P0078 — Exhaust Valve Control Solenoid Circuit Bank 1

P0078: Exhaust Valve Control Solenoid Circuit Bank 1 — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

Exhaust Valve Control Solenoid Circuit Bank 1. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • An engine warning can appear with reduced response or uneven running.
  • Fuel consumption may increase if the exhaust valve-timing control cannot operate normally.

Possible causes

  • Broken or shorted wiring, oxidized contacts or a loose connector in the bank 1 exhaust solenoid circuit.
  • A failed exhaust valve-timing control solenoid; controller faults are less common possibilities.

What to check

  • Confirm P0078 and locate the exhaust valve-control solenoid, bank 1, using the vehicle documentation.
  • Inspect solenoid connectors and wiring; check engine-oil condition if the mechanism uses hydraulic timing.
  • Test electrical continuity and commanded solenoid response using model-specific procedures before replacing hardware.

Also written as: P0078-00, P007800, PO078 (some scan tools add the fault-type byte, e.g. -00).