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How to check the exhaust gas temperature sensor

11.10.2022

How to check the exhaust gas temperature sensor

Although hidden from view, Exhaust Gas Temperature Sensors (EGT Exhaust Temperature Sensor) play an important role in modern engines. In an era of high emissions requirements, measuring temperatures in the exhaust system helps ensure optimal engine operating conditions and protect components such as the turbocharger, catalytic converter and particulate filter from overheating.

Where are exhaust gas temperature sensors used?

The sensors are used in both gasoline and diesel engines. On gasoline units without a GPF particulate filter, the EGT sensor primarily protects individual system components from excessive temperatures. In this case, the sensor is usually placed through the oxidation catalyst. Based on the sensor readings, an algorithm in the engine controller adjusts fuel dosage and boost pressure so that temperatures are within a safe range. Diesel engines equipped with exhaust aftertreatment systems tend to use more sensors in different positions. For example, in the 2015 Passat 2.0 16 V TDI, you’ll even find four exhaust gas temperature sensors:

  • Before the turbocharger;

  • Before DOC oxidation catalyst;

  • Before the DPF;

  • Behind the DPF.

More sensors allow more precise control of the drive unit, minimizing exhaust emissions. Key to reducing exhaust emissions is the filter regeneration process. If the temperature is too low, the filter will not be able to clean itself properly, while too high a temperature can, in turn, damage the filter. The ECU control unit uses an EGT sensor to monitor the self-cleaning process.

The figure below (compiled from materials from one of the sensor manufacturers) shows the possible placement points (10 in total) and required sensor temperature ranges for an advanced compression-ignition unit. Usually there are fewer sensors, but there is a tendency to increase their number.

The exhaust gas temperature sensor affects the exhaust gas aftertreatment system. Failure of the exhaust gas temperature sensor means more exhaust emissions.

OPERATION OF EXHAUST GAS TEMPERATURE SENSORS

Two basic types of exhaust gas temperature sensors are used:

  • NTC type sensors. They are thermistors that have a negative temperature coefficient. This means that the resistance decreases with increasing temperature, and the characteristic is strongly nonlinear. In this respect, they work similar to coolant temperature sensors. Depending on the range of permissible temperatures, different characteristics are used.

  • PTC sensors are usually platinum thermoresistive sensors with a positive temperature coefficient. This means that the resistance increases as the temperature increases. The characteristics of sensors of this type are much more linear, and the typical characteristic resistance is 200Ω at 0॰C.

SYMPTOMS OF AN EMERGENCY

Although exhaust gas temperature sensors are designed to operate under these conditions, they are quite vulnerable components. Extreme conditions in the exhaust system (temperature changes, strong vibrations, contamination) can damage the sensor after a while. Improper operation of components such as injectors can shorten the life of the sensor. Symptoms of a faulty sensor may include:

  • Glowing on the engine light or the particulate filter light on the dashboard.

  • Increased fuel consumption.

  • Performance reduction related to improper assessment of the amount of soot in the DPF filter.

  • Premature failure of system components – such as the DPF or turbocharger.

  • Improper composition of exhaust gases which may result in a problem during the technical examination.

Increased emissions, excessive fuel consumption or other manifestations of improper engine operation can be the result of a defective exhaust gas temperature sensor.

HOW TO TEST THE EXHAUST GAS TEMPERATURE SENSOR?

There are two main ways to check sensors – with on-board diagnostics and independently.

ON-BOARD DIAGNOSTICS

To determine what the exhaust gas temperature is, the engine controller measures the resistance of the sensor. Classically, a voltage divider is used, consisting of a resistor in the controller and the sensor in question (usually supplied with 5V). The controller measures the voltage on the divider and converts it to exhaust gas temperature according to the programmed converter. The simplest error for the controller to detect is the disconnection or short-circuiting of the sensor – the voltage will reach a value outside the permissible range and the controller remembers the fault code. When performing a typical test with a diagnostic scanner, we look out for error codes directly related to the exhaust gas temperature sensor, such as. P0544, P0546, P0549, P2031, P2033, P247A. In the case of the aforementioned errors, it is also a good idea to check the wiring, including the electrical connector of the sensor, before replacing it.

It is much more difficult to diagnose a situation in which a sensor is malfunctioning, but its readings are within an acceptable range. In such a situation, one can resort to comparing the value read from the sensor with the physical temperature measured, for example, with a suitable thermometer. If this is not caught, a faulty exhaust gas temperature sensor will transmit incorrect information to the engine control unit. If this condition persists longer it can in some cases lead to costly damage to the particulate filter or turbocharger.

INDEPENDENT DIAGNOSTICS

To test the sensor independently, we need to measure its resistance and compare it with reference values. Such a measurement will be possible even with a multimeter, but it is necessary to know the characteristics of the sensor. Quite common PTC-type sensors are distinguished by a resistance of about 215 … 220Ω at room temperature. In this case, you can use easy-to-find tables of values for industrial Pt100 sensors, remembering to divide the resistance value by 2 beforehand. That is, for a resistance of 400Ω, we look in the Pt100 table for a value of 200Ω, which corresponds to about 266°C.

