Code Definition

P0078 — Exhaust Valve Control Solenoid Circuit (Bank 1)

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

About P0078

P0078 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.

When P0078 is stored, the module has detected a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine.

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 P0078 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 P0078 code indicates a malfunction in the control circuit of the exhaust valve control solenoid for Bank 1. This solenoid is a key component in the engine's variable valve timing (VVT) system, which regulates the timing and lift of the exhaust valves. The Engine Control Module (ECM) sets this code when it detects an issue within the electrical circuit controlling the solenoid, affecting the engine's ability to efficiently manage exhaust valve operation.

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