Checking the inlet air temperature sensor (VW Polo 3)

1. Connect the VAG 1551 tester and dial "01" to select the "Address word" function of the engine control unit. The engine should be idling. The display should show the following information:

2. Press "08" to select the "Read measured value block" function and confirm by pressing the "Q" button. The display should show the following information:


3. Press "002" to select the "Display Group 2" function and press "Q". The display should show the following information:


4. Read the incoming air temperature in field 4 of the display.

Continue testing at -55°C

5. Disconnect wiring connector 1 from sensor 2 (Fig. 5.53).



6. Shunt contacts 1 and 4 of the wiring connector using auxiliary wires from the VAG 1594 tester and observe the readings on the display.

7. The display shows approximately 130°C or higher: replace the injector support bracket together with the intake air temperature sensor.

8. The display shows approximately -55°C:

• press "→";
• press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
• turn off the ignition;
• connect the VAG 1598/18 tester to the engine control unit wiring harness;
• check the wire between the tester and the connector for an open circuit: socket 43 of the tester and contact 4 of the four-pin wiring connector (fig. 5.45). Specified value: max. 1.5 Ohm.
• check the wires for short circuit to positive. Specified value: ∞ Ohms.
• check the wire between the tester and the connector for continuity: socket 17 of the tester and contact 1 of the four-pin wiring connector. Specified value: max. 1.5 ohms.

9. If no fault is found in the wires, then replace the engine control unit.

Continue testing at 130°C and above

10. Disconnect wiring connector 1 from sensor 2 (Fig. 5.54).




11. The display shows approximately -55°C: replace the injector support bracket together with the inlet air temperature sensor.

12. The display shows approximately 130°C and above:

• press "→";
• press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
• turn off the ignition;
• disconnect the wiring connector from the engine control unit;
• check the wire to contact 4 of the four-pin connector of the engine control unit wiring for a short to contact 1 of the wire and to ground. Specified value: ∞ Ohms.

13. If no fault is found in the wires, then replace the engine control unit.

Continue testing at ambient temperature

14. Spray the cooling spray (arrow) onto the sensor, observing the temperature reading (Fig. 5.55). It should decrease.



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15. Click "→".

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