Exhaust Pressure Control Valve B Stuck Open
What Does It Mean?
This is a generic diagnostic trouble code (DTC) for the powertrain and generally applies to OBD-II equipped vehicles. This 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 the 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 valves (regulator). The “B” valve typically indicates that the issue occurred in the engine bank that does not contain cylinder number one, but designs vary by manufacturer. In this case, the valve appears to be stuck in the open position.
Exhaust pressure regulators (also called back-pressure) are used in turbocharged gasoline and diesel engines. The operation of the exhaust back-pressure control valve is often similar to that of a 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 raise engine and coolant temperature more quickly. This can be particularly useful in very cold climates.
This is a basic generic overview of how the exhaust pressure group valve operates. Check the specifications of the vehicle in question before making assumptions. When the PCM detects a cold air intake temperature below a minimum threshold, it initiates the operation of the exhaust back-pressure valve and maintains it until the intake air temperature normalizes. The activation of the exhaust back-pressure regulator typically only occurs once per 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 it is out of position, a P04A4 code will be stored and a Malfunction Indicator Light (MIL) may illuminate.
How Severe Is This DTC?
Since exhaust back-pressure can affect climate control and driving functions, a stored P04A4 code 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:
Delayed engine warm-up
Engine stalling or stumbling when cold
Reduced cold engine performance
Other exhaust back-pressure codes
What Are Some Common Causes of the Code?
Causes
of this P04A4 code may include:
Faulty exhaust back-pressure control valve position sensor
Bad exhaust pressure sensor
Defective exhaust pressure control valve
Open or shorted wiring in any of the exhaust pressure control valve circuits
What Are the P04A4 Troubleshooting Steps?
A reliable source of vehicle information will be needed to diagnose a P04A4 code. Other necessary tools:
A diagnostic scanner
A digital volt/ohmmeter (DVOM)
An infrared thermometer with a laser pointer
After a careful visual inspection of the wiring and connectors related to the system, locate the vehicle’s diagnostic port. Connect the scanner to the port and retrieve all stored codes and freeze frame data. Note this information, as it may be useful during your diagnosis.
Now, clear the codes and test-drive the vehicle to see if the P04A4 returns immediately. If there are intake air temperature codes or engine coolant temperature codes, diagnose and repair them before attempting to diagnose the P04A4.
Look for Technical Service Bulletins (TSBs) that apply to the vehicle, the codes, and the symptoms in question. If you find one that matches, it will likely help you greatly in your diagnosis.
If no obvious wiring or connector issues are discovered, start by testing the expected voltage signal at the exhaust pressure control valve (with the DVOM). You may need to use the scanner to simulate a cold start condition and activate the exhaust pressure control system.
If the proper voltage/ground signal is not detected at the exhaust pressure control valve connector, disconnect all associated controllers and use the DVOM to test the resistance and continuity of the individual circuit. Circuits found to be out of specification must be repaired or replaced.
If the correct degree of voltage/ground is found at the exhaust pressure control valve, follow the manufacturer’s recommendations for testing the exhaust pressure control valve (using the DVOM). If the exhaust pressure control valve pinout test does not match the manufacturer’s specifications, it must be replaced.
If the exhaust pressure control valve and circuits are functioning, test the exhaust pressure control valve position sensor or the exhaust pressure sensor (as applicable) according to the manufacturer’s specifications. Replace faulty components as necessary.