Engine Coolant Temperature Sensor, Checking

Special tools and workshop equipment required 

• Multimeter VAG 1526 or Multimeter VAG 1715
• Connector test kit VAG 1594
• Wiring diagram

Test requirements 

• Fuses in E-box (plenum chamber, left) must be OK: Refer to appropriate SYSTEMS WIRING DIAGRAM
  Fig 1: Identifying Fuses In E-Box (Plenum Chamber, Left)

  Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.
• Ground (GND) connections between engine and chassis 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 P.
• Engine must be cold.

Function test 

-- Connect diagnostic tester.

-- 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:

PID		Diagnostic text		Specified value:
05:		Coolant temperature		approx. coolant temperature

If specified value is not obtained:

-- Continue test according to the following table:

Indicated (1)	Cause	Continue testing
approx. -40 °C	Open circuit or short circuit to B+
approx. 140 °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

-- Switch ignition off.

Continuation of test if indication is approx. -40° 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 temperature jumps to approx. 140° 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.

-- Generate readiness code.

If indication remains at approx. -40° C:

-- End diagnosis and switch ignition off.

-- Check wires according to wiring diagram.

Continuation of test if indication is approx. 140° C:

-- Disconnect 2-pin connector from Engine Coolant Temperature (ECT) sensor -G62- (arrow).

If indication jumps to approx. -40° 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.

-- Generate readiness code.

If temperature remains at approx. 140° 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.

-- 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 Ω

-- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+.

Specified value: ∞ Ω

-- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.

-- Generate readiness code.

If no malfunctions are found in wires:

-- Replace Engine Coolant Temperature (ECT) Sensor -G62-.

-- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.

-- Generate readiness code.

If no malfunctions are detected in the wires and the resistance values are OK:

-- Replace Motronic Engine Control Module (ECM) -J220-.

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 .