P0780 OBD-II: Shift Error

What Does P0780 Code Mean?

OBD-II Code P0780 is defined as a Transmission Shift 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.

When the code P0780 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is seeing a greater or smaller than specified RPM difference between the rotational speed of the Input Shaft and the Transmission Output Shaft as the transmission shifts gears. This can occur during shifting or when driving at steady speeds in the same gear. It often implies that the transmission is slipping or shifting improperly.

P0780 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 P0780 Code

• Defective Shift Solenoids
• Defective Engine Coolant Temperature Sensor
• Defective Torque Converter Lockup solenoid
• Defective Torque Converter Clutch
• Defective Transmission Range Sesnor
• 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

P0780 Diagnostic Theory for Shops and Technicians

When diagnosing a P0780 code, it is important to record any other codes and the P0780 freeze frame data. Then one should duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed because a P0780 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. Start from a dead stop and gently accelerate up to the mph range that was recorded in the freeze frame. Watch the serial shift solenoid PIDs and determine if they seems rational, that is, does the transmission shift smoothly from 1st gear to 2nd gear, or is there an rpm 'flare up' between shifts. If there is, then this could indicate that the transmission is slipping and may verify the P0780 code.