P004A OBD-II Trouble Code: Turbocharger/Supercharger Boost Control “A” Circuit/Open

Check Engine Light

P004A code definition

The P004A trouble code detects an issue with the turbocharger or supercharger boost control in the “A” circuit.

What the P004A code means

The P004A code is a generic OBD-II trouble code that notes a problem with the boost control in the “A” circuit for the turbocharger or the supercharger. In this case the “A” stands for a specific chamber in the turbocharger or supercharger, as opposed to an individual component. The turbocharger or supercharger sends boost level information to the powertrain control module (PCM) via sensor input voltage signals. When these signals tell the PCM that the boost level is notably lower or higher than the manufacturer’s suggested settings, then the PCM cannot properly command the boost levels, and the P004A code will be triggered. In general, this will occur when the boost level is less than nine pounds, or more than 14 pounds.

What causes the P004A code?

The P004A trouble code can be caused by numerous things, including:

  • Vacuum leak in the intake manifold
  • Damaged or dirty air cleaner
  • Malfunctioning boost sensor
  • Malfunctioning intercooler
  • Wastegate is stuck, in either the open or closed position
  • Loose flange in between the intake pipe and the turbocharger
  • Turbo failure (often the result of oil leaks and restrictions)
  • Loose or damaged hardware connecting the turbocharger to the exhaust manifold
  • Damaged or loose electrical components in the boost sensor circuit, such as loose wires or corroded connectors

What are the symptoms of the P004A code?

The P004A trouble code can be accompanied by a lot of symptoms. The turbocharger or supercharger will have decreased performance, which can result in lessened acceleration, hissing or rattling noises from the turbocharger, excessive smoke from the exhaust system, and other engine performance issues. It is also common for the engine or the transmission to be at a very high temperature, and if your vehicle is equipped with a boost pressure gauge you will notice extremely high pressure levels. In some cases, cylinder detonation may occur.

How does a mechanic diagnose the P004A code?

The P004A code should be diagnosed with the assistance of a standard OBD-II trouble code scanner. A trained mechanic will use the freeze frame data from the code scanner to analyze the P004A code, and search for other codes that may be present. The codes should then be reset and the vehicle restarted, to see if the codes persist. If the P004A code does not return, it is likely an erroneous detection.

If the P004A trouble code returns after being reset, then the mechanic should start with a basic inspection of the turbocharger or supercharger. This should begin with a visual inspection of all electrical components, such as wires, connectors, and harnesses. Next, the mechanic should check the wastegate to see if it is stuck, and then inspect the air cleaner for any signs of damage or dirtiness. If no issues are found, the turbo clamps, hoses, bolts, intakes, and sensors should be examined.

If the issue still has not been resolved, the mechanic will do a more detailed and thorough inspection of the turbocharger or supercharger system.

Whenever an issue has been noticed and resolved, the trouble codes should be reset and the vehicle restarted, to see if the P004A code has been fully resolved.

Common mistakes when diagnosing the P004A code

The most common error when diagnosing the P004A code comes from a failure to comply with the standard OBD-II trouble code diagnosis protocol. It is very important to adhere to the protocol step by step, as this ensures a proper inspection, diagnosis, and repair.

It is common for turbochargers to be replaced when there is a simple fix, such as new wires or connectors, or a simple wastegate repair.

How serious is the P004A code?

A vehicle with the P004A trouble code can still be driven, but there will be a very noticeable lack of engine performance. If a car is driven with the P004A code detected, it runs the risk of causing severe damage to the engine or the transmission. The vehicle should be inspected and repaired as soon as the code is detected.

What repairs can fix the P004A code?

Some repairs for the P004A trouble code include:

Additional comments for consideration regarding the P004A code

The P004A trouble code only exists in vehicles with turbochargers or superchargers. The code is often accompanied by other trouble codes, such as additional boost codes, knock sensor codes, and engine misfire codes.

In some vehicles the P004A code may be listed as the P0045 code.

Need help with a P004A 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 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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