TechASSIST Bulletin 02: EGT Sensors

What is an Exhaust Gas Temperature Sensor?

An EGT sensor is a thermistor encased in vibration-resistant cement and housed in a high-temperature stainless steel sheath. It’s designed to measure exhaust gas temperatures—often exceeding 900°C—and convert them into a voltage signal for the ECU.

The sensor's resistance changes with temperature. These changes are interpreted by the engine control unit (ECU) to help regulate various emissions systems and engine functions.

A labeled diagram of a sensor component showing parts from left to right: NUT, THREAD, STAINLESS STEEL WIRE, PT WIRE, THERMISTOR, CEMENT, and SENSOR NOSE/TIP.

What Does an EGT Sensor Do?

EGT sensors serve multiple purposes in both petrol and diesel vehicles. Their core functions include:

Protecting components such as the DPF, turbocharger, and catalytic converter from overheating
Supporting emissions control systems like Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR)
Assisting DPF regeneration by monitoring temperature thresholds
Controlling turbo boost pressure in real-time

The sensor's specific function depends on its location within the exhaust system.

A schematic diagram of an engine system showing labeled components including the engine, turbo, DPF, catalytic converter, and multiple EGTS sensors positioned before and after key parts.

Typical EGT Sensor Locations

Sensor positions vary by vehicle, but common locations include:

Before and after the turbocharger – To monitor boost temperature. Pre-turbo sensors endure the highest temperatures (up to 900°C), while post-turbo gases cool to around 400–500°C.
Before and after the DPF – To support regeneration cycles by confirming the correct temperatures for soot combustion (200–400°C).
Before and after the catalytic converter – To prevent overheating and monitor the SCR process. Gases here are typically around 100–200°C.

Most modern vehicles now feature at least four EGT sensors, especially diesels with advanced emissions systems.

Common Causes of EGT Sensor Failure?

Extreme Heat

Continuous exposure to temperatures nearing 900°C naturally causes wear over time.

Damaged or Broken Wires

EGT sensors can be damaged during unrelated repairs, especially if nearby components like the DPF or exhaust are replaced. Twisted or kinked wires are a frequent issue.

Vibration

While sensors are designed to resist vibration, the constant stress of engine operation can still lead to sensor fatigue or internal fractures over the long term.

Tip: When replacing major exhaust components, it’s good practice to replace the EGT sensors at the same time to avoid future failures and ensure system compatibility.

A person in blue overalls holding a hose connected to a vehicle’s exhaust pipe, with glowing rings and digital icons surrounding the hose area, suggesting analysis or measurement.

Symptoms of a Faulty EGT Sensor

Reduced fuel efficiency:

Faulty readings can prolong DPF regeneration or trigger unnecessary cycles, leading to excess fuel usage.

Drivability issues:

Hesitation, power loss, or irregular DPF regeneration events may occur.

Illuminated check engine light:

NTC

NTC (Negative Temperature Coefficient) sensors often trigger an immediate fault code.

PTC

PTC (Positive Temperature Coefficient) sensors can fail more subtly, continuing to send misleading signals that interfere with DPF or SCR function, making diagnosis trickier.

The rear end of a car with visible emissions coming from the exhaust pipe, featuring a red reflective strip and a triangular reflector on the bumper.

EGT Sensor Fitting Tips

Always allow the exhaust system to cool fully before starting work.
Handle sensors with care – dropping them can damage the internal thermistor or its cement fixing.
Clean the exhaust thread using a suitable cleaning tap before installing threaded sensors.
Apply copper grease to the thread only – never grease the sensor tip or nose. This helps prevent thread galling and eases removal later.
Torque to spec – Use an open-ended torque wrench and follow manufacturer guidelines to avoid overtightening or damaging the wires.
Check system function after installation – Start the engine and ensure proper operation. A fault code reset or ECU adaptation may be necessary.

As vehicles become more emissions-focused, components like EGT sensors are now mission-critical. By understanding their role and following correct diagnostic and installation procedures, independent workshops and factors can confidently meet growing demand and avoid costly comebacks.

For quality aftermarket replacements, ensure you're fitting OE-matching parts supported by robust warranty and technical support.

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