P0033 OBD-II Trouble Code: Turbocharger or Supercharger Bypass Valve Control Circuit

P0033 trouble code definition

P0033 is the code for Turbocharger or Supercharger Bypass Valve Control Circuit

What the P0033 code means

Each manufacturer has a slightly different definition for this code as it is relative to their particular system. This generally means 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.

What causes the P0033 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) that indicate a boost level reading less or greater (normally less than 9-psi or more than 14-psi) than specified by the manufacturer. This will cause a code to be stored and a malfunction indicator lamp to be illuminated. The ECU recognizes this data as an inability to effectively control boost levels and proper engine operation.

• If the boost is less than 9 psi, it can indicate that pressure is being sent through the bypass valve when it should not be open.

• The turbocharger plumbing may have a leak, reducing the boost pressure to the intake system.

• If the boost is more than 14 then pressure is not being relieved through the bypass valve.

What are the symptoms of the P0033 code?

• The Check Engine Light will come on.

• The ECM detects the bypass valve control circuit is intermittent and fails to work sometimes.

• The ECM will not be able to control the bypass valve and the turbo or supercharger will work erratically, causing loss of power or jerking during acceleration.

How does a mechanic diagnose the P0033 code?

• A mechanic will verify the code with an OBD-II scanner, then he should reset the code and road test the vehicle to determine if the Check Engine Light comes back on and the P0033 code returns.

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

• If the pressure is too low, an inspection of the intake hoses and pipes must be done to find leaks.

• If the pressure is too high, a diagnosis of the bypass valve should be done. The bypass valves are operated differently depending on the manufacturer. Some are spring operated and others, especially Asian models, are diaphragm operated with an electric sensor and control system.

Common mistakes when diagnosing the P0033 code

• The most common mistake for this code is related to assuming that basic components are operating normally.

• Commonly, this issue is related to intake leaks, after the turbocharger to the intake throttle valve. Often there is just a hose or clamp loose which is causing a loss of pressure.

• Do not replace a turbocharger or supercharger unless it is clearly at fault.

How serious is the P0033 code?

This code requires 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, especially if the boost exceeds the manufacturer's specifications.

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 P0033 code?

The most common repairs to address the P0033 code are as follows:

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

If the P0033 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 low or too high as specified by the manufacturer.

• If the pressure is too low, check the intake hoses, intercooler, pipes, and clamps for cracks, being loose, or damage. If they are correct, then check the bypass valve to determine if it is slightly or completely open allowing boost pressure to escape.

• If the pressure is too high, check the bypass valve to ensure it will open under maximum boost pressure as per the manufacturer's specifications. This is generally going to require replacing the valve or possibly the actuator on the diaphragm operated system.

• If the pressure is in the normal range as indicated by the manufacturer, the pressure sensor is faulty.

I've seen code P0033 come up several times when the Check Engine Light comes on. I experienced erratic boost pressure and verified it with a pressure gauge. I could not get it above 12 psi and the manufacturer specification was 15 psi maximum for normal operation. It was hard to determine the problem with just the engine running, so I put a longer hose on the pressure gauge to allow me to watch it while I drove the vehicle.

Driving seemed normal until it reached 12 PSI under load and then lost boost entirely. I did a careful inspection of the hoses, clamps, and intercooler when I found a plastic clamp on the intercooler inlet hose was actually broken but I could not see it until I pulled on it. The slip on connection from the hose to the intercooler was holding under low pressure because of the ribs on the intercooler inlet which would start leaking pressure at 12 psi since the clamp could not hold the higher pressure.

Now I carefully inspect every hose clamp even if it looks good, by trying to move it. I discovered that as hoses get older and exposed to high heat, they shrink on the inside and outside diameters which allows the clamps to loosen by themselves. This is why many manufacturers and motorsports teams use spring loaded hose clamps with lock nuts to ensure they will not blow off.

Additional comments for consideration regarding the P0033 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.

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