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 -48°C
5. Disconnect the four-pin wiring connector from the intake manifold pressure sensor with intake air temperature sensor (arrow) (the engine may stall) (fig. 4.30).
6. Shunt contacts 1 and 2 of the wiring connector using auxiliary wires from the VAG 1594 tester and observe the readings on the display (Fig. 4.34).
The display shows approximately 143°C:
- press "→";
- press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
- turn off the ignition;
- replace the intake manifold pressure sensor with the intake air temperature sensor.
The display shows approximately -48°C:
- press "→";
- press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
- turn off the ignition;
- connect the VAG 1598/38 tester to the engine control unit wiring harness (on the left in the engine compartment) (fig. 4.32). the control unit must remain disconnected;
- check the wire between the tester and the connector for open circuit: tester socket 108 and contact 1, tester socket 85 and contact 2 (fig. 4.33). Specified value: max. 1.5 Ohm.
- check the wires for short circuit to positive. Specified value: ∞ Ohms.
7. If no fault is found in the wires, then replace the intake manifold pressure sensor with the intake air temperature sensor.
Continue testing at 143°C
8. Disconnect the four-pin wiring connector from the intake manifold pressure sensor with intake air temperature sensor (arrow) (the engine may stall) (fig. 4.30). The display shows approximately -48°C:
- press "→";
- press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
- turn off the ignition;
- replace the intake manifold pressure sensor with the intake air temperature sensor.
The display shows approximately 143°C:
- press "→";
- press "06" to select the "Complete Output" function and confirm by pressing the "Q" button;
- turn off the ignition;
- connect the VAG 1598/38 tester to the engine control unit wiring harness (on the left in the engine compartment) (fig. 4.32). The control unit must remain disconnected;
- check the wire between the tester and the connector for open circuit: tester socket 108 and contact 1, tester socket 85 and contact 2 (fig. 4.33). Specified value: max. 1.5 Ohm.
- additionally check the wires for short circuit to the positive pole. Specified value: ∞ Ohms.
9. If no fault is found in the wires, then replace the intake manifold pressure sensor with the intake air temperature sensor.
Continue testing at ambient temperature
10. Remove the intake manifold pressure sensor with the intake air temperature sensor (the wiring connector remains connected) (Fig. 4.35).
11. Remember the temperature value in field 4 of the display.
(View the original article on the resource: VWManual)
12. Spray the sensor with cooling spray, watching the temperature reading. It should decrease.
13. Click "→".
14. Press "06" to select the "Complete Output" function and confirm by pressing the "Q" button.
15. If the specification values are not achieved, replace the intake manifold pressure sensor with the intake air temperature sensor.
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