P0039

What it means

P0039 is the generic SAE J2012 code for a range or performance fault in the control circuit of turbocharger or supercharger bypass valve A. The engine control unit commands the bypass valve and monitors the result, and it has seen the valve or its circuit fail to respond as expected, or boost behave differently from what the commanded valve position should produce. Which valve is 'A' and how it is monitored depends on the engine and model.

Symptoms

• Engine warning light on
• Loss of power or poor acceleration under load
• Boost lower or higher than expected
• Whistling, fluttering or hissing noises from the intake during throttle lift-off
• Hesitation or surging when accelerating
• Engine may enter a reduced-power (limp) mode

Possible causes

• Bypass (recirculation or blow-off) valve sticking, worn or mechanically failed, or its diaphragm splitlikely
• Vacuum or boost hose to the valve actuator leaking, split, disconnected or blockedlikely
• Wiring or connector fault in the valve control circuit, such as chafing, corrosion, high resistance or a poor earthlikely
• Faulty electric solenoid or actuator controlling the bypass valvepossible
• Boost leak elsewhere in the intake or charge-air system, or a fault in the boost pressure or manifold pressure sensor giving implausible readingspossible
• Carbon or oil contamination restricting valve movementpossible
• Engine control unit internal fault or outdated software calibration, where the manufacturer has identified it as a causerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting load, engine speed and boost at the time the fault set, and look for related boost, pressure sensor or wastegate codes.
2. Visually inspect the bypass valve, its vacuum or pressure hoses and the connector for damage, splits, oil contamination, looseness or corrosion.
3. Check the charge-air system for leaks, including pipes, clamps, intercooler and joints, using a visual check and a pressure test as the manufacturer specifies.
4. Check the valve moves freely and returns properly by hand or with a vacuum pump, where the design allows, and look for a split diaphragm.
5. With the connector unplugged, test the control circuit for supply voltage, earth, continuity and short circuits, and measure solenoid resistance against the manufacturer's specification.
6. Use a bi-directional scan function to command the valve and confirm it operates, listening for a click or watching for a boost change.
7. Compare live boost and manifold pressure readings with the commanded values and check the pressure sensors for plausibility.
8. Check for software updates or technical service bulletins for the specific model and engine before replacing the control unit.

How to fix

• Replace the bypass valve or its diaphragm if it is stuck, worn or leaking.
• Repair or replace split, loose or blocked vacuum and boost hoses and secure the connections.
• Repair damaged wiring, connectors or earth connections in the valve control circuit.
• Replace the faulty solenoid or actuator that controls the valve.
• Seal any boost leaks in the charge-air system and replace any faulty pressure sensor.
• Apply a manufacturer-issued software update only if an outdated calibration is a confirmed cause for that model.

Can I keep driving?

Nearby codes

• P0038GenericHO2S Heater Control Circuit High Bank 1 Sensor 2
• P003AGenericTurbocharger/Supercharger Boost Control A Position Exceeded Learning Limit