EGT Sensors

When most people think about diesel emissions on modern diesel engines, they think about diesel particulate filters, diesel oxidation catalysts, or the selective catalytic reduction. All of these components play an important part and offer significant features in helping an engine run efficiently while keeping pollutants to a minimum. But sensors play a significant role in how effective the entire vehicle operates, and the exhaust gas temperature sensor can lead to many problems if not maintained correctly.

In fact, the exhaust gas temperature (EGT) pyrometer is one of the most important gauges on a modern diesel engine. It can warn the vehicle operator that something is wrong with an appropriate response before damage is done to the engine, and it can be used to achieve better fuel economy. 

The exhaust gas temperature sensor measures just what you think it would: the exhaust gas temperature. Similar to the functions of a thermocouple, it sends voltage signals to the truck’s Engine Control Module (ECM) or Electronic Engine Control Unit (ECU). The engine then uses the data to adjust its timing for optimum performance by reducing fuel input into the combustion chamber during high load periods or slowing timing at low loads. By doing so, the exhaust gas temperature sensor and the ECU work together to ensure the truck is neither overheating nor underperforming, but rather staying within an optimal range.

Diesel engines operate between 190 – 220 degrees. This means that diesel exhaust sensors are constantly hot to the touch, even when they are working properly. This high-heat environment can cause damage to the internal engine and exhaust if it is not regulated.

The diesel exhaust temperature sensors are usually screwed into bungs on the body of the diesel particulate filters, diesel oxidation catalysts, or the selective catalytic reduction. In modern systems, there is an average of three in the emissions system alone. This is to ensure the temperature is stable at multiple points throughout. The locations of these sensors will vary depending on the Year, Make, Model, and Engine of your truck. Consult your owner’s manual or trusted technician for information on your specific truck.

The sensing component interacts with the temperature of the gas passing by it, creating electrical resistance. In negative temperature coefficient (NTC) sensors, resistance decreases as the temperature increases. In positive temperature coefficient (PTC) sensors, resistance increases as temperature increases. Your vehicle may utilize one or both types.

Diesel sensors measure the exhaust gas temperature, then calculate an average of that measurement over time. It then sends a signal to the ECM or ECU, which adjusts its timing to achieve optimum performance. However, if the temperature is drastically increased or the component is malfunctioning, there are a few ways you might find out.

The most common way a vehicle operator is alerted to an exhaust gas temperature sensor failing is when the ECM or ECU triggers a dashboard warning light. The operator may have noticed reduced fuel efficiency leading up to the failing of this mechanism. Another symptom of the exhaust gas temperature sensor failing is unnecessary DPF regens. This is due to the ECU operating as if the engine is under heavy stress.

The after-treatment mechanisms operate best when high heat causes passive regeneration, but this is a delicate balance because excessive heat caused by a faulty exhaust gas temperature sensor can lead to the failure of other after-treatment components. If you find that you are replacing other after-treatment parts prematurely, the root cause could be a faulty exhaust gas temperature sensor.

The diesel engine’s EGT sensor is designed to operate at extreme temperatures and therefore has a short lifespan compared to other parts. The exhaust gas temperature sensor can fail for various reasons, including corrosion, overheating, or dirt buildup on the probe element. The connections or wires may have also come loose during operation due to vibrations. Also, if you have had a leak recently, your wiring may have been contaminated with fluids like antifreeze or oil. Finally, the sensor or connections may have been knocked loose during a recent unrelated repair.

As diesel engines run hotter, their efficiency decreases because more fuel is needed to produce power. High EGT readings can be caused by a number of problems, including over-fueling, overheating, or blocked air intake filters or ducting. Plugged exhausts can also lead to an exhaust gas temperature sensor failing prematurely.

Driver habits play a role in this as well. If a driver is towing a heavy load uphill and then accelerates too fast downhill, this can lead to problems with the mechanism. If the driver is over revving the vehicle, failing to shift at the correct time, and abusing the truck, this can also lead to issues. Drivers should take care to run the engine according to best practices, as this will extend the wear rate and lifespan of the internal components.

We should also mention the importance of regular after-treatment maintenance. While the after-treatment system, including DOCs, DPFs, and sensors, is designed to run in the background, the whole structure will be more efficient if it is properly cared for. Honoring the appropriate service intervals will help identify unusual wear before it turns into a catastrophic failure. Understanding these inner workings will also help you identify potential issues and avoid unplanned downtime. Here’s everything you need to know about after-treatment maintenance.

The first step is to use a diagnostic tool to read the fault codes. Repair technicians will use their diesel laptops for this, but vehicle operators can use a tool like Diesel Decoder.

If there are no fault codes, but you still suspect that there is a problem, the next thing you should check is the wiring and connections. When checking the wiring and connections, you may see that there is a buildup of soot or dirt, which can interfere with readings. Use a dry cloth to wipe the sensor clean. Recheck the connections and then test the sensor. Testing the sensor involves using a voltage meter and checking the sensor before and during running the engine. Typically, you want to see 5 volts, but when the engine is off, some repair technicians have seen that go up to battery voltage. Repeat these steps for all EGT components.

Once you have located the faulty sensor, it is important to note the position of the sensor since there can be three or more sensors in the typical diesel vehicle. The sensor could be upstream or downstream of the turbocharger or diesel particulate filter or within the NOx reduction system.

When you disconnect the electrical connector, take a look at the wiring to make sure that everything is in good shape. Next, you will unscrew the sensor using a socket wrench and remove it. Be careful not to damage any nearby components. Follow the manufacturer’s directions to install the replacement. Remember that these mechanisms are one of the more delicate parts of your after-treatment system, so utilize care when installing. Also, be aware that twists or kinks in the wiring may cause the connections to break over time.

At DPFPartsDirect.com, we offer high-quality after-treatment parts. We aren’t just a place to buy parts directly. We also have knowledgeable customer service experts to help you get the right part the first time. We have EGT sensors for many of the popular heavy- to light-duty trucks on the market. 99% of our products are eligible for same-day shipping since we want to get your vehicles back on the road.