Technical Description of OBD-II Trouble Code
The circuit for the Exhaust Gas Recirculation Temperature Sensor A is registering a high value.
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 exact repair steps may vary depending on the year, make, model, and powertrain configuration, this code indicates a fault in the EGR (Exhaust Gas Recirculation) temperature sensor or its circuits.
In the past, engines used to waste unburned fuel by expelling it into the atmosphere. However, modern vehicles are required to meet certain emission standards. The introduction of EGR systems has significantly improved emissions by recirculating and re-burning fresh exhaust, ensuring efficient fuel combustion.
The EGR temperature sensor plays a crucial role in this system by allowing the ECM (Engine Control Module) to monitor the temperature within the EGR system and adjust flow through the EGR valve. It uses a temperature-sensitive resistor-type sensor to accomplish this.
If your OBD scan tool displays the code P040D and associated codes, it means that the ECM has detected a high electrical value in the EGR Temperature Sensor “A” circuit. Consult a vehicle-specific repair manual to identify the “A” part of the circuit for your particular application.
What is the severity of this DTC?
The severity of this DTC depends on the specific issue you are facing. However, it is not classified as severe since the EGR system was primarily introduced as an emission reduction strategy. Nevertheless, exhaust leaks and defective EGR temperature sensors are not beneficial for your vehicle, so it is important to address the issue promptly.
Here is an example of an EGR temperature sensor:
What are some of the symptoms of the code?
Symptoms of a P040D trouble code may include:
What are some of the common causes of the code?
Causes for this P040D engine code may include:
What are some P040D troubleshooting steps?
Note: Anecdotally, this code is more commonly found on Ford Powerstroke and Dodge/Ram Cummins vehicles.
Basic Step #1
Start by visually inspecting the sensor and the surrounding EGR system. Look for exhaust leaks, especially around the sensor. Also, examine the sensor and its harness. Keep in mind the high temperatures involved, 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 your EGR system or, at the very least, the temperature sensor. Be cautious when dealing with sensors mounted within the exhaust system, as they may feel seized. Applying a bit of heat using an Oxyacetylene torch (only for experienced individuals) can help loosen the sensor. Once the sensor is removed, soak it in carburetor cleaner or a similar product to remove soot. Use a wire brush to loosen any excessive accumulation of soot. When reinstalling the clean sensor, apply some anti-seize to the threads to prevent seizing.
NOTE: Be careful not to break the sensor inside the manifold/exhaust, as this can be an expensive mistake.
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.
