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P04A4 Exhaust Pressure Control Valve B Stuck Open

OBD-II Trouble Code Technical Description

Article by
Stephen Darby
Stephen Darby
ASE Certified Technician

Exhaust Pressure Control Valve B Stuck Open

What does that mean?

This is a generic powertrain diagnostic trouble code (DTC) and typically applies to OBD-II vehicles equipped. That may include but is not limited to vehicles from Dodge, Honda, Chevy, Ford, VW, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.

A stored code P04A4 means that the powertrain control module (PCM) has detected a malfunction in one of the exhaust pressure control (regulator) valves. Valve "B" typically indicates the problem has occurred in the bank of the engine which does not contain the number one cylinder but designs vary between manufacturers. In this case, the valve appears to be stuck in the open position.

Exhaust pressure (also called back pressure) regulators are used in turbocharged gasoline and diesel engines. Exhaust back pressure control valve operation is often similar to that of the throttle body. It uses an electronically controlled plate to restrict exhaust flow as determined by the PCM. There is also an exhaust back pressure control valve position sensor and/or an exhaust back pressure sensor.

Increased exhaust back pressure is used to elevate engine and engine coolant temperature faster. This can be especially helpful in very cold climates.

This is a basic, generic overview of exhaust pack pressure valve operation. Check specifications for the vehicle in question before making any assumptions. When the PCM detects a cold air intake temperature that is below a minimum threshold, it will initiate exhaust back pressure valve operation and maintain it until the intake air temperature is normalized. Exhaust back pressure regulator activation usually only occurs once per each ignition cycle. The exhaust back pressure control valve is designed to park in the wide open position once it is deactivated by the PCM.

If the PCM detects that the exhaust back pressure regulator is not in the desired position, or if the exhaust back pressure sensor indicates that it is out of position, a code P04A4 will be stored and a malfunction indicator lamp (MIL) may be illuminated.

What is the severity of this DTC?

Since exhaust back pressure may affect climate control and drivability functions, a stored code P04A4 should be addressed with a certain degree of urgency.

What are some of the symptoms of the code?

Symptoms of a P04A4 trouble code may include:

What are some of the common causes of the code?

Causes for this P04A4 code may include:

What are some P04A4 troubleshooting steps?

A reliable vehicle information source will be required to diagnose a code P04A4. Other tools needed:

  1. A diagnostic scanner
  2. A digital volt/ohmmeter (DVOM)
  3. An infrared thermometer with a laser pointer

After a careful visual inspection of system related wiring and connectors, find the vehicle diagnostic port. Connect the scanner to the port and retrieve all stored codes and freeze frame data. Write this information down because it may be helpful as your diagnosis proceeds.

Now, clear the codes and test drive the vehicle to see if the P04A4 immediately returns. If there are intake air temperature codes or engine coolant temperature codes present, diagnose and repair those before attempting to diagnose the P04A4.

Search technical service bulletins (TSB), which apply to the vehicle, codes, and symptoms in question. If you find one that matches, it will likely aid you greatly in your diagnosis.

You may use the infrared thermometer to gain an actual exhaust temperature reading if no scanner data display is available. This could prove helpful to determine whether the exhaust pressure control valve is actually functioning or not. It may also detect a valve that is stuck in either the open or closed position.

Related P04A4 DTC Discussions

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