Engine Coolant Temperature (ECT) Sensor, Checking
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.
- Fuses -1, 2, 3, 4 and 7- in protective housing (plenum chamber, left) 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
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Check 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 following table:
Indicated 1) Cause
approx. -40 degrees C Open circuit or short circuit to B+
approx. 140 degrees 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 must climb uniformly
NOTE:
- The temperature increases in increments of 1.0 degrees C.
- If the engine shows problems in certain temperature ranges and the temperature does not climb uniformly, the temperature signal is intermittent and the sensor must be replaced.
- Switch ignition off.
Continuation of test if indication is approx. -40 degrees C:
- Disconnect 2-pin connector from Engine Coolant Temperature (ECT) Sensor -G62- (arrow).
- Bridge terminals 1 + 2 of connector using the respective adapter cables and observe the indication on display.
If indication jumps to approx. 140 degrees C:
- End diagnostic and switch ignition off.
- Remove intake air hose between Mass Air Flow (MAF) sensor and throttle valve control module, item 1 .
- Replace Engine Coolant Temperature (ECT) Sensor -G62-.
WARNING:
- Cooling system is under pressure.
- Danger of scalding when opening!
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If indication remains at approx. -40 degrees C:
- End diagnostic and switch ignition off.
- Check wires according to wiring diagram.
Continuation of test if indication is approx. 140 degrees C:
- Disconnect 2-pin connector from Engine Coolant Temperature (ECT) Sensor -G62- (arrow).
If indication jumps to approx. -40 degrees C:
- End diagnostic and switch ignition off.
- Remove intake air hose between Mass Air Flow (MAF) sensor and throttle valve control module, item 1 .
- Replace Engine Coolant Temperature (ECT) Sensor -G62-.
WARNING:
- Cooling system is under pressure.
- Danger of scalding when opening!
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If indication remains at approx. 140 degrees C:
- End diagnostic 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 2-pin connector for open circuit according to wiring diagram.
Terminal 1 + socket 93
Terminal 2 + 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: Infinity Ohms
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If no malfunctions are found in wires:
- Measure resistance at Engine Coolant Temperature (ECT) Sensor -G62-.
- Range A displays resistance values for the temperature range of 0 to 50 degrees C, range B displays resistance values for the temperature range of 50 to 100 degrees C.
Read-out examples:
- 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 k Ohms
- 80 degrees C is in range B and corresponds to a resistance of 275 to 375 Ohms
If specified value is not obtained:
- Remove intake air hose between Mass Air Flow (MAF) sensor and throttle valve control module, item 1 .
- Replace Engine Coolant Temperature (ECT) Sensor -G62-.
WARNING:
- Cooling system is under pressure.
- Danger of scalding when opening!
- Erase DTC memory of Engine Control Module (ECM), 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-.