EXHAUST GAS TEMPERATURE SENSORS
The Premier Auto Trade Emission range includes more than 110 Exhaust Gas Temperature Sensors
The purpose of the exhaust-gas temperature (EGT) sensor is to monitor the exhaust-gas temperature at various locations in the exhaust system, something it does using an electrical voltage signal.
The number of EGT sensors in a vehicle will vary depending on the systems used. They are used in both diesel and petrol engines, naturally aspirated and turbocharged, as described below.
The function varies slightly for Diesel engines. The temperature of the DPF (Diesel Particulate Filter) is monitored, not so much for heat overload but to establish that the temperature required for regeneration (self-cleaning) of the DPF has been achieved.
Also used for control and protection from overheating of SCR (selective catalyst reduction) or LNT (lean NOx trap) and other NOx Absorbers.
Certain EGR systems are now equipped with temperature sensors for EGR Diagnosis (OBD) which are Compact and have lower Maximum temperature measurement. (400Deg C).
Used primarily to protect the turbo charger and catalytic converter from thermal overload (overheating), the PCM will alter timing, fuel mixtures and boost pressure to lower the temperatures (results in loss of power). Also used for control and protection from overheating of NOx reduction systems.
Typical EGT sensor locations
The diagram shows typical locations in a VW Jetta, Golf and Audi A3. Other models may have many more sensors downstream for more monitoring.
Identifying the EGT sensor that requires testing and/or replacing can be a little confusing when the vehicle Is fitted with multiple units. The OBD 11 diagnostic system uses a listing similar to the O2 sensor identification.
Effects on vehicle when sensor fails
Over time a sensor can drift out of tolerance limits causing over fuelling issues during Regeneration, due to the process being prolonged.
Both Positive (PIC) and negative (NTC) temperature coefficient sensors are used to monitor the exhaust temperature.
PTC sensors may continue to relay misinformation to the ECU without setting or delaying a diagnostic trouble code. This may cause the DPF to regenerate outside of its permitted temperature range.
In many cases, a DPF has been incorrectly diagnosed as a fault where it has been caused by a faulty EGT sensor.
NTC sensors are generally designed with two wires bonded to a ceramic cell. Over time, an open circuit may be created and resulting in a fault code being logged. This is generally a straight forward fix and repair.
Other causes of failure and test procedure
Another cause of sensor failure can be physical damage. These sensors may be damaged during exhaust replacement procedures and its recommended they are to be replaced simultaneously with any DPF or other major exhaust component fitted with an EGT sensor.
Bending the sensor wires excessively can also cause failure. In this case the sensor is to be refitted at the correct angle to prevent stretching and over bending.
Severe vibration may also cause internal component or wire connection damage, as may excessive prolonged temperature (over 900 Deg) which may cause Thermistor element failure. Contamination from oil, antifreeze and poor-quality fuel can also cause sensor failure.
The Premier Auto Trade Emission range
The Premier Auto Trade Emission range includes more than 110 Exhaust Gas Temperature Sensors (EGT), covering over one million vehicle applications in Australia and NZ.
For more information visit www.premierautotrade.com.au