Error Code P0780 is defined as Transmission Shift Malfunction. This means a problem in the automatic transmission shifting has been detected. An error usually caused by mechanical failure or electronic malfunction. Note that this code is exclusive to vehicles with automatic transmission.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, particularly vehicles made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course vary from one vehicle manufacturer and/or model to another.

Definition

The job of the automatic transmission is to match the optimum power and torque of the engine, based on the characteristics of the driver, i.e. rate of acceleration and speed, through auto-selecting different gear ratios or speed to power the wheels.

When Error Code P0780 is set, that means the PCM (powertrain control module, or also known as ECM or engine control module) is seeing an RPM that is smaller or greater than the manufacturer’s specified RPM difference between the rotational speed of Transmission Output Shaft and the Input Shaft as the transmission shift gears. This issue can happen during shifting, or when driving at steady speed in the same gear, and often means the transmission is slipping or not shifting properly.

Common Symptoms

As with other error codes P0780 activates the Check Engine light as one of its most obvious symptoms. Other symptoms include:

  • Erratic transmission shift problems
  • Transmission slippage
  • Delayed transmission engagement
  • Whining noise coming from transmission pump
  • Harsh transmission shifts (particularly if the controller is in limp-in mode)
  • Increase in fuel consumption

In some unusual cases, the vehicle may not show adverse conditions, while in other cases the vehicle may show performance problems such as dying when coming to a stop at freeway and/or misfire-like symptoms.

Possible Causes

There are many factors that lead to the development of Error Code P0780, which include:

  • Burnt, dirty, or outdated transmission fluid
  • Low transmission fluid
  • Bad electronic pressure regulator
  • Shorted or open transmission control harness circuits
  • Defective shift solenoid(s)
  • Failed transmission pump
  • Mechanical failure (torque converter failure, wear and tear of internal components, or clutch failure)
  • Defective or programming error in the PCM

How to Check

As with other error codes, diagnosing P0780 requires recording of freeze frame data, and then replicating the conditions when the code was set in a test drive; this includes the engine load, road speed, RPM, and throttle position.

To start the diagnosis, technicians make a visual inspection of the transmission and all the related wiring harness. They pay close attention to the wirings routed near sharp edges or hot exhaust components.

Technicians will also monitor the RPM input speed and compare that to the output speed of the RPM on a smooth flat surface after the vehicle warms up and the fuel system is in closed loop.

From there, technicians start from a dead spot and gently accelerate up to the mph range when the freeze frame was recorded. They take note of the serial shift solenoid PIDs and determine if they are right, that is when the transmission shift smoothly from 1st to 2nd gear, or if there is a “flare up” in the RPM between shifts. If there is a flare up, then the problem may be indicative of a slipping transmission and may verify the Error Code P0780.

How to Fix

  • Repair or replace damages in wiring and connectors in the transmission or other related wiring harness
  • Repair or replace shorted or open transmission control harness circuits
  • Replace or refill for a new transmission fluid
  • Repair or replace transmission control wiring and shift solenoids
  • Replace transmission pump

Some of the most common misdiagnosis of this error code is engine misfire problem, driveline problem, and internal transmission problem. This is because symptoms can be similar to such conditions. Thus, it is important to have a thorough diagnosis by a certified technician.

Error Code P07800 must be addressed as soon as possible, as even minor condition could develop into a more catastrophic problem if left unattended for an extended period of time.