Code Definition

P078B — Shift timing solenoid B stuck off

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

About P078B

P078B 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 P078B 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 P078B fault code is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects that the shift timing solenoid B is stuck in the off position. This solenoid is integral to the transmission’s shifting mechanism, controlling the flow of hydraulic fluid to facilitate gear changes. When the solenoid is stuck off, it fails to activate when commanded, resulting in inadequate control of the fluid flow necessary for proper gear engagement. This condition may lead to issues in shift timing and can affect the overall performance of the transmission.

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