Checking the coolant temperature sensor (VW Lt 2d)

1. Connect the VAG 1551 tester and, by entering "01" "Engine electronics", select the engine control unit. The engine should be idling. The display should show the following information:

• Fast data exchange HELP
• Dial function XX

2. Press "08" to select the "Read Block of Measured Values" function and confirm with the "Q" button. The display should show the following information:

• Reading the measured value block HELP
• Enter group number XXX

3. Press "001" to select the "Display Group 001" function and press "Q". The display should show the following information:

Reading a block of measured values 1 → 1 2 3 4

4. With the engine running, observe the coolant temperature reading in field 2 of the display. It should increase slowly, without pauses. If the displayed temperature differs significantly from the temperature indicated by the sensor, check the sensor wire's transmission resistance.

5. Click "→".

6. Press "06" to select the "Complete Output" function and confirm by pressing the "Q" button.

7. Turn off the ignition.

8. If the numerical value does not rise evenly, replace the coolant temperature sensor.

9. If the numerical value rises evenly, but there is still a fault in the fault memory, connect the VAG 1598/26 tester.

10. Disconnect the 3-pin wiring connector from the coolant temperature sensor (arrow) (figure 2.79).





11. Check the wires between the tester and the 3-pin connector for open circuit using the wiring diagram (figure 2.80): contact 2 and socket 7 (blue), contact 1 and socket 9 (blue).



Wire resistance: 1.5 ohms

12. Check the wire between the tester and contact 2 of the connector for a short circuit with the wire of contact 1 and to ground, using the wiring diagram.

13. Also check the short circuit of the wires to the positive terminal of the battery. Set value: ∞ 0m.

14. If there is no damage to the wires, check the resistance between contacts 1 and 2 of the coolant temperature sensor. The specified values are given in Table 2.6.

Table 2.6. Specified resistance values between the contacts of the coolant temperature sensor

Temperature	Resistance	Temperature	Resistance
20°C	2.38-3.63 kOhm	70°C	414-456 Ohm
30°C	1.62-1.79 kOhm	80°C	310-341 Ohm
40°C	1.11-1.23 kOhm	90°C	233-257 Ohm
50°C	790-870 Ohm	100°C	176-194 Ohm
60°C	570-630 Ohm

15. Reconnect the connector

16. If the specified value is not achieved, replace the Motronic control unit.

17. Disconnect the VAG 1593/26 tester.