P04A4 - OBD Trouble Code

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Is there a block between the exhaust manifold and the pressure sensor? Are there any leaks? Is your PCM damaged? Then it’s more likely that your system will show the code P04A4. A fault in the OBD-II Code Powertrain Control Module (PCM) can arise if the Exhaust Pressure Control Valve "B" is Stuck Open

As the motor of the vehicle warms up, the Exhaust Pressure Control valve manages the exhaust back pressure. If an incorrect or broken signal is identified by the engine control module (PCM) from the Exhaust Pressure Control Valve, P04A4 error code will be set by the PCM.

Exhaust Back Pressure Regulator is an adjustable valve which controls exhaust back pressure through cold ambient temperatures to raise the cab heat and minimize the time needed to unfreeze the windshield. The Engine Control Module (ECM) utilizes the measured exhaust back pressure, (ambient) intake air temperature, oil temperature of engine and load of engine to decide the preferred exhaust back pressure. Valve position is organized by turning the output signal circuit to 12 volts inside the ECM. On/off time is modified from 0 to 99 % depending on the preferred exhaust back pressure. During each engine start-up, the ECM exercises the exhaust back pressure valve and commands it to on and off once. During the start-up of engine, if the Engine Oil Temperature (EOT) sensor senses the oil temperature sensor that is sensed by between 32°-140°F (0-60°C), and the Intake Air Temperature (IAT) sensor senses the intake air that is < 37°F (5°C), then the valve of the back pressure will continue to be half shut. As the oil temperature rises during the operation of the engine, the ECM will control the valve in response to the rising temperature of the oil.

What causes this problem with the Exhaust Pressure Control Valve "B" Stuck Open

• Obstruction in the tube between the exhaust manifold and the pressure sensor
• A leak in the Exhaust system / Air Inlet / Charge Air
• Opening in the ground circuit to the exhaust pressure sensor
• Opening in the signal circuit from the exhaust pressure sensor to the PCM (powertrain control module)
• Short supply of voltage from the signal circuit to the exhaust pressure sensor
• Exhaust Gas Pressure Sensor or over boosting the turbocharger
• Possibly the PCM is unsuccessful

1. Powertrain Control Module - A failure in the powertrain control mode can give rise to this error code. Change the damaged parts immediately.
2. Exhaust Pressure Control Valve - A mistake in the exhaust pressure control value can create mishaps. Rectify/ repair the valves immediately.
3. Exhaust Pressure Sensor - Check if your exhaust pressure sensor is similar to your manufacturer’s specification. If not so, you can get them easily at Parts Avatar.
4. Engine Control Module - Any error in the engine control module has to be checked and if the part is damaged change is immediately.
5. Exhaust Gas Pressure Sensor - Is there any leak in your vehicle’s exhaust gas pressure sensor. Repair the leaky area to avoid further trouble.
6. Exhaust system - If there are any other error codes or wiring issues in the exhaust system, restore it immediately

If you are facing OBD error code P04A4, then there are significant common symptoms that can be felt or observed. We have worked out a list here to help you out in understanding this problem better.

Common Symptoms

• Late engine warm up
• Engine stall or stumbling when the system is cold
• Reduced engine performance when cold
• Extra exhaust back pressure codes

It is very important to fix the fault code P04A4. So here are some ways with which you can correct this issue:

• Repair the Powertrain / Engine control module
• Fixing the exhaust pressure sensor / exhaust gas pressure sensor
• Changing the Exhaust pressure control valve / exhaust system

However, if you face any issue then we have stocked a wide range of best priced Powertrain Control Module, Exhaust Pressure Control Valve, Exhaust Pressure Sensor, Engine Control Module, Exhaust Gas Pressure Sensor, Exhaust system and more to help you out in fixing your car.

If you want to easily diagnose this P04A4 fault code, then all you have to do is to follow the steps which are mentioned below:

In order to diagnose the code P04A4 you will need a reliable vehicle information source. Other tools include:

• A diagnostic scanner
• A digital voltmeter / ohmmeter (DVOM)
• An infrared thermometer which has a laser pointer
• Find the diagnostic port of the vehicle once you carefully inspect the wires and connectors of the system. Link the scanner to the port and recover all stored codes and freeze the frame data. Note down this information as it may be helpful for your diagnosis to proceed.
• Before you test drive the vehicle, clear the codes and see if the P04A4 immediately returns. If you find any intake air temperature codes or engine coolant temperature codes, then diagnose and fix those parts before trying to diagnose the P04A4.
• Search for the technical service bulletins (TSB), which is applicable for the vehicle, codes, and symptoms in question. If you find any one related to your search, then it will greatly help you in diagnosing.
• If there is no issue with the wiring or connector, start testing the predictable voltage signal at the exhaust pressure control valve (with the DVOM). You have to use the scanner to activate a cold start condition and trigger the exhaust pressure control system.
• If the approximate voltage/ground signal is not found at the exhaust pressure control valve connector, you have to disconnect all the linked controllers and use the DVOM to test individual circuit resistance and continuity. Circuits that are non-compliant have to be repaired or replaced.
• If you detect the correct degree of voltage/ground at the exhaust pressure control valve, test the exhaust pressure control valve by following the manufacturer’s recommendations (using the DVOM). If the pin out test of the exhaust pressure control valve is not similar to manufacturer’s specifications, you have to replace it. If the exhaust pressure control valve and circuits are in good operating condition, then test the position of the exhaust pressure control valve or exhaust pressure sensor (as applicable) according to the specification of the manufacturer. Substitute the failed components as needed.
• If the display of the scanner data is not available, then use the infrared thermometer to gain the actual exhaust temperature reading. This can be helpful to detect if the exhaust pressure control valve is really functioning or not. It may also be helpful to detect a valve that is jammed either in the open or closed position.
• If there is a defect in the catalytic converter or muffler it will not cause the code P04A4 to be stored.
• Turbocharged / supercharged applications are mostly used in Exhaust pressure control systems.

Common Mistakes When Diagnosing the P04A4 Code

On diagnosing, you will see a few of the common mistakes like:

• A failed Exhaust pressure control valve
• Faulty Powertrain Control Module (PCM)
• Issue with wiring system