P004E OBD-II Trouble Code: Turbocharger/Supercharger Boost Control “A” Circuit Intermittent/Erratic

P004E code definition

The P004E trouble code signals an electrical malfunction with the turbocharger or supercharger boost control “A” circuit

What the P004E code means

The P004E code is a standard OBD-II trouble code that detects an issue with the turbocharger or supercharger boost control “A” circuit, with the “A” referring to a specific area of the control circuit. The boost levels in the unit are controlled by the powertrain control module (PCM), which relies on sensor input voltage signals from the turbocharger. When the PCM notes that these signals are abnormal (in general when the boost level is lower than nine pounds, or higher than 14 pounds) then the boost level likely cannot be controlled, and the PCM will store the P004E trouble code.

What causes the P004E code?

Many different things can cause the P004E trouble code, such as:

  • Vacuum leak in the intake manifold
  • Westgate is stuck open, or stuck closed
  • Dirty or defective air cleaner
  • Faulty boost sensor
  • Defective intercooler
  • Loose flange between the turbocharger and the intake pipe
  • Turbo failure, which is usually caused by oil leaks or restrictions
  • Damaged or loose hardware between the exhaust manifold and the turbocharger
  • Defective electrical components in the boost sensor circuit, such as wires, connectors, or fuses

What are the symptoms of the P004E code?

When the P004E trouble code is detected, the Check Engine Light will likely illuminate on the dashboard. There will usually be a handful of drivability issues as well, as it is common for the turbocharger or supercharger to experience greatly diminished performance. This may result in weak acceleration, an abnormally smoky exhaust system, and unfamiliar noises from the turbocharger, among other symptoms. If the vehicle has a boost pressure gauge, then it will likely display excessive pressure levels, and both the engine and transmission may run at an extremely high temperature. It is possible for cylinder detonation to take place as well.

How does a mechanic diagnose the P004E code?

The P004E code will be diagnosed using a standard OBD-II trouble code scanner. A reputable technician will use the scanner to view the freeze frame data for the code, and to check for the presence of additional codes. If the mechanic notes multiple trouble codes, then they should be addressed in the order in which the scanner shows them. The codes will then need to be reset, and the vehicle restarted, so the mechanic can see if the P004E code remains detected. If it does not, then an intermittent error or an incorrect trigger are likely to blame.

If the code remains detected, then the mechanic should start by visually inspecting the electrical components in the turbocharger or supercharger. All loose or corroded connectors, short or open wires, and blown fuses will require replacement. The wastegate will then be visually inspected, to see if it is stuck in the open or closed position, and then the air cleaner will be checked by the technician. Following these visual inspections, all hardware (such as clamps and bolts), hoses, sensors, and intakes will require inspection. If these inspections do not yield a solution, then a deeper diagnosis of the turbocharger or supercharger system is in order.

After any components are replaced, the mechanic should reset the codes and restart the vehicle, and check again for the presence of the P004E code. By doing this, the technician will know when the issue is fixed.

Common mistakes when diagnosing the P004E code

The most commonly made error when diagnosing the P004E code comes from not adhering to the OBD-II diagnosis protocol. It is vital that mechanics follow the protocol at all times, as it helps guarantee an efficient inspection that is devoid of erroneous repairs.

Turbochargers and superchargers are often replaced unnecessarily, when only one of their components was defective.

How serious is the P004E code?

The P004E trouble code will rarely keep a vehicle from being drivable, though there will be serious drivability issues. Failure to address the code can result in extreme damage to the transmission and engine, so an inspection should be scheduled as soon as the code is noticed.

What repairs can fix the P004E code?

Common repairs for the P004E code include:

Additional comments for consideration regarding the P004E code

The P004E trouble code only applies to vehicles that have turbochargers or superchargers. It is very common for this code to be joined by engine misfire or knock sensor trouble codes.

Need help with a P004E 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.


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