Code Definition

P078E — Transmission mode switch signal error

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P078E

P078E is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P078E is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The P078E fault code is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects an error in the signal from the transmission mode switch. This switch allows the driver to select different transmission settings, such as sport mode, economy mode, or manual shift mode, which alter how the transmission behaves. An error in the switch signal suggests a problem with the switch's function or its communication with the control modules. This could lead to the transmission being unable to switch modes correctly or respond to driver inputs as intended.

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