Understanding Error Code P049C: Excessive Flow Detected in EGR System “B”
Introduction
- What does the P049C code mean? (General definition: the PCM has detected excessive flow in the “B” circuit of the EGR system for a specific downgrade setting).
- This is a generic powertrain diagnostic trouble code (DTC) applicable to OBD-II equipped vehicles with an Exhaust Gas Recirculation (EGR) system.
- Examples of affected brands: Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
- Important: Precise repair steps may vary depending on the year, make, model, and powertrain configuration.
- The “B” designation refers to a specific position of the EGR valve in the downgraded state.
- An electrical or mechanical problem can cause the P049C code to be stored.
Downgraded EGR System Operation and Importance
- The downgraded EGR valve system is essential for reducing nitrogen oxide (NOx) emissions produced by the internal combustion of diesel engines.
- NOx contributes to the depletion of the ozone layer.
- NOx emissions are regulated by federal mandates in North America.
- The downgraded EGR system recirculates a portion of the exhaust gases to the intake manifold in measured increments for a second combustion.
EGR Flow Monitoring
- EGR system flow is monitored by different methods:
- DPFE Sensor (Differential Pressure Feedback EGR): Measures pressure in the tube connecting the EGR valve and the exhaust manifold. Valve opening increases pressure and sensor voltage.
- MAP Sensor (Manifold Absolute Pressure): In some applications, a proportional change in MAP sensor voltage is expected when the PCM commands the downgraded EGR to open to a certain level.
- MAT Sensor (Manifold Air Temperature): Some vehicles use the MAT sensor to detect the temperature increase when hot exhaust gases recirculate into the intake manifold.
- The P049C code is stored and the Malfunction Indicator Lamp (MIL) may illuminate if the PCM does not detect the expected change from the “B” EGR flow monitoring sensor system, indicating an excessively high flow.
- Several ignition cycles with the fault may be required for the MIL to illuminate on some vehicles.
Severity of DTC P049C
- Conditions contributing to a P049C code can affect overall engine performance and fuel efficiency.
- This code should be classified as severe.
Possible Symptoms of Code P049C
- List of associated symptoms:
- Decreased engine performance
- Excessively rich or lean exhaust
- Delayed engine starting (especially when cold)
- Reduced fuel efficiency
Common Causes of Code P049C
- List of possible causes:
- Faulty EGR valve
- EGR passage(s) clogged with carbon deposits
- Collapsed or cracked DPFE hoses
- Faulty DPFE, MAP, or MAT sensor
- Open or shorted circuits to the EGR valve or associated sensors
P049C Troubleshooting Steps
- Step 1: Retrieving codes and freeze frame data:
- Start by locating the vehicle’s diagnostic connector and use a scanner to retrieve all stored codes.
- Note this information for future reference.
- Test drive the vehicle to see if the P049C code resets immediately.
- Step 2: Consulting Technical Service Bulletins (TSBs):
- Search the vehicle’s TSBs for entries matching the vehicle, stored codes, and symptoms. TSBs may contain helpful diagnostic tips from specialists.
- Step 3: Preparing tools and information:
- If the P049C code is stored after clearing, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information (wiring diagrams, component specifications).
- Step 4: Visual inspection:
- Visually inspect the EGR valve, all associated wiring, and connectors.
- Pay close attention to wiring harnesses located near hot exhaust manifolds and the sharp edges of heat shields.
- Step 5: Precautions before electrical testing:
- To avoid damaging control modules, disconnect all associated control modules from the circuit before testing resistance or continuity with the DVOM.
- Step 6: Testing manual activation of the EGR system:
- Use the scanner to manually activate the EGR system (note that most systems require a certain speed for automatic activation).
- Step 7: Testing EGR valve circuits:
- Using wiring diagrams and connector pinout charts (from your information source), test each circuit of the EGR valve connector with the DVOM.
- Circuits not matching manufacturer specifications must be traced back to their source (usually the PCM connector) and retested.
- If no PCM output signal is detected, suspect a PCM programming issue or a faulty PCM.
- Repair or replace open or shorted circuits as necessary.
- Step 8: Testing the EGR valve and associated sensors:
- If all circuits meet specifications, use the DVOM to test the EGR valve itself and the associated sensors (DPFE, MAP, MAT).
- Your vehicle information source will provide the testing procedures and specifications for these components.
- Replace the downgraded EGR valve and/or associated sensors if they do not meet manufacturer specifications.
- Important note: This code (P049C) should only appear on vehicles equipped with downgradable EGR valve systems.