What is an exhaust gas temperature sensor?

What is an exhaust gas temperature sensor?

As its name suggests, the exhaust gas temperature sensor measures the temperature of the exhaust gas. This information is then relayed back to the engine control unit or ECU, where appropriate action is taken. In petrol engines, its main role is to protect key components from the higher temperatures common with downsized engines – so if the sensor detects excessive temperatures, the ECU will reduce the temperature, by lowering boost pressure in the case of the turbocharger, for example, or increasing the quantity of fuel injected for the catalytic converter. In diesel engines, exhaust gas temperature sensors are also used to monitor the temperature of the diesel particulate filter (DPF) to establish the correct temperature for regeneration, reducing harmful emissions. It is not uncommon to have three or more sensors fitted to the exhaust; one prior to the turbocharger, one before the DPF and the third after the particulate filter.
How do exhaust gas temperature sensors work?

There are two types of exhaust gas temperature sensors; one with a positive temperature coefficient (PTC) sensing element, and the other a negative temperature coefficient (NTC), the only difference being how they measure the temperature. The NTC element has a high resistance at low temperatures and a low resistance at high temperatures. In other words, its resistance decreases as the temperature increases. Whereas in a PTC element, the most common type, resistance increases in line with temperature. Either way a temperature is assigned to the resistance in the ECU and action taken accordingly.
Why do exhaust gas temperature sensors fail?

One of the common causes of exhaust gas temperature sensor failure is exposure to excessively high temperatures – over 900°C in some case - the very thing they protect other components from. Like all wired sensors, severe vibration can also loosen internal connections and any bends or twists can cause the wire to break, making them particularly vulnerable to damage when replacing other components in the exhaust system. These, alongside contamination from other fluids such as oil or antifreeze, can all affect the sensor’s response characteristics, causing it to drift out of tolerance and provide inaccurate readings.
What are the symptoms of a faulty exhaust gas temperature sensor?

A faulty exhaust gas temperature sensor can negatively affect a vehicle’s after-treatment system, resulting in the following symptoms:

-Check engine light: if the ECU detects a problem with the sensor or signal, it will trigger the check engine light to come on.
-Reduced fuel efficiency: if the sensor relays incorrect voltages, the DPF regeneration process can take longer, resulting in increased fuel usage.
-Unnecessary DPF regeneration: faulty sensors can also lead to unnecessary regenerations, causing inconvenience to the vehicle owner.
-Failed emissions test: a false reading can cause the EGR system to malfunction, without triggering the check engine light. This can result in an emissions test fail.
-Component failure: increases in exhaust temperatures can also contribute to the premature failure of other exhaust or internal engine components.
What are common exhaust gas temperature sensor fault codes?
Common fault codes include:

-P0544: Exhaust gas temperature sensor, bank 1, sensor 1 - circuit malfunction
-P0546: Exhaust gas temperature sensor, bank 1, sensor 1 - high input
-P2033: Exhaust gas temperature bank 1, sensor 2 - circuit high
-P247A: Exhaust gas temperature sensor bank 1, sensor 3 – out of range
-P0549: Exhaust gas temperature sensor, bank 2, sensor 1 - circuit high
-P2031: Exhaust gas temperature bank 1, sensor 2 - circuit malfunction
for more information:
https://www.delphiautoparts.com/gbr/e...
https://www.denso-am.eu/products/auto...
https://www.hella.com/techworld/us/Te...