How serious is this DTC?
The severity here varies considerably depending on your specific issue, but I wouldn’t classify it as serious given that the entire system was introduced in vehicles simply as an emissions reduction strategy. That being said, exhaust leaks are not “good” for your vehicle, nor are leaking or faulty EGR temperature sensors, so maintenance is key here, sooner or later!
An example of an EGR temperature sensor:
What are some of the symptoms of the code?
Symptoms of a P040D fault code may include:
- Failure of state/provincial smog or emissions test
- Engine noise (knocking, rattling, ticking, etc.)
- Louder exhaust
- Excessive exhaust odors
What are some common causes of the code?
Causes of this P040D engine code may include:
- Faulty or damaged EGR (Exhaust Gas Recirculation) temperature sensor
- Leak from the EGR temperature sensor gasket
- Cracked or leaking exhaust pipe where the sensor is mounted
- Burned wiring harness and/or sensor
- Damaged wire(s) (open, short to power, short to ground, etc.)
- Damaged connector
- ECM (Engine Control Module) issue
- Poor connections
What are the troubleshooting steps for P040D?
Note: For reference, this code is more commonly found on Ford Powerstroke and Dodge/Ram Cummins vehicles.
Basic Step #1
The first thing I would do here is check everything we can see by simply inspecting the sensor and the surrounding EGR system, looking for exhaust leaks in particular. Also check the sensor and its harness while you’re at it. Remember what I said about those high temperatures? They can wreak havoc on plastic and rubber insulated wires, so inspect them carefully.
TIP: Black soot can indicate an exhaust leak around the area.
Basic Step #2
Many EGR issues I’ve seen in the past have been caused by soot buildup in the exhaust, potentially caused by a number of things (poor maintenance, low-quality fuel, etc.). In this case, it’s no exception, so it may be wise to clean your EGR system or at the very least the temperature sensor. Be aware that sensors mounted in exhaust systems can feel seized when you attempt to remove them.
Remember that these sensors are subjected to significant temperature fluctuations, so a bit of heat using an oxyacetylene torch (not for the novice) can help loosen the sensor. Once the sensor is removed, use carburetor cleaner or a similar product to effectively soak the soot. Use a wire brush to dislodge soot in heavily built-up areas. When reinstalling the cleaned sensor, be sure to apply some anti-seize compound to the threads to help prevent seizing.
NOTE: The last thing you want to do here is break the sensor inside the manifold/exhaust. This could be a costly mistake, so be patient when loosening the sensor.
Basic Step #3
Check the sensor’s integrity by measuring the actual electrical values against the manufacturer-specific desired values. To do this, use your multimeter and follow the manufacturer-specific pinout test.