Engine Coolant Temperature Sensor, Checking: Notes

Observe all safety precautions: SAFETY PRECAUTIONS 

View clean working conditions: CLEAN WORKING CONDITIONS 

Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .

Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.

For wiring diagrams, component locations, and connector views, Refer to the applicable system wiring diagram.

Special tools and workshop equipment required 

• Generic scan tool
• Multimeter
• Wiring diagram

Test requirements 

• The Motronic Engine Control Module (ECM) - J623- 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 

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 the Engine Coolant Temperature (ECT) Sensor - G62-. Refer to the appropriate service 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:

Specified values:

ECT Temperature vs Resistance
Temp (C)	min value ohms	max value ohms
- 40	36816	43714
- 35	28840	33978
- 25	17680	20530
- 15	10940	12534
- 5	6897	7804
0	5535	6226
5	4443	4970
15	2923	3235
25	1978	2167
35	1369	1486
45	965	1039
55	692	738
65	503	533
75	372	392
85	279	292
95	213	223
105	164	172
115	127	134
125	99	106
135	78	84

If any of the specified values was not obtained:

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