Technical Description of OBD-II Trouble Code
The circuit for the Exhaust Gas Recirculation Temperature Sensor A is experiencing low voltage.
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, etc.
While the code is generic, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
Prior to the introduction of Exhaust Gas Recirculation (EGR) systems in the 1970s, engines would release unburned fuel into the atmosphere. Nowadays, vehicles must meet certain emission standards in order to be produced.
EGR systems have significantly improved emissions by recirculating fresh exhaust back into the engine to ensure efficient fuel combustion. The EGR temperature sensor plays a crucial role in this system by monitoring the temperature and adjusting flow through the EGR valve using a temperature-sensitive resistor-type sensor.
If your OBD scan tool displays the code P040C and related codes, it means that the ECM has detected a fault in the EGR temperature sensor or its circuits. It is important to note that the exhaust system is hot, so caution should be exercised when working in this area.
The code P040C is set when the ECM detects a low electrical value in 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 varies depending on the specific issue. However, it is not classified as severe since the EGR system was primarily introduced as an emission reduction strategy. Nonetheless, 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 P040C trouble code may include:
What are some of the common causes of the code?
Causes for this P040C engine code may include:
What are some P040C 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 be difficult to remove due to seizing. Applying some 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 heavily accumulated soot. When reinstalling the clean sensor, apply 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.
Basic Step #3
Verify the integrity of the sensor by measuring its actual electrical values compared to the manufacturer’s specified values. Use a multimeter and follow the manufacturer’s specific pin-out test procedures.
