P0780 Shift Malfunction
OBD-II Trouble Code Technical Description
Shift Malfunction
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles (Ford, Honda, Mazda, Mercedes, VW, etc.). Although generic, the specific repair steps may vary depending on make/model.
What does that mean?
In my own personal experience, when a code P0780 is stored, it means that the powertrain control module (PCM) has detected a problem with automatic transmission shifting. This code may be caused by either a mechanical or an electronic malfunction but is limited to vehicles with automatic transmissions.
Automatic transmissions in OBD-II equipped vehicles are controlled by the PCM or a stand-alone transmission control module (TCM). Input signals from an array of engine and transmission sensors are used by the transmission controller to calculate transmission shift strategy. Electronic solenoid valves are then activated by the controller, allowing high pressure fluid to flow into the appropriate hydraulic circuit (in the valve body) and permit the transmission to up or down shift as required.
A powerful pump (integrated into the transmission housing and driven by the engine) is used to create the hydraulic pressure needed to accomplish smooth and efficient shifting functions. Since varying degrees of hydraulic pressure are required at different RPM levels and engine loads, the transmission controller regulates pressure via an electronic pressure regulator. The transmission pressure sensor and the transmission temperature sensor help the controller to monitor hydraulic pressure and make the necessary adjustments.
The transmission controller is programmed to compare input signals from the input speed sensor and output speed sensor to determine whether the transmission is shifting efficiently. If the PCM detects that the transmission is not shifting properly, a P0780 code will be stored and a malfunction indicator lamp (MIL) may be illuminated. On some models, this type of code will require multiple drive cycles in order for the MIL to be illuminated. In this case, the code may initially be exhibited as a pending code.
Symptoms & Severity
A P0780 transmission shift malfunction code should be addressed as urgent. A minor condition could morph into a catastrophic one if left unattended for an extended period of time.
Symptoms of a P0780 code may include:
Erratic transmission shift patterns Delayed transmission engagement Harsh transmission shifts (especially if the controller has been placed in limp-in mode) Transmission slippage Whining noise from the transmission pumpCauses
Potential causes for this code to set are:
Shorted or open circuits in the transmission control harness Low transmission fluid Outdated or burnt transmission fluid Defective shift solenoid/s Faulty input or output sped sensors Bad electronic pressure regulator Failed transmission pump Mechanical failure; including torque converter failure, clutch failure, or internal component wear/breakage A defective PCM or a PCM programming errorDiagnostic and Repair Procedures
You will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), a transmission pressure gauge, and a vehicle service manual (or All Data DIY) to diagnose a code P0780.
A careful visual inspection of the transmission and all related wiring harnesses is the best place to begin your diagnosis of this code. Pay particular attention to wiring that is routed near hot exhaust components and sharp edges. Keep in mind that a portion of the transmission control harness is located inside the transmission case. You may choose to wait and see if you must enter the transmission housing (for other purposes) to inspect this part of the harness. Interior transmission harnesses are prone to failure
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