Code Definition

P078C — Shift timing solenoid B stuck On

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

About P078C

P078C 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 P078C 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 P078C fault code is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects that shift timing solenoid B is stuck in the on position. This condition implies that the solenoid, which is responsible for controlling the flow of hydraulic fluid in the transmission to aid in gear shifts, is continuously active or open, regardless of the control commands. When the solenoid is stuck on, it can lead to continuous fluid flow, potentially causing issues with gear engagement, shift timing, and overall transmission performance.

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