Bosch Motronic - Component Datasheet

Coolant Temperature Sensor (G62)

This device is also known as the Engine Coolant Temperature sensor (or ECT for short). Located on the rear of the cylinder head, G62 provides the ECU with a signal pertaining to the coolant temperature. This is needed to provide adjustments to ignition timing; injection timing during cold or hot starts. It is also used to ensure proper fuel enrichment in the warm-up cycle and cold idle stabilisation.

G62 is a negative temperature coefficient (NTC) thermistor. That means the resistance value decreases with an increase in temperature.

As such, when it fails or is disconnected, one would expect the ECU to interpret settings for a cold engine. However a little more intelligence is built into the ECU such that a substitute value is utilised with knowledge of the intake air temperature measured at G42. This is a good thing as the subsequent rich running (as if the engine was cold) would provide both poor performance and poor fuel economy.

  • When air temp exceeds 0 degrees C, the substitute coolant temperature is 80 degrees C.
  • When starting the engine with air temp lower than 0 degrees C, this air temperature is assumed as the substitute value for coolant temperature for three minutes before a new substitute value of 80 degrees C is adopted.

    Application 3B, ABY
    Audi Part Number 035.919.369 M
    Bosch Part Number

Testing the Engine Coolant Temp sensor (ECT), G62

Using a DMM set for resistance, and the engine cold at an ambient air temperature of 20 degrees Celsius, expect a value of approx 2500 ohms across the two pins of G62.

Actually, fiddling about to get the DMM probes in there is no mean feat. It is much easier to use a 2-pin AMP connector attached to the sensor with a short length of cable to make this test.

The figure below shows the temperature - resistance graph for G62. This is very useful for tests across at a wide range of values.

G62 Graph

Last Updated 11th November 2007