Technical Description of OBD-II Trouble Code
The vehicle has detected that there is insufficient flow in the exhaust gas recirculation (EGR) system.
What does that mean?
This is a generic diagnostic trouble code (DTC) that applies to OBD-II vehicles with an EGR system. This includes 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 P049B indicates that the powertrain control module (PCM) has detected a malfunction in the EGR system “B” flow for a specific step-down setting. The “B” designation refers to a particular position of the step-down EGR valve. An electrical or mechanical problem can cause this code to be stored.
The step-down EGR valve system is crucial in reducing the release of nitrous oxide (NOx) particles into the atmosphere during internal combustion and diesel engine operation. NOx emissions are regulated by federal mandate in North America due to their contribution to ozone depletion from exhaust emissions.
The step-down EGR system recirculates a portion of the spent exhaust gases back to the intake manifold in measured increments. These gases are then burned a second time.
EGR system flow is monitored using various methods, including:
A code P049B will be stored and the 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. This indicates a 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?
The conditions contributing to a code P049B 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 P049B trouble code may include:
What are some of the common causes of the code?
Possible causes for this P049B engine code may include:
What are some P049B troubleshooting steps?
Start the diagnosis by locating the vehicle diagnostic connector and retrieving all stored codes with a scanner. Record this information for reference 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 often provide helpful diagnostic hints based on the experiences of repair specialists.
If the P049B code is stored again after clearing the codes, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source.
Perform a visual inspection of the EGR valve, wiring, and connectors. Pay attention to wiring harnesses near hot exhaust manifolds and the sharp edges of 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 for automatic activation. Test each individual EGR valve connector circuit (with the DVOM) using wiring diagrams and connector pinout charts from your vehicle information source. Follow circuits that do not meet manufacturer’s specifications back to the source (usually the PCM connector) and retest. 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.
