Exhaust gas temperature (EGT) sensors let the ECM monitor exhaust heat, protect the turbo and DPF, and manage regeneration. Modern emissions diesels use several EGT sensors along the exhaust. A failed sensor can cause regen problems, limp mode, incorrect fan operation, or false over-temperature warnings. Testing an EGT sensor is mostly a resistance and live-data check. Here is how to do it.
How EGT sensors work
Most are thermistors or thermocouples whose resistance or voltage changes with temperature. The ECM compares several sensors to manage regen and protect components. A sensor reading far off from its neighbors, or stuck, sets a code and can disrupt the regen strategy or throw the truck into a derate.
Step-by-step test
- With a scan tool, read all EGT sensors with the engine cold. They should all read close to ambient temperature and to each other.
- Start the engine and watch the values rise together as the exhaust heats. A sensor that stays flat, reads wildly high, or lags the others is suspect.
- With the engine off and cool, unplug the suspect sensor and measure its resistance with a multimeter; compare to the specification and to a known-good sensor of the same type.
- Inspect the connector and harness for heat damage, corrosion, and chafing, common near the hot exhaust.
- Confirm the sensor's reference and ground circuits are intact per service data.
- Clear codes after any repair and verify all sensors track together during warm-up and a short drive.
Reading the results
Healthy EGT sensors all read ambient when cold and climb together when running. An outlier that is stuck, far off, or reads open is the failed unit, provided its wiring and connector are good. Because these sensors live in extreme heat, damaged connectors and chafed harnesses are common and mimic a bad sensor, so always inspect the wiring.
Why an accurate EGT reading matters
EGT is not just a gauge value; the ECM uses it to protect expensive hardware and to run regeneration correctly. A faulty sensor can have real consequences:
- Regens that will not initiate or complete, leading to a loaded DPF.
- Unnecessary derates or limp mode when the ECM sees a false over-temperature.
- Incorrect cooling fan behavior tied to exhaust temperature strategy.
- Masking of a genuine over-temperature condition that could damage the turbo or DPF.
Because of that, do not simply clear the code and drive. Confirm which sensor is at fault, repair the wiring or replace the sensor, and verify all of them track together before trusting the regen system again.
Frequently asked questions
How many EGT sensors does a diesel have?
Modern emissions diesels typically use several along the exhaust to manage the turbo, DPF, and regeneration. The exact number varies by engine.
What are the symptoms of a bad EGT sensor?
Regen problems, limp mode or derate, incorrect fan operation, and false temperature warnings. A code usually names the affected sensor location.
Can I just clear the code?
No. A faulty EGT sensor disrupts regen and protection strategies, so confirm and repair it. For sensors and connectors, email sales@coredieselparts.com.
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