Part Focus: Exhaust Gas Sensors / Brands: Volt
In this bulletin we’ll take a look at the Exhaust Gas Temperature Sensor’s role, how they work and offer diagnostic and fitting advice for successful replacement.
Exhaust Gas Temperature (EGT) Sensors are now used on over 30% of all new vehicles including most major manufacturers such as Volkswagen Automotive Group, Ford, Fiat, BMW, Renault and Mercedes to name just a few. Although a relatively recent introduction, the aftermarket is seeing an increasing demand for replacements.
What is an Exhaust Gas Temperature Sensor?
The Exhaust Gas Temperature sensor is simply a thermistor element fixed in cement to protect from vibration and housed in stainless steel to withstand extreme temperatures of up to 900°C. Changes in temperature result in changes in resistance of the sensor and this is communicated to the ECU as a voltage.
What does the Exhaust Gas Temperature Sensor do?
Exhaust Gas Temperature sensors protect vital exhaust components from overheating and help to control emissions. They are also used in several combustion control processes in both diesel and petrol engines including Selective Catalytic Reduction (SCR), Turbo Boost, Exhaust Gas Recirculation and Diesel Particulate Filter (DPF) Regeneration. The specific role of each sensor depends upon its location in the exhaust system.
Exhaust Gas Temperature Sensor Locations
The location of Exhaust Gas Temperature sensors varies from vehicle to vehicle depending on the layout of the exhaust system. The diagram below shows typical locations:
Before and after the turbo to monitor turbo boost conditions. Sensors before the turbo are subjected to the most extreme temperatures of up to 900°C. Passing through the turbo cools gases to around 400-500°C. Before and/or after the DPF to assist in DPF regeneration process, which uses extreme temperatures to burn off excess particulate matter (soot.) At this point gases are around 200-400°C.
Before and/or after the catalytic converter to protect from over heating and to monitor the selective catalytic reduction process. Usually gases by this point are around 100-200°C. Most modern vehicles will feature at least four Exhaust Gas Temperature sensors.
Causes of Failure
Extreme Heat: As discussed, the Exhaust Gas Temperature sensor can be subjected to intense heat of up to 900°C so it’s no surprise that they may start to suffer over time.
Broken Wires: A common problem with all wired sensors is that wires can break, especially if subjected to harsh twists and turns. They are also easily damaged when replacing other components in the exhaust system. As a result Volt recommend that exhaust sensors are replaced at the same time as the exhaust system or components such as the DPF or CAT. This will ensure protection of the new (often expensive) components.
Vibration: Exhaust Gas Temperature sensors have many features to help them withstand vibration but it can still take its toll over time.
Symptoms of Failure:
Decrease in Fuel Efficiency: A faulty sensor communicating incorrect voltages can result in over fueling due to DPF regeneration taking longer to complete
Drivability Issues: The DPF regeneration process can affect drivability. Faulty Exhaust Gas Temperature sensors can lead to unnecessary regenerations causing inconvenience for the driver.
Engine Check Light: Some sensor types are harder to diagnose than others. PTC type sensor failures are often misdiagnosed as DPF issues as after failure they continue to function sending incorrect signals to the ECU affecting the DPF regeneration process. NTC type sensors are more likely to trigger the engine check light on failure.
Exhaust Gas Temperature Sensor Installation Advice:
Ensure the exhaust system is cool before starting work.
Handle the Exhaust Gas Temperature sensor carefully, dropping the component may cause unseen damage to the cement that secures the thermistor.
If the sensor is threaded, clean the thread in the exhaust pipe with a cleaning tap.
Apply copper grease on the sensor thread only. DO NOT GREASE THE SENSOR NOSE. Although some sensors are pre-greased, the extra grease will prevent thread galling and reduce friction which could lead to over torque.
Tighten the sensor to the required torque as prescribed by the vehicle manufacturer, using an open-ended torque wrench to avoid over-tightening and/or damage to the wire.
Turn the engine on and check if the exhaust system works properly. A reset of the ECU may be required.
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