Technical Description of OBD-II Trouble Code
Excessive Detected Flow of Exhaust Gas Recirculation B
What does that signify?
This is a generic diagnostic trouble code (DTC) for powertrain that is commonly found in OBD-II vehicles with an exhaust gas recirculation (EGR) system. This includes vehicles from various manufacturers such as Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
While 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 P049C 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 P049C to be 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 emissions contribute to ozone depletion and are regulated by federal mandate in North America.
The step-down EGR system is designed to recirculate a portion of 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 P049C 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 this case, there is an excessive expected amount of flow. 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 P049C 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 P049C trouble code may include:
What are some of the common causes of the code?
Possible causes for this P049C engine code may include:
What are some P049C 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. Test-drive the vehicle to see if the code is immediately reset.
Search 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 P049C is stored right after clearing the codes, you will need 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 jagged edges often associated with exhaust shields.
Before testing resistance/continuity with the DVOM, disconnect all related control modules from the circuit to prevent controller damage.
Use the scanner to manually activate the EGR system. Most EGR systems require a certain rate of speed before automatic activation occurs. Test each individual EGR valve connector circuit (with the DVOM) using wiring diagrams and connector pin out charts from your vehicle information source. Circuits that do not conform to 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 are in compliance with 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 manufacturer’s specifications, they should be replaced.
