Technical Description of OBD-II Trouble Code
Exhaust Gas Recirculation B Flow
What does that signify?
This is a generic powertrain diagnostic trouble code (DTC) that typically applies to OBD-II vehicles equipped with an exhaust gas recirculation (EGR) system. This may include vehicles from various manufacturers such as Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
A stored code P049A indicates that the powertrain control module (PCM) has detected a malfunction in the exhaust gas recirculation (EGR) system “B” flow for a particular step-down setting. The designation “B” refers to a specific position of the step-down EGR valve. An electrical or mechanical problem can cause the code P049A to be stored.
An excessive or insufficient EGR flow can result in the code P049A being stored.
The step-down EGR valve system plays a critical role in reducing the release of nitrous oxide (NOx) particles into the atmosphere during internal combustion and diesel engine operation. NOx has been identified as a contributing factor to ozone depletion from exhaust emissions. NOx emissions are regulated by federal mandate in North America.
The step-down EGR system is designed to recirculate a portion of the spent exhaust gases back to the intake manifold in measured increments. Once the exhaust gases are recirculated back to the intake manifold, they are burned a second time.
EGR system flow is monitored using various methods, including:
A code P049A will be stored and a malfunction indicator lamp (MIL) may illuminate if the PCM does not detect the desired degree of change from the respective “B” EGR flow monitoring sensor system. In some vehicle applications, multiple ignition cycles with a failure are required for MIL illumination.
Photo of an Exhaust Gas Recirculation (EGR) valve:
What is the severity of this DTC?
The conditions contributing to a code P049A can adversely affect overall engine performance and fuel efficiency. Therefore, it should be considered severe.
What are some of the symptoms of the code?
Symptoms of a P049A trouble code may include:
What are some of the common causes of the code?
Possible causes for this P049A engine code may include:
What are some P049A troubleshooting steps?
Start the diagnosis by locating the vehicle diagnostic connector and retrieving all stored codes with the scanner. Keep a record of this information in case it is needed during the diagnosis. Next, test-drive the vehicle to see if the code is immediately reset.
You may find a solution to your EGR system problems by searching vehicle technical service bulletins (TSB) for entries that match the vehicle, stored codes, and exhibited symptoms. TSB entries are derived from thousands of repair specialists and may contain valuable diagnostic hints.
If the P049A code is stored right after clearing the codes, you will need to access a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source.
Conduct a visual inspection of the EGR valve and all related wiring and connectors. Pay attention to wiring harnesses that are routed near hot exhaust manifolds and the sharp edges often associated with exhaust shields.
To prevent controller damage, disconnect all related control modules from the circuit before testing resistance/continuity with the DVOM.
Use the scanner to manually activate the EGR system. Most EGR systems require a certain rate of speed before automatic activation occurs. Use wiring diagrams and connector pinout charts from your vehicle information source to test each individual EGR valve connector circuit with the DVOM. Circuits that do not meet the manufacturer’s specifications will need to be traced back to the source, usually the PCM connector, and retested. If the output signal from the PCM is not detected, suspect a defective PCM or PCM programming error. Repair or replace open/shorted circuits as necessary.
If all circuits comply with the manufacturer’s specifications, use the DVOM to test the actual EGR valve and related sensors. Your vehicle information source will provide information for testing these parts. If the step-down EGR valve and/or any related sensors do not align with the manufacturer’s specifications, they should be replaced.
