What does it mean?
This diagnostic code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996 and newer), although specific repair steps may vary slightly by model.
The P0239 code is generic in that it refers to a problem in the turbocharger/supercharger boost sensor A circuit. Although generic in nature, never assume it is identical for all vehicles.
OBD codes do not necessarily point to a specific component, but rather to an area where the technician can look for possible causes of a problem within that circuit, which could include multiple possibilities.
All vehicles with the P0239 code have one singular point in common. It refers to an unacceptable discrepancy between the ECM’s (Electronic Control Module) programmed percentage of turbo boost at a specific RPM and the sensor signal value. These two values must coincide within close limits.
How turbocharging (forced induction) increases performance
Turbochargers force much more air into the engine than the engine is capable of under normal aspiration conditions. The greater the volume of air forced into the cylinders, the greater the increase in fuel equates to increased power.
Typically, a turbocharger can increase power by 35 to 50% in an engine specifically designed for turbocharging. The components of a conventional engine will not withstand the stresses placed on it by forced induction.
Turbochargers offer high power gains with little to no negative effects on fuel economy. They use exhaust speed to propel the turbocharger, so it’s essentially free power. That’s the advantage. The disadvantage is that they take a beating and tend to fail at unpredictable times for a multitude of reasons. When an indication occurs that a problem with the turbocharger has happened, resolve it as soon as possible. A turbocharged engine greatly exaggerates engine problems due to the mass of compressed air.
Never tighten the wastegate and do not attempt to install any modification on a stock turbocharged engine to increase boost pressures. The fuel and timing curve of most engines will not adapt to boost pressures higher than normal and engine damage will occur.
Note: This DTC is basically identical to P0235 which refers to turbocharger “A”.
Symptoms
Symptoms of a P0239 diagnostic code may include:
The P0239 code will be set, which simply means a problem exists somewhere in this circuit preventing proper boost control. Additional progressive codes may be set regarding this malfunction, each relating to a section of the circuit.
The engine may lack acceleration.
The boost pressure gauge will indicate less than 9 pounds of boost or more than 14 pounds of boost. Both are out of range.
Unusual noises or rattling from the turbocharger or piping.
The engine knock sensor code may appear, indicating detonation due to high cylinder head temperatures.
The engine may exhibit a general lack of power.
Exhaust smoke.
Fouled spark plugs
Abnormally high engine temperature at cruising speeds.
Hissing noises at the wastegate
Causes
Turbochargers typically spin at an incredible speed of 100,000 to 150,000 RPM. They are not the most tolerant of imbalance conditions or lack of clean oil to the bearing.
Causes
potential causes of this DTC include:
Vacuum leak at the intake manifold
Dirty air filter
Faulty wastegate – stuck open, closed, or leaking
Insufficient oil supply to the main shaft bearing – obstruction in the oil supply or return line.
Bearing failure causing slow rotation due to drag.
The bearing wobbles and the turbine blades hit the turbo housing.
Chipped, twisted, or missing turbine blades, causing imbalance.
Oil seal leak on the compressor side of the turbo, as shown by oil in the turbo and fouled plugs.
Excessive axial play in the turbo
Faulty intercooler
Loose connections between the intake pipe and the throttle body
Cracks in the turbo housing
Loose exhaust manifold at the turbo bolts.
Poor electrical connection to the Turbo boost sensor.
Short or open in the sensor harness between the sensor and the ECM.
Faulty sensor or ECM 5-volt reference driver.
Diagnostic steps
and possible solutions
From my experience, the diagnostic flow starts with the most common turbo problems and works systematically down to the least likely. Simple tools are needed, such as a vacuum gauge and a dial indicator.
Confirm that the engine is running correctly, without faulty plugs and without codes related to a faulty knock sensor.
On a cold engine, inspect the clamps at the turbo outlet, the intercooler, and the throttle body for tightness.
Try to wiggle the turbo on the exhaust flange to see if it is tight.
Inspect the intake manifold for leaks of any kind, including intake hoses.
Remove the wastegate actuator. Operate the valve manually while checking for a sticky valve causing low boost.
Locate an unused vacuum port on the intake manifold and install a vacuum gauge. Start the engine. At idle, the engine should have between 16 and 22 inches of vacuum. If it has less than 16, the catalytic converter is bad and will not allow boost to build.
Quickly rev the engine to 5000 RPM and release the throttle while observing the vacuum gauge as it displays boost pressure. If the boost pressure exceeds 19 pounds of boost, you have a bad wastegate. If the boost does not rise between 14 and 19 pounds of boost, a problem exists with the turbo itself.
Stop the engine and let it cool. Remove the turbo outlet pipe and look inside the turbo to see if the blades are hitting the sides of the housing. Look for twisted or missing blades or oil in the turbo. Spin the blades by hand and look for grinding or resistance indicating a faulty turbo.
Inspect the oil lines from the engine block to the turbo center bearing and the return line from the bearing to the oil pan for leaks.
Install the dial indicator on the turbine output nose and move the turbo shaft in and out. If there is more than 0.003 axial play, the center bearing is faulty.
If the turbo passes these tests, it is good. Use the service manual to test the boost sensor and harness using a volt/ohmmeter. Locate the ECM’s 5-volt reference to the sensor and confirm the voltage. No voltage present indicates an open or short in the harness or a bad ECM.
Locate the appropriate reference signal from the boost sensor to the ECM and confirm a variable voltage as the RPM increases. No voltage rise indicates a bad sensor.