Technical Description of OBD-II Trouble Code
The circuit for the Exhaust Gas Recirculation Temperature Sensor A is experiencing intermittent or erratic behavior.
What does that mean?
This is a generic diagnostic trouble code (DTC) that is commonly found in OBD-II vehicles, including Mazda, VW, Audi, Mercedes Benz, Ford, Dodge, Ram, and others.
While the code is generic, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
In the past, before the introduction of EGR (Exhaust Gas Recirculation) systems in the 1970s, engines would waste unburned fuel by expelling it into the atmosphere. Nowadays, vehicles must meet certain emission standards, which is where EGR systems come into play.
EGR systems help reduce emissions by recirculating fresh exhaust from the exhaust manifold and other parts of the exhaust system, allowing it to be re-burned and efficiently utilize the fuel.
The EGR temperature sensor is responsible for monitoring the temperature within the EGR system and adjusting flow using the EGR valve. It accomplishes this using a temperature-sensitive resistor-type sensor.
If your OBD scan tool displays the code P040E and associated codes, it means that the ECM has detected a fault within the EGR temperature sensor or its circuits. It’s important to note that the exhaust system is hot, so caution should be exercised when working in this area, even with the engine off.
The code P040E indicates an intermittent or erratic sensor reading within the EGR Temperature Sensor “A” circuit. Consult a vehicle-specific repair manual to determine which part of the circuit corresponds to “A” in your particular application.
What is the severity of this DTC?
The severity of this DTC can vary depending on the specific issue. However, it is not classified as severe since the entire EGR system was introduced as an emission reduction strategy. That being said, exhaust leaks and defective EGR temperature sensors are not beneficial for the vehicle, so timely maintenance is recommended.
Here is an example of an EGR temperature sensor:
What are some of the symptoms of the code?
Symptoms of a P040E trouble code may include:
What are some of the common causes of the code?
Causes for this P040E engine code may include:
What are some P040E troubleshooting steps?
Basic Step #1
First, visually inspect the sensor and the surrounding EGR system for any visible issues, paying particular attention to exhaust leaks. Also, examine the sensor and its harness. Keep in mind the high temperatures in this area, which can damage plastic and rubber insulated wires. Thoroughly inspect the wires for any signs of damage.
TIP: The presence of black soot may indicate an exhaust leak in the area.
Basic Step #2
Many EGR issues are caused by accumulated soot in the exhaust, which can result from poor maintenance or low-quality fuel. In this case, it may be beneficial to clean the EGR system or, at the very least, the temperature sensor. Note that sensors mounted within the exhaust system may feel seized when attempting to remove them.
Due to the substantial temperature fluctuations these sensors experience, applying a bit of heat using an Oxyacetylene torch (only for experienced individuals) may help loosen the sensor. Once the sensor is removed, soak it in carburetor cleaner or a similar product to effectively remove any accumulated soot. Use a wire brush to loosen soot in heavily accumulated areas. When reinstalling the clean sensor, apply some anti-seize to the threads to prevent seizing.
NOTE: Be cautious not to break the sensor inside the manifold/exhaust, as this can be an expensive mistake. Take care when loosening the sensor.
Basic Step #3
Verify the integrity of the sensor by measuring its actual electrical values compared to the manufacturer’s specified desired values. Use a multimeter and follow the manufacturer’s specific pin-out test procedures.
