P0078
Exhaust Valve Control Solenoid Circuit Bank 1
Generic electrical fault on the exhaust-valve control solenoid for bank 1. The exhaust control valve modulates exhaust backpressure or routing (EGR feed, sound, regen support); a malfunction shifts torque mapping and may trigger limp mode.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Solenoid coil failedCommon
Parts involved
- Exhaust Valve Solenoid
- Solenoid Wiring
P0078 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.