Audi A4 B6 1.8 Coolant Temperature Sensor in Place

ENGINE COOLANT TEMPERATURE SENSOR (ECT)

General description
      The engine coolant temperature sensor is temperature-variable resistor, which normally has a negative temperature coefficient. It is a two-wire thermistor immersed in coolant and measures its temperature. The onboard estimator uses the signal of ECT as the main correction cistron when calculating the ignition advance and the injection elapsing.

Appearance
The ECT sensor is shown on fig. 1.

Fig. 1

Working principle of the ECT sensor
      In order to convert the ECT resistance variation to voltage variation, which is further candy past the ECU, the ECT sensor is connected in a circuit typically supplied with a reference voltage of +5V. In cold engine and an ambience temperature of 20 ºC the sensor resistance is between 2000Ω and 3000Ω. Subsequently the engine start, coolant temperature begins to rising. ECT gradually heats and its resistance reduces proportionately. At 90 ºC its resistance is in the range of 200Ω to 300Ω.
Thereby, a coolant temperature dependent variable voltage signal is send to the onboard computer.

Types of ECT sensors

• With negative temperature coefficient. These are the almost popular sensors used in cars. Their resistance decreases with the increment of the temperature.
• With positive temperature coefficient. Used in some older systems, such every bit Renix. Here the voltage and the resistance are increasing with the raise of the temperature.

Process for verification the functionality of the ECT sensor
—  Sensor with negative temperature coefficient —
Exam with voltmeter

• Open the protective rubber cap on the connector of the cooling system temperature sensor.
• Connect the negative wire of the voltmeter to the chassis footing.
• Determine which are the bespeak and the footing terminals.
• Connect the positive wire of the voltmeter is to the ECT bespeak terminal.
• Starting time the engine form common cold state.
• Depending on the temperature, voltage readings should be in the range of 2V to 3V. The human relationship betwixt the voltage and the temperature is shown in Table-one.
• Check whether the ECT voltage betoken corresponds to the temperature. You will need a thermometer for the purpose.
• Commencement the engine and warm it to the operating temperature. During engine warming the voltage should decrease in accord with the values given in Table-ane.
• Mutual problem is that the output resistance (and voltage) changes incorrectly beyond its normal range. The normal value of the ECT sensor voltage is 2V at cold engine and 0.5V at warm engine. A defect sensor can indicate a voltage of 1.5V at cold engine and ane.25V at warm engine, thus causing difficulties of starting a cold engine and a presence of rich fuel mixture when the engine is warm. This will not generate any fault codes (if the onboard controller is not programmed to detect voltage changes) since the sensor continues to operate within its pattern parameters. If such defect is plant, the ECT sensor must be replaced.
•  If the ECT voltage signal is equal to 0V (lack of power supply or there is a brusque circuit to the ground) or if it is five.0V - we accept an open excursion.

Temperature, ºС	Resistance, Ω	Voltage, Five
0	4800 - 6600	iv.00 – 4.l
10	4000	3.75 – 4.00
20	2200 - 2800	three.00 – 3.fifty
30	1300	3.25
40	1000 – 1200	2.50 – 3.00
50	1000	2.l
60	800	two.00 – 2.50
80	270 - 380	1.00 – 1.thirty
110		0.50
Broken circuit		v.0 ± 0.1
short circuit to the ground		0

Table i
NOTE: This is a typical example, but this does not mean that the values shown to a higher place are real and must be obtained in the procedure of verification of a specific system.

Possible sensor failures:
-- The voltage of the ECT indicate terminal is equal to 0V.

• Cheque sensor terminals for short circuit to ground.
• Check the integrity of the signal wires between the sensor and the onboard controller.
• If all wires are right, but there is no output voltage from the onboard controller, you have to verify all power supply and footing connections of the onboard controller. If supply voltages and grounds are adept, the onboard controller itself falls under suspicion.

-- The voltage of ECT signal terminal is equal to v.0V
The voltage has such a value when an open circuit is present and may be obtained in 1 of the following weather:

• the signal terminal of the ECT sensor does non provide connexion to the sensor;
• sensor circuit is open up;
• sensor's ground circuit is open.

-- The voltage signal or the reference voltage is equal to the machine battery voltage.
Cheque brusque excursion in the wire, connected to the positive last of the automobile battery or the power supply wire.

—  Sensor with negative temperature coefficient —
Check with ohmmeter with ECT sensor detached from the car

• Place the sensor in a suitable water container and measure the water temperature.
• Measure out the sensor'south resistance and compare it with the values given in Table-1, showing the relationship between the resistance and the temperature.
• Heat the h2o and take measurements periodically as well as the resistance of the sensor. Compare the results with those in table 1.

—  Sensor with negative temperature coefficient —
Voltage measurement with oscilloscope

• Connect the active end of the oscilloscope probe to the signal terminal of the sensor and the ground probe - to chassis footing.
• Set the trigger sweep of the oscilloscope in a continuous measurement mode (registration of slowly irresolute signals).
• Identify the sensor in a suitable heated h2o container.
  Later on a few minutes of measurement, during the water heating fourth dimension, oscilloscope screen will show the sensor'southward voltage modify curve (Fig. ii). Pay attention to the measuring time - it is most x minutes.
• Information technology is desirable to continuously measure the temperature of the heated water with a thermometer and compare it with the values listed in table 1.

Fig. 2

— Sensor with a positive temperature coefficient —
      ECT sensor with a positive temperature coefficient of resistance is a thermistor whose resistance increases with the rising of the temperature. Information technology is used in a small number of systems (mainly in Renault cars).
      The overall method of verification is similar to the method for checking a sensor with negative temperature coefficient, described higher up. Received measurement data tin be compared with the data given in Table 2 showing the relationship between the resistance and the temperature of the sensor.

Temperature, ºС	Resistance, Ω	Voltage, V
0	254 - 266
xx	283 - 297	0.6 – 0.8
80	383 - 397	1.0 – 1.2
open up excursion		5.0 ± 0.1
short excursion to ground		0

Table 2

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Audi A4 B6 1.8 Coolant Temperature Sensor in Place

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