Fault codeP0039

MODERATE

Turbo/Super Charger Bypass Valve Control Circuit Range/Performance

What this code means

Turbo/Super Charger Bypass Valve Control Circuit Range/Performance.

P0039 is a generic code: it means the same thing on every make. P0039 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 signal stays within its electrical limits, but its value is not plausible: it does not match what the control unit expects given the other sensors. The sensor may be drifting with age, but it may also be faithfully measuring a real mechanical problem — a leak, a blockage, an air leak. Replacing the sensor without checking does not always clear the fault.

Turbo bypass (diverter) valve

When you lift off the accelerator, the throttle closes while the turbo is still pushing air. The bypass valve opens to release that pressure back to the intake, which protects the turbo and keeps it spinning for the next acceleration. On many engines the control unit drives it with a solenoid.

What you notice

Turbo lag after a gear change, a fluttering or whistling noise when lifting off, sometimes a loss of boost if the valve stays open.

How to check it

Check the valve's connector and, on vacuum-operated versions, its small vacuum hoses. Diaphragm valves often fail with a torn membrane: a visual check after removal is enough. Klaro's intake pressure reading shows whether boost builds normally under load.

Watch it live in Klaro

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

Intake manifold pressure
Barometric pressure

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
39P0039