Check the exhaust temperature sensor

Take VW Passat 2.0 16 V TDI as an example. It introduces the useful knowledge and valuable skills of testing the exhaust gas temperature sensor
In modern models, the exhaust temperature sensor is installed in different positions in the exhaust system of diesel and gasoline vehicles. The exhaust gas temperature sensor detection, such as a catalytic converter or the temperature in front of the diesel formation filter, and send it as a voltage signal to the engine control unit. The engine control unit needs to control this information to control the regeneration of the air -fuel ratio or particle filter, thereby effectively reducing emissions. In addition, high -temperature sensors can protect components in the thermal exhaust air area from severe overheating.

1. exhaust gas temperature sensor: design and function
The measurement end of the exhaust gas temperature sensor is installed with a resistor, which changes with the temperature. These resistors are called heat -sensitive resistors and are divided into two groups. Here is a distinction between NTC thermistor and PTC thermistor, depending on their temperature characteristics (Figure 1).

NTC — negative temperature coefficient resistance (the resistance decreases with the increase in temperature)

PTC — Positive temperature coefficient resistance (the resistance increases with the temperature increases)

The exhaust temperature sensor (EGTS) is usually directly connected to the engine control unit (ECU). The sensor and another resistor (RUP) in the control unit form a series connection to allocate the voltage through the connection. The signal was measured on the sterilizer and converted to temperature information through the algorithm (Figure 2).

2. exhaust gas temperature sensor -symptoms: effect
If the exhaust gas temperature sensor fails, the following impact may occur:
The electric congestion system warning light flickering
Grying filter warning lights are on
The engine control light light
Increased exhaust gas emissions (CO, NOX and HC)
Due to the shortened interval of the particle filter, the driving performance is not good
The regeneration time of a longer particle filter leads to an increase in fuel consumption
Performance loss caused by error detection of particle filter saturation

3. Failure of exhaust gas temperature sensor: cause of failure
The following reasons may be the cause of the failure of the exhaust temperature sensor:
electricity failure
External damage
The strong vibration of the exhaust system causes internal damage to the wire
Due to the defects in the jet system or air fuel mixture, the temperature of the exhaust gas is too high

4. Check the exhaust temperature sensor: failure elimination
System overall

The following information takes the 2015 Volkswagen Passat 2.0 16 V TDI as an example. According to the characteristics of the vehicle, up to four exhaust gas temperature sensors can be installed. The engine controls the temperature of the catalytic converter, the turbocharger, and the temperature of the upstream and downstream of the diesel particles filter.
In vehicles without SCR (selective catalytic restoration) catalytic converters, the exhaust gas temperature sensor behind the diesel particles filter is not required. If the exhaust gas temperature sensor fails or the output value is not credible, the system will switch to the emergency operating mode or use the alternative value to protect the relevant components from overheating. Then record an error entry in the engine control unit, and the warning light in the dashboard is activated.

Use the diagnostic unit for exhaust temperature sensor test

The function of the exhaust temperature sensor is monitored by the corresponding superior system control unit. Any errors that appear are stored in the error deposit of the control unit, and the appropriate diagnostic unit can be replaced. According to the system, additional parameters can be displayed and used for failure.

1. Error code

In this function, you can read and delete an error code stored in an error deposit. In addition, you can call information about error code.

In our case studies, the error code 15709 and 5257 showed the failure of the exhaust temperature sensor 3.

2. Parameters
In this function, the current measurement value of the sensor in the control unit can be displayed and evaluated.
The illustration shows a vehicle with three exhaust gas temperature sensors
Sensor 3 shows a negative 40 degree value, which may be due to the disruption of the wire or the sensor's defect.

3. Circuit diagram
The system -specific circuit diagram can be obtained from the vehicle information and used for fault exclusion. You can read the PIN allocation or cable color on the exhaust gas temperature sensor and use it for further testing.

Maintenance and maintenance instructions
As part of the failure of failure, the components and peripheral equipment in the engine cabin should be first inspected after the ECU diagnosis.
If the cable or sensor shell is damaged, the sensor should be replaced.
If the thread of the exhaust gas temperature sensor is coated, it is not allowed to use additional hotline cream.
The exhaust gas temperature sensor must be tightened according to the prescribed torque! We recommend using 40-45 nm tight torque to Hella exhaust temperature sensor.
Please also follow the corresponding maintenance and maintenance instructions provided by various automobile manufacturers!