady speed and throttle position, I know the transmission is slipping and may need internal repairs.