Engine Coolant Temperature Sensor, Checking: Notes

Special tools and workshop equipment required 

• Multimeter.
• jumper wire.
• Wiring diagram.

Test requirements 

• The Motronic Engine Control Module (ECM) - J220- fuses OK.
  Fig 1: Fuses On E-Box In Engine Compartment, Left Side

  Courtesy of AUDI OF AMERICA, LLC
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• A/C switched off.
• Ground (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.
• Engine cold.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK 

Start diagnosis 

-- Connect the scan tool.

-- Switch the ignition on.

-- Using the scan tool, check the coolant temperature:

Diagnostic text		Specified value
Coolant temperature		Approx. coolant temperature

If the specified value is not obtained:

-- Continue test according to the following table:

Indicated	Cause	Test
approx. - 40.0° C	Open circuit or short circuit to (B+)	TESTING IF DISPLAY IS APPROX. - 40.0 °C
approx. 140.0° C	Short circuit to Ground (GND)	TESTING IF DISPLAY APPROX. 140.0 °C

If the specified value was obtained:

-- Start the engine and let it run at idle.

The temperature value must increase uniformly in increments of 1.0° C.

If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent.

-- Replace the Engine Coolant Temperature (ECT) Sensor - G62-. Refer to Repair information.

Checking internal resistance 

-- Disconnect the Engine Coolant Temperature (ECT) Sensor -G62- electrical harness connector -arrow-.

-- Using a Multimeter, check the Engine Coolant Temperature (ECT) Sensor -G62- terminals 1 to 2 for resistance.

Use the chart below for the specified values:

• Area A: Resistance values 0 to 50 °C.
• Area B: Resistance values 50 to 100 °C.

Specified values:

• Range A, 30 °C equals a resistance of 1.5 to 2.0 kΩ
• Range B, 80 °C equals a resistance of 275 to 375Ω

If any of the specified values was not obtained:

-- Replace the Engine Coolant Temperature (ECT) Sensor - G62-. Refer to Repair information.