P0240 Diagnostic Trouble Code: Turbocharger Boost Sensor “B” Circuit Range/Performance

Fault code P0240 is called “Turbocharger Boost Sensor “B” Circuit Range/Performance” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0240

OBD-II fault code P0240 is a generic fault, most often defined as an invalid “B” boost pressure sensor circuit signal. It is set when the Powertrain Control Module (PCM) detects a general fault in the boost induction control circuit.

P0240 Diagnostic Trouble Code: Turbocharger Boost Sensor "B" Circuit Range/Performance

Regardless of the specifics of the device used (turbocharger / supercharger). The goal is to increase the power output of the engine without using significantly more fuel. Although forced induction is widely used, this technology is particularly useful for small engines. Because it gives a huge increase in power at a relatively low cost. And also without significant losses in terms of weight and fuel consumption.

However, supercharger pressure needs to be controlled, both to maximize benefit and to protect the engine from the effects of excessive pressure. To do this, turbochargers use built-in mechanical devices to relieve excessive pressure. These devices are controlled electronically by the PCM, so the boost pressure, never exceeds the maximum allowable limit.

To effectively control the boost, the PCM uses primary input from the absolute manifold pressure (MAP) sensor. This value is then compared with input data from the engine speed sensor. It also uses the intake air temperature (IAT) and throttle position sensor (TPS).

If the charge control system is fully functional, the PCM will use the combined input from all of the sensors involved. However, if the boost control circuit fails, the PCM can no longer effectively control the boost pressure.

Therefore, code P0240 is set and a warning light will illuminate as a result. Note that depending on the nature of the problem, the PCM may also set additional codes. Some of which may cause it to go into failsafe or emergency mode. This is done as a precautionary measure as well as to protect the engine.

Symptoms of vehicle malfunctions

The main signal that an error P0240 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will illuminate (the code will be stored as a fault).
  2. There may be a loss of power due to engine turbocharger shutdown.
  3. Increased noise, there may also be ringing and rattling of the turbocharger or piping.
  4. Premature ignition, resulting in noticeable detonation.
  5. Ignition jerking/missing.
  6. Engine overheating with subsequent problems.
  7. Contamination of spark plugs.
  8. The engine may lack power during acceleration.

The severity level of fault code P0240 is medium, but it should be understood that when the turbocharger pressure increases, the engine power increases. If the turbocharger boost pressure sensor fails, the vehicle’s PCM may shut down the turbocharger. This will result in a drop in engine power.

Factors that can cause this error code

The error code P0240 can mean that one or more of the following problems have occurred:

  • The turbocharger boost pressure sensor is defective.
  • Damaged, burned, shorted, disconnected, corroded charge pressure sensor wires or connectors.
  • Short circuit or break in sensor wiring harness between sensor and PCM.
  • Damaged, broken, cracked, or displaced vacuum tubes.
  • Insufficient oil supply to the main shaft bearing.
  • Defective by-pass valve.
  • Bearing failure causing slow cranking due to resistance.
  • Nicks, bent or missing turbine blades causing imbalance.
  • Leaking oil seal on turbocharger compressor side.
  • Damaged or defective boost pressure relief device.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0240

Some suggested steps for troubleshooting and fix the error code P0240:

  1. Read all stored data and error codes with an OBD-II scan tool.
  2. Clear the error codes from the computer memory and test-drive the vehicle to find out if error P0240 appears again.
  3. Check the operation of the turbocharger boost pressure sensor by comparing its reading with the manifold absolute pressure sensor.
  4. Inspect the turbocharger boost pressure sensor for blockage.
  5. Test the connector and wiring for damage, looseness and corrosion.

Diagnose and repair of problems

Turbines typically spin at incredible speeds of 100,000 to 150,000 rpm. They are intolerant to imbalance or a lack of clean oil in the bearing.

The diagnostic process for the P0240 error is best started with the most common turbo problems. These will require tools such as a vacuum gauge and a dial gauge.

Checking the vacuum

Make sure the engine is running properly, with no ignition skips or codes related to a faulty detonation sensor. Then, check for leaks at the turbocharger outlet, intercooler, and throttle body.

Inspect the intake manifold for leaks of any kind, including vacuum hoses. Remove the lever from the throttle valve. Manually operate the valve, looking for a jammed valve causing a drop in boost.

Measuring boost pressure, turbocharger inspection

Locate the vacuum with no holes in the intake manifold and install a vacuum gauge. Start the engine. At idle the engine should have a vacuum of 1-1.5 atmospheres. If less than 1 atmosphere then the catalytic converter is defective and will not allow boost.

Quickly accelerate the engine to 5000 rpm and release the throttle, observing the vacuum gauge indicating the boost pressure. If the boost pressure rises above 1.3 atmospheres, then the bypass valve is bad.

Stop the engine and let it cool down. Remove the turbine exhaust hose and look inside to make sure the blades are not rubbing the housing. Look for bent or missing blades or oil in the turbocharger. Rotate the blades by hand, looking for resistance indicating turbocharger malfunction.

Inspect the oil lines from the cylinder block to the center bearing and the return line from the bearing to the oil pan for leaks. Place a dial gauge on the turbine outlet and rotate the turbine shaft. If the axial play exceeds 0.003, the center bearing is defective.

Sensor and wiring

If there is no problem after all the checks, but code P0240 is still present, check the electrical components. You need to test the boost sensor and wiring harness with a voltmeter. Make sure there is 5 volts coming to the sensor from the PCM to the sensor.

No voltage means an open or short in the wiring harness. The PCM may also be faulty. Locate the reference signal from the boost sensor to the engine control unit and see if the voltage changes as the RPM increases. No voltage spike indicates a faulty sensor.

On which vehicles does this problem occur most frequently

Fault code P0240 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chevrolet (Aveo)
  • Fiat
  • Ford
  • Honda
  • Hyundai (Solaris)
  • Kia
  • Mercedes-Benz
  • Mitsubishi
  • Nissan (Maxima)
  • Opel
  • Peugeot
  • Pontiac (Vibe)
  • Renault
  • Subaru (Forester)
  • Toyota
  • Volvo

Fault code P0240 can sometimes be found with other errors. The most common are the following: P0174, P0241, P0242, P0420, P0421.

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