Exhaust gas temperature sensor - EGT

Exhaust gas temperature sensor - EGT

 

 

What is an exhaust gas temperature sensor?

 

As the name suggests, exhaust gas temperature sensor measures the exhaust gas temperature. This information is then passed 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 in 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, or by increasing the amount 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 to set the correct temperature for regeneration, reducing harmful emissions. It is not uncommon to have three or more sensors mounted on the exhaust;

 

How do exhaust gas temperature sensors work?

There are two types of exhaust gas temperature sensors; one with a positive temperature coefficient (PTC) and the other with a negative temperature coefficient (NTC), the only difference being how they measure 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, resistance increases with temperature. In any case, a temperature is assigned to the resistance in the ECU and acted upon 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 cases. Like all hard-wired sensors, severe vibration can weaken the internal connections and any bending or twisting can cause the wire to break, making them particularly vulnerable to damage. This, along with contamination from other fluids such as oil or antifreeze, can affect all of the sensor's response characteristics, causing it to go out of tolerance and give inaccurate readings.

What are the symptoms of a faulty exhaust gas temperature sensor?

 

A faulty exhaust gas temperature sensor can adversely affect a vehicle's aftertreatment system, resulting in the following symptoms:

• Engine check light - if the ECU detects a problem with the sensor or signal, the check engine light will come on.
• Low fuel efficiency - if the sensor transmits incorrect voltages, the DPF regeneration process may take longer, leading to increased fuel consumption.
• Unnecessary DPF regeneration - Faulty sensors can also lead to unnecessary regenerations, causing inconvenience.
• Emissions testing failed - a false reading can cause the EGR system to malfunction without triggering the check engine light. This can lead to emissions test failure.
• Component failure - Increased exhaust temperature can also contribute to premature failure of other exhaust or internal engine components.

How to diagnose an exhaust gas temperature sensor?

 

To diagnose a faulty exhaust gas temperature sensor, consider the following steps:

• Perform a scan and read error codes using a diagnostic tool.
• Inspect connectors for signs of corrosion or loose connections.
• Check the wiring for any breaks or damage that could cause a short circuit.
• Inspect the sensor for any build-up of contaminants and clean with a clean, dry cloth as necessary.
• To test the sensor, use a separate IR meter and compare the readings with the live data obtained when using a diagnostic tool. Start the engine so that the exhaust rises in temperature and compare the readings.
• With the ignition on and the EGT sensor plug disconnected, measure the voltage at the sensor connector - there should be 5 volts. If not, then trace the wire back to the ECU and check the power there.