P04AA OBD Error Code: Problem & Solutions

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P04AA is a diagnostic trouble code (DTC) for “Exhaust Pressure Control Valve "B" Position Sensor/Switch Circuit Intermittent/Erratic”. It is a generic diagnostic trouble code which applies to all OBD-II vehicles equipped with an exhaust pressure control valve sensor or switch. In this article "B" indicates the problem is with a portion of the system circuit, instead of a particular symptom or component. Code P04AA is set when the PCM detects an intermittent problem with the exhaust pressure control valve circuit.

OBD-II Code Powertrain Control Module (PCM) failure is defined as a Exhaust Pressure Control Valve "B" Position Sensor/Switch Circuit. Powertrain Control Module (PCM) monitors the Exhaust Pressure Control Valve Position Sensor. Exhaust pressure control valve is used to adjust the back pressure during cold weather which actually helps in increasing the temperature of cabin. PCM usually uses the information from exhaust back pressure sensor and intake air temperature sensor to govern the control of the valve. If the engine control module (PCM) determines there is an incorrect signal from the Exhaust Pressure Control Valve, the PCM will set code P04AA.

What causes this problem with the Exhaust Pressure Control Valve "B" Position Sensor/Switch Circuit Intermittent/Erratic?

• Faulty exhaust pressure control valve
• Poor electrical connection or wiring issue
• Faulty PCM

1. Powertrain Control Module - A powertrain control module, abbreviated PCM, is an automotive component, a control unit, used on motor vehicles. It is generally a combined control unit, consisting of the engine control unit (ECU) and the transmission control unit (TCU). However, it is rare that PCM fails but if it happens repair or replace it immediately.
2. Exhaust Pressure Control Valve - The exhaust pressure control valve detects changes in the pressure of the exhaust gases to properly control the flow of exhaust gases through the EGR system. If it is malfunctioned can cause various problems so make sure it should work efficiently.
3. Exhaust Pressure Sensor - The Exhaust Gas Pressure Sensor is a Differential Sensor measuring the pressure difference between gas in the intake and the outtake of the Particulate Filter. Replace it if in case you discover it faulty.

Some common symptoms for this trouble code P04AA are below mentioned. If you discover any one of them, kindly take your vehicle to the reputed repair facility.

• Enhanced emissions
• Bad engine performance
• Difficulty in starting
• Illuminated check engine light

It is always suggested to resolve the stored trouble codes as soon as possible because at initial stage, you might not face any drivability issues but in a short span of time it can create major problems. Below mentioned are some repairs and replacements which might help you to resolve this code:

• Replace the faulty exhaust pressure valve
• Inspect the wiring and connections carefully and repair or replace the damaged ones
• Repair the open or shorted circuits
• Replace the failed PCM (rare)

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To avoid any mistakes while diagnosing this code, it is always recommended to have your vehicle diagnosed with the help of qualified technician. Steps to diagnose this code are as follows:

• Check the exhaust pressure control valve and corresponding wiring.
• Look for loose connections, damaged wiring, etc.
• Consult the factory wiring diagrams to determine which wires are which.
• Check the internal resistance of the solenoid.
• With the vehicle ignition on, use a digital multimeter set to DC volts to check for power at the solenoid (usually 12 volts).
• If there is not a reference voltage from the PCM, the PCM is probably faulty. However, PCMs rarely go bad.
• Connect the meter between the solenoid ground terminal and chassis ground. If the meter reads a numeric value, there is continuity. If the meter reads out of limits (OL) there is an open circuit between the PCM and solenoid that will need to be located and repaired.

Common Mistakes When Diagnosing the P04AA Code

Common mistakes while diagnosing this trouble code P04AA are unnecessary and expensive replacements which usually happen when one doesn’t follow all the steps carefully.