It will be more difficult with NTC sensors, whose characteristics vary widely. At room temperature, for example, it could be 25kΩ, and it could also be 6MΩ. Such a large resistance may prove to be a problem for the user of a simple multimeter with a 2MΩ range, who will be under the impression that the circuit is open.

Odkryj efektywność testera czujników! Zaawansowane narzędzie do precyzyjnych pomiarów czujników w motoryzacji. Idealne dla diagnostyki czujników w profesjonalnych zastosowaniach w warsztacie samochodowym.
When testing, it is necessary to know how the exhaust gas temperature sensor works - how an increase in exhaust gas temperature affects the resistance of the sensor.

A much more convenient method than a multimeter is to measure with the QST-5 sensor tester. In addition to many other types of sensors, it can successfully test exhaust gas temperature sensors. The advantage of the device is the simplicity of carrying out the measurement. After connecting the sensor and selecting the temperature sensor from the list of sensors, we can read the resistance of the sensor. When you select one of the available temperature scales from the list, you also get the converted temperature value. For PTC sensors, this will be the EGT-PTC scale, and for NTC sensors, the EGT-NTC scales labeled B, C and E. Support for three different types of sensors makes it possible to carry out temperature measurements on many popular vehicles.

SIMULATING HIGH FLUE GAS TEMPERATURES

Having the temperature measured, we can check the behavior of the sensor by heating it with a heat gun (preferably with temperature control) and observe the readings. We can also use a hot air soldering iron or a hot steam source as a high temperature source. Both types of sensors (PTC and NTC) respond with a change in resistance to changes in temperature. Recall: PTC sensors have a resistance that increases with temperature, while NTC sensors have a decreasing resistance.

Odkryj efektywność testera czujników! Zaawansowane narzędzie do precyzyjnych pomiarów czujników w motoryzacji. Idealne dla diagnostyki czujników w profesjonalnych zastosowaniach w warsztacie samochodowym.
By heating the exhaust gas temperature sensor, we observe how the simulated exhaust gas temperature affects the sensor parameters.

HOW TO FIX EXHAUST GAS TEMPERATURE SENSOR FAILURE?

The only repair method is to replace the sensor. This is, as we mentioned, a component that is subject to wear and tear under the operating conditions created by the exhaust system. We should not delay replacement, as malfunction of this small component can generate much higher costs if expensive components are damaged. When replacing the sensor, it is a good idea to lubricate the threads with an anti-seize compound and to tighten them to the correct torque as recommended by the vehicle manufacturer.

It is important to select the sensor carefully because sensors with different characteristics can look very similar. Some motors use sensors of different types: an NTC sensor and a PTC sensor, or use NTC-type sensors with different scales. If the wrong sensor is installed, an error will often not be reported. This is possible because the scales of the sensors partially overlap However, the measurement of the exhaust gas temperature in such a case will be incorrect, which after some time may result in engine problems.

list of PTC (Pt200) type EGT sensors - part numbers by brand

Alfa Romeo

51825680
51825681
51802893
51830621
51867072
55199541
55204763
55204765
55207108
55220508
55229330
55271704
55279495
059906088CP

DAF

1689812
1612300
1612372
1677124
1689811
1810690
1810691
3468052

Porsche

059906088BP
059906088BR
059906088BN

Renault Trucks

7420889280
7421412472

Saab

55575039

Scania

1882567
2265872
2253825

Seat

03G906088AC
03G906088AF
03G906088AM
03G906088D
03G906088E
03G906088F
03G906088L
03L906088AB
03L906088AJ
03L906088CC
03P906088D
03L906088FG
03P906088A
03P906088E
045906088D
045906088F
045906088G
045906088J
04L906088
04L906088BF
04L906088CE
04L906088DA
04L906088DH
04L906088E
04L906088K

Audi

036906088C
038906088A
038906088C
038906088D
038906088E
03G906088AF
03G906088AK
03G906088AP
03G906088BA
03G906088D
03G906088J
03G906088R
03L906088AB
03L906088AG
03L906088BS
03L906088BT
03L906088CC
03L906088CH
03L906088E
03L906088F
03L906088P
03L906088AJ
04L906088
04L906088AE
04L906088BD
04L906088BF
04L906088CE
04L906088DA
04L906088DH
04L906088E
04L906088K4
057906088A3
057906088B
057906088D
059906088A
059906088AA
059906088AC
059906088AE
059906088AK
059906088AT
059906088BB
059906088BH
059906088BJ
059906088BK
059906088BM
059906088C
059906088CE
059906088CP
059906088H
059906088K
059906088M
059906088P
059906088Q
059906088S
059906088T
06F906088D
07Z906088A
4G0906088AA
4G0906088AN
4G0906088H
4G0906088L
4H0906088F
4H0906088G
8K0906088
8K0906088C
8W0906088E
8W0906088F
8W0906088Q

