P0035 OBD-II Trouble Code: Turbocharger or Supercharger Bypass Valve Control Circuit High

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Cost of diagnosing the P0035 code

P0035 is a diagnostic trouble code (DTC) for "Turbocharger or Supercharger Bypass Valve Control Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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P0025 trouble code definition

P0025 is the code for Turbocharger or Supercharger Bypass Valve Control Circuit High

What the P0025 code means

It is necessary to understand that each manufacturer has a slightly different definition for this code as it applies to their particular system. This generally means that there is a problem with the bypass system for the turbocharger or supercharger to relieve pressure either completely or partially, depending on how the system is designed.

For this P0025 code, the boost pressure is too high for proper engine operation and power

What causes the P0025 code?

Several things can cause the Check Engine Light to come on and require an OBD-II scanner to indicate this code:

  • Sensor input voltage signals to the engine control module (ECM) indicating a boost level that is more than 14 psi than specified by the manufacturer which will cause a code to be stored and a malfunction indicator lamp to be illuminated. The ECM recognizes this data as an inability to effectively control boost levels.

  • If the boost is more than 14 psi, it can indicate that pressure is not being sent through the bypass valve when it should be in order to relieve pressure.

  • The bypass valve is either stuck shut or not functioning properly.

What are the symptoms of the P0025 code?

  • The ECM detects the bypass valve control circuit has a high current condition or a short circuit.

  • The ECM cannot control the bypass valve for the turbo or supercharger.

  • The engine may have loss of power.

  • The Check Engine Light will come on once the ECM detects the high current condition.

How does a mechanic diagnose the P0025 code?

  • A mechanic will verify the code with an OBD-II scanner, then the mechanic should reset the code and road test the vehicle to determine if the Check Engine Light comes back on and if the P0025 code returns.

  • Depending on the manufacturer, a boost pressure gauge test will need to be determined to see if the boost pressure is within the manufacturer's recommended range.

  • If the pressure is too high, an inspection of the bypass valve and a pressure test must be done. Some bypass valves are spring operated and others, especially Asian models, are diaphragm operated with an electric sensor and control system.

Common mistakes when diagnosing the P0025 code

  • The most common mistakes on this code are related to not following test procedure and assuming basic components are operating normally.

  • Often a pressure sensor on the intake may be faulty and indicates high pressure sent to the ECM.

  • Do not replace the bypass valve, turbocharger, or supercharger unless it is clearly at fault.

How serious is the P0025 code?

This code requires absolutely immediate attention and should be diagnosed as soon as possible. The vehicle will still run but serious damage can occur to the engine if the problem is not repaired, and if the pressure is too high engine damage due to a too lean fuel mixture may occur.

Often times, if the Check Engine Light came on immediately at start up, the OBD- II system can be reset and the vehicle will operate normally.

What repairs can fix the P0025 code?

The most common repairs to address the P0025 code are as follows:

  • Have a certified technician verify the code with an OBD-II scanner, reset the fault codes, and perform a road test.

If the P0025 code returns, then follow the test procedure:

  • Do a pressure test on the intake system between the turbocharger and intake throttle valve. This will verify if the pressure is too high as specified by the manufacturer.

  • If the pressure is too high, check the bypass valve to determine if it is slightly or completely closed which will allow boost pressure to build excessively. This may require changing the bypass valve or the actuator with diaphragm.

  • If the pressure test is in the normal range as specified by the manufacturer, the pressure sensor may be faulty.

Having had this code before, it has been generally a problem with the bypass valve or waste gate stuck shut. If it is a spring loaded type, exhaust debris sticks the valve so it cannot open when the pressure increases beyond the specified maximum boost. If it is the diaphragm type, the diaphragm fails on the pressure operated servo and can be replaced separately from the turbo charger unit.

This problem is not normally a problem with the turbocharger itself. Newer cars emission systems recycle heavy carbon and oil mist from the crankcase directly into the intake and some bypass valves get clogged up similar to modern intake manifolds.

Additional comments for consideration regarding the P0025 code

Many vehicles with mileage over 100,000 have momentary sensor problems that usually occur during start up or prolonged stress situations on the drive train.

If the Check Engine Light comes on and the vehicle seems to be operating normally, the OBD-II system can be reset using the scanner and the problem may not reoccur. This is why it is important to verify the fault and reset it before doing any repairs.

Need help with a P0025 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6220.

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