P049B Exhaust Gas Recirculation B Flow Insufficient Detected
OBD-II Trouble Code Technical Description
Exhaust Gas Recirculation B Flow Insufficient Detected
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) that typically applies to OBD-II vehicles that have an exhaust gas recirculation (EGR) system. That may include but is not limited to vehicles from Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
A stored code P049B means 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 certain position of the step-down EGR valve. Either an electrical problem or a mechanical problem may cause a code P049B to be stored.
The step-down EGR valve system is critical in the reduction of nitrous oxide (NOx) particles that are released into the atmosphere as a result of internal combustion and diesel engine operation. NOx has been proven to be a contributing factor in ozone depletion from exhaust emissions. NOx emissions are regulated by federal mandate in North America.
The step-down EGR system is designed to deliver a portion of spent exhaust gases back to the intake manifold, in measured increments. Once exhaust gases are re-circulated back to the intake manifold, they are burned a second time.
EGR system flow is monitored using one of several diverse methods, including:
The differential pressure feedback EGR (DPFE) sensor is positioned in or near the tube which connects the EGR valve and the exhaust manifold. When the EGR valve is opened, pressure in the EGR tube and DPFE sensor is increased. DPFE sensor voltage reflects the change accordingly The manifold absolute pressure (MAP) sensor is used to monitor EGR flow in other vehicle applications. In this type of system, when the PCM commands the step-down EGR opened to a particular stage, a proportionate change in MAP sensor voltage is also expected Some vehicles use the manifold air temperature (MAT) sensor to monitor EGR flow. When the EGR is opened to the desired amount (and hot exhaust gases are allowed to flow into the intake manifold), an appropriate variation in MAT sensor voltage is expectedA code P049B will be stored and a malfunction indicator lamp (MIL) may be illuminated if the PCM fails to see the desired degree of change from the respective "B" EGR flow monitoring sensor system. In this case, there is a detected below 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?
Overall engine performance and fuel efficiency may be adversely affected by the conditions which contribute to a code P049B. It should be categorized as severe.
What are some of the symptoms of the code?
Symptoms of a P049B trouble code may include:
Decreased engine performance Excessive rich or lean exhaust Delayed engine start-up (especially when cold) Diminished fuel efficiencyWhat are some of the common causes of the code?
Causes for this P049B engine code may include:
Defective EGR valve Carbon clogged EGR passage/s Collapsed or cracked DPFE hoses Faulty DPFE, MAP, or MAT Sensor Open or shorted circuits to the EGR valve or related sensorsWhat are some P049B troubleshooting steps?
Begin your diagnosis by locating the vehicle diagnostic connector and retrieving all stored codes with the scanner. Record this information in case you need it as the diagnosis unfolds. Now, test-drive the vehicle to see if the code is immediately rese
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