Engine Coolant Temperature Sensor On Radiator, Checking

Special tools and workshop equipment required 

• Multimeter.
• jumper wire.
• Wiring diagram.

Test requirements

• The Motronic Engine Control Module (ECM) - J623- fuses OK.
  Fig 1: Fuses On E-Box In Engine Compartment, Left Side

  
• 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

Function test

-- 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+)	ENGINE COOLANT TEMPERATURE SENSOR ON RADIATOR, CHECKING
approx. 140.0° C	Short circuit to Ground (GND)	ENGINE COOLANT TEMPERATURE SENSOR ON RADIATOR, CHECKING

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 (on radiator)

Checking internal resistance

-- Disconnect the Engine Coolant Temperature (ECT) Sensor (on radiator) -G83- electrical harness connector -10-.

-- Using a multimeter, check the Engine Coolant Temperature (ECT) Sensor (on radiator) -G83- 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 (on radiator).

Testing if display is approx. - 40.0° C. Refer to ENGINE COOLANT TEMPERATURE SENSOR ON RADIATOR, CHECKING .

-- Disconnect the Engine Coolant Temperature (ECT) Sensor (on radiator) -G83- electrical harness connector -1-.

-- Using a jumper wire, connect the Engine Coolant Temperature (ECT) Sensor (on radiator) -G83- electrical harness connector terminals 1 to 2.

-- Check the value indicated on the scan tool display.

If the value jumps to approx. 140.0° C

-- End diagnosis and switch the ignition off.

-- Replace the the Engine Coolant Temperature (ECT) Sensor (on radiator)

If indication remains at approx. -40.0° C:

-- Testing if display approx. 140.0° C. Refer to ENGINE COOLANT TEMPERATURE SENSOR ON RADIATOR, CHECKING .

-- Disconnect the Engine Coolant Temperature (ECT) Sensor (on radiator) -G83- electrical harness connector -1-.

If indication jumps to approx. -40.0° C:

-- End diagnosis and switch ignition off.

-- Replace the the Engine Coolant Temperature (ECT) Sensor (on radiator)

If indication remains at approx. 140.0° C:

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 Engine Control Module (ECM) -J623-. Refer to appropriate service manual.

-- Using a Multimeter --, check the Engine Coolant Temperature (ECT) Sensor (on radiator) - G83- electrical harness connector terminals to the Motronic Engine Control Module (ECM) -J623- electrical harness connector T94 terminals for an open circuit according to the wiring diagram.

Engine Coolant Temperature (ECT) Sensor (on radiator) - G83- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T94 terminals or test box socket
1	26
2	12

Specified value: 1.5 Ω Max.

If the specification was not obtained:

-- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

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

-- If necessary, repair the faulty wiring connection.

-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY 

-- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to READINESS CODE .

-- End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

-- Replace the Motronic Engine Control Module (ECM) -J623-. Refer to appropriate service manual.

-- Assembly is performed in the reverse of the removal.

-- If ECT Sensor G62, Engine Coolant Temperature (ECT) Sensor (on radiator) G83and Motronic Engine Control Module (ECM)J623have no malfunctions, inspect Coolant Fans V7 & V177; Coolant Fan Control Modules J293 & J671. If resistance and voltage checks are not acceptable, repair as required

-- If resistance and voltage checks are satisfactory, replace affected Coolant Fan & Control Module (serviced as an assembly).

Final procedures

After 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 .