With Generic Scan Tool

Engine Coolant Temperature (ECT) Sensor, Checking

NOTE: Use only gold-plated terminals when servicing terminals in harness connector of sensor.

Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements





- The respective fuses of Motronic Engine Control Module (ECM) -J220- must be OK.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- For vehicles with automatic transmission, selector lever must be in position -P- or -N-.
- Engine must be cold.

Function test, vehicles with engine code AVH, AZG
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select the measuring value "PID 05: Coolant temperature".
- Check specified value of coolant temperature.







If specified value is not obtained:
- Continue test according to the given table:

Indicated 1) Cause
approx. -40.0 degree C Open circuit or short circuit to B+
approx. 140.0 degree C Short circuit to Ground (GND)

1) If a temperature is indicated which differs greatly from ambient temperature of sensor, check sensor wires for contact resistance.

If specified value is obtained:
- Start engine and let run at idle. The temperature should climb uniformly


NOTE:
- The temperature increases in increments of 1.0 degree C.
- If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent and the sensor should be replaced.


Continuation of test if indication is approx. -40.0 degree C:







- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2- (arrow)







- Bridge terminals 3 + 4 of connector using the respective adapter cables and observe the indication on display.

If indication jumps to approx. 140.0 degree C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) sensor (G62).
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If indication remains at approx. -40.0 degree C:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.

Continuation of test if indication is approx. 140.0 degree C:







- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2- (arrow)

If indication jumps to approx. -40.0 degree C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) sensor (G62).
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If indication remains at approx. 140.0 degree C:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.

Checking wiring
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test







- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.

Terminal 3 + socket 93
Terminal 4 + socket 108

Wire resistance: max: 1.5 Ohms

- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+. Specified value: Infinite Ohms

If no malfunctions are found in wires:







- Measure resistance at Engine Coolant Temperature (ECT) sensor -G62-, terminals C (signal) and D (Ground -GND-).







Range A displays resistance values for the temperature range of 0 to 50 degree C, range B displays resistance values for the temperature range of 50 to 100 degree C.

Read-out examples:
- 30 degree C is in range A and corresponds to a resistance of 1.5 to 2.0 kOhms
- 80 degree C is in range B and corresponds to a resistance of 275 to 375 Ohms

If specified value is not obtained:
- Replace Engine Coolant Temperature (ECT) sensor -G62-.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Motronic Engine Control Module (ECM) -J220-.