Engine Coolant Temperature Sensor, Checking

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 .

Special tools and workshop equipment required 

• Multimeter.
• jumper wire.
• Wiring diagram.

Test requirements 

• The Motronic Engine Control Module (ECM) - J623- fuses OK.
• 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 connections between engine/transmission/chassis OK.
• Ignition switched off.
• Engine cold.

Start diagnosis 

Engine must be at room temperature.

-- Connect the scan tool.

-- Switch the ignition on.

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

Diagnostic text		Specified value
Coolant temperature		Approx. ambient temperature

If the specified value was obtained:

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

The temperature value must increase uniformly in increments of approximately 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 the Repair information.

Checking internal resistance 

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

-- 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 value:

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 the specified values were Not obtained:

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

If the specified values were obtained:

Checking wiring 

If the manufacturers test box is being used, perform the following step.

-- Install the test box.

If the manufacturers test box is not being used, perform the following step.

-- Remove the Motronic Engine Control Module (ECM) -J623-. Refer to the Repair information.

-- Using a multimeter, check the Engine Coolant Temperature (ECT) Sensor - G62- electrical harness connector terminals to the Motronic Engine Control Module (ECM) -J623- electrical harness connector T60 terminals for a circuit fault, refer to the chart below.

Engine Coolant Temperature (ECT) Sensor - G62- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T60 terminals or test box socket
1	43
2	54

Specified values: 1.5 Ω Max.

If the specified value was Not obtained:

-- Check the wiring for an open, high resistance or short circuit.

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and sensor resistance is OK:

-- Replace the Motronic Engine Control Module (ECM) -J623-. Refer to the Repair information.

Final procedures 

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .