Error Code P049C is defined as Exhaust Gas Recirculation B Flow Excessive Detected. This code is a generic trouble code, meaning it applies to all vehicles equipped with an OBD-II system with an EGR (Exhaust Gas Recirculation) system, particularly vehicles made since 1996 up to present. This includes but not limited to vehicles from Audi, Chevrolet, Dodge, Ford, Mazda, Mitsubishi, Nissan, Subaru, Toyota, and Volkswagen. Although generic, diagnostics and repair vary from one make and model to another, or from powertrain configuration.
When this code is stored, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a malfunction in the exhaust gas recirculation (EGR) system “B” flow for the specific step-down setting. The “B” refers to a certain position of the step-down EGR valve. This code can be caused by either electrical or mechanical problem.
Error Code P049C happens when the PCM fails to see the right degree of change of respective “B” EGR flow monitoring sensor system; in this case, this code means there is an extremely high amount of low as compared to the specifications set by the manufacturer. For some vehicles, it may require multiple ignition cycles (with failure) for this code to activate the Check Engine light.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include:
- Excessive rich or lean exhaust
- Decreased engine performance
- Increase in fuel consumption
- Delayed engine start-up (particularly obvious during cold)
Common causes for this code include:
- Faulty EGR valve
- Clogged carbon EGR passage(s)
- Cracked or collapsed DPFE hoses
- Defective DPFE (differential pressure feedback EGR), MAP (manifold absolute pressure), or MAF (manifold air temperature)
- Open or short circuit to the EGR valve or related sensors
How to Check
As with many codes, diagnosing this code requires the use of an OBD scanner to retrieve all the codes stored and all the information when the codes were stored. Then, the codes are reset and the vehicle will be taken for a test drive.
Many manufacturers provide a solution for EGR system problems in their TSB (technical service bulletin), so it pays to check them out as well. You can get this from various repair specialists, or even from your dealership.
Use the diagnostic scanner, DVOM (digital volt-ohmmeter), and vehicle information source if the code returns after you reset.
Proceed on visually checking the EGR valve, along with all related connectors and wirings. Check the wiring harness routed near hot exhaust manifolds and the jagged edges often associated with shields.
To prevent damage to the controller, disconnect all control modules related to the circuit before testing the resistance or continuing with the DVOM.
Activate the EGR manually through the scanner. Many EGR will usually require a certain rate of speed before the automatic activation happens. Then, locate the vehicle information source through the vehicle’s wiring diagram and connector pin out charts. Test every EGR valve connector circuit using the DVOM. Circuits that don’t follow specifications set by the manufacturer must be followed back to the source (usually the PCM connector) and retested. If there is no output signal from the PCM, then the PCM must be defective, or its program must be at fault. For this, you will have to repair or replace open/shorted circuits as required.
Test the EGR valve and related sensors using the DVOM to see if all circuits comply with the manufacturer’s specifications. Your vehicle information source will once again yield information for testing these parts. If the step-down EGR valve and any related sensors do not align with manufacturer’s specifications, they should be replaced.
How to Fix
Common repairs for this code are:
- Repair or replacement of fault in the wiring, connectors, and harness
- Replacement of step-down EGR valve and any related sensors
- Repair, replace and reprogram PCM
This code only shows in vehicles equipped with step-down EGR valve systems.