Fault codeP0078

MODERATE

Exhaust Valve Control Solenoid Circuit (Bank 1)

What this code means

Exhaust Valve Control Solenoid Circuit (Bank 1).

“Bank 1” is the side of the engine that holds cylinder number 1; “Bank 2” only exists on V and flat engines. An in-line engine has a single bank.

P0078 is a generic code: it means the same thing on every make. P0078 belongs to family P00xx — Fuel and air metering, auxiliary emission controls. Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit has detected an electrical anomaly on this circuit without saying exactly which. Diagnosis starts with a visual check of the wiring and connector, then measuring the component — resistance, supply, ground — with a multimeter.

Variable valve timing (camshaft actuator)

Many engines can shift the timing of their camshafts while running, using an oil-pressure actuator (phaser) on the end of the camshaft, controlled by a solenoid valve. The control unit advances or retards the cams to balance power, consumption and emissions, and checks with the camshaft sensor that the position it asked for is reached.

What you notice

Rough idle, lack of power at low or high revs depending on the position the cam is stuck in, higher consumption; on some engines a rattle at start-up from the phaser.

How to check it

Oil is the first suspect: a low level, the wrong viscosity or sludge prevents the actuator from moving. Check the level and the service history, then the solenoid valve (its resistance, its connector, and its fine filter screen which can clog). The phaser itself and the timing chain come next.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Engine RPM
Timing advance
Calculated engine load

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
0Fuel and air metering, auxiliary emission controls
78P0078