Fiat

51779770
51791310
51799538
51807903
51825681
51825683
51861682
55197011
51917398
55190624
55199053
55199543
55200036
55200037
55203808
55204765
55208250
55212786
55218471
55228650
55243388
55271703
55271704

Ford

1792122 96050
8C3Z5J213D
8C3Z5J213B
AB3A-12B591-AA
AC3Z-5J213-B
AC3Z-5J213-C
BK2A-12B591-AB
CC1A-12B591-BB
EB3G-12B591-FA
EB3G-12B591-FB

Volvo

20451990
20889280
21126692
21164792
21225020
21412472
30729648
30751456
31293031
31293032
31293172
31303026
31319265
31319840
31319842
31370463
31370466
31370468
31370692
31431045
31431047
31431048
31431049
50422509

GM Chevrolet

12598444
12622555
12633560
12636612
12637488
25183660
25183664
25186658
55489472
55499997
55557600
55562433
55564270
55564977
55566185
55566575
55566631
55574183
55578722
55578800
55578799
96868940
96868946

GMC

12623113
12636612
12637488

Iveco

504102603
69502363
5801291815

Jeep

55254789
55271493

Lancia

55207108
55228650

Skoda

038906088B
03G906088AC
03G906088AF
03G906088AK
03G906088AN
03G906088D
03L906088AJ
03L906088CC
03L906088CH
03L906088P
03P906088A
03P906088C
03P906088D
045906088D
045906088F
045906088G
045906088J
04L906088BF
04L906088CE
04L906088DH
04L906088E
04L906088K
06F906088D

Smart

0009050832
0009051732

Suzuki

18213-79J60

Mercedes-Benz

0009050132
0009050332
0009050632
0009050701
0009050805
0009051405
0009052605
0009053300
0009053505
0009054305
0009055205
0009055608
0009056404
0009056704
0009056804
0009056904
0009057004
0009057104
0009057801
0009057901
0009058501
0009058700
0009058800
0009058804
0009058900
0009058904
0009059000
0019050600
0019050700
0019050900
0019052200
0019052300
0019052400
0019052799
0019052800
0019052900
0019053000
0051531028
0051531128
0051532028
0051532228
0051534128
0051534228
0051534528
0051539028
0051539228
0061530528
0061530628
0061530728
0071533428
0071536228
0071536328
0071536528
0071536628
0071536728
0071537428
0071537528
0071537628
0071537828
0071538428
0071538428
0071538628
0071538828
0071539027
0071539028
0071539128
0071539228
0071539428
0071539528
0071539628
0071539828
0071539928
0081532228
0081532728
0081532828
0081533428
0081533528
0081533628
0081533728
0081534028
0081534128

Opel

855255
855286
855287
855387
855410
855412
855425
855415
855457
855460
855505
855526
855574
1247292
1247634
1249073
25183663
4803548
4818659
5855377
5855388
55190617
55250523
55270986
55355404
55496933
55557466
55558578
55565652
55566086
55566621
55566817
55571194
55571362
55574938
55578800
55591173
95519373
96474598
96868946
96994636
96994638
55564977
55566185
55575039
55588650

Volkswagen

036906088C
038906088B
03G906088
03G906088AC
03G906088AF
03G906088AR
03G906088AT
03G906088D
03G906088E
03G906088F
03G906088L
03G906088K
03K906088B
03L906088AB
03L906088AF
03L906088AJ
03L906088AQ
03L906088AT
03L906088BN
03L906088BP
03L906088BQ
03L906088C
03L906088CC
03L906088CE
03L906088CH
03L906088CQ
03L906088DC
03L906088DE
03L906088DF
03L906088DJ
03L906088DN
03L906088DP
03L906088ED
03L906088EE
03L906088EF
03L906088EJ
03L906088EK
03L906088ES
03L906088FB
03L906088FE
03L906088FF
03L906088FG
03L906088FQ
03L906088GR
03L906088HB
03L906088HG
03L906088HK
03L906088J
03L906088JK
03L906088L
03L906088T
03L906088DH
03L906088DM
03L906088G
03P906088C
03P906088D
045906088D
045906088F
045906088G
045906088J
04L906088
04L906088AE
04L906088BD
04L906088BF
04L906088CE
04L906088CM
04L906088CN
04L906088CP
04L906088DA
04L906088DH
04L906088E
04L906088K4
057906088A3
059906088A
059906088AA
059906088AB
059906088AC
059906088AD
059906088BJ
059906088BP
059906088BR
059906088BN
059906088BS
059906088C
059906088CE
059906088CL
059906088CP
059906088K
059906088P
059906088S
059906088T
06F906088D
070906088
070906088A
070906088AA
070906088AC
070906088AD
070906088AE
070906088AF
070906088D
070906088E
076906088A
076906088C
076906088E
07Z906088A
07Z906088C
07Z906088N
07Z906088P

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