1. Disconnect 4-pin harness connector 1 from coolant temperature sensor 2 (pic. 3.35).
2. Measure the resistance between contacts 1 and 3 of the sensor.
3. The set value is shown in fig. 3.36. Area A shows resistance in the temperature range 0-50°C, area B shows resistance in the temperature range 50-100°C. For example, a temperature of 30°C corresponds to a resistance of 1500-2000 ohms; a temperature of 80°C corresponds to a resistance of 275-375 ohms.
4. If the specified value is not reached, replace sensor 2.
5. If the specified value is reached, connect the VAG 1598/30 tester to the wiring harness of the engine control unit. Check wires between tester and 4-pin connector for continuity: pin 1 + socket 17, pin 3 + socket 42 (fig 3.34). Set value: max. 1.5 ohm.
6. Additionally, check the wires for shorting one to the other, to «mass» vehicle and to the positive pole of the battery.
Specification resistance: ∞ Ohm.
7. If no fault is found in the wires, then replace the engine control unit.
Additional check for a fault recorded as «Sporadic malfunction S/P».
8. If this fault code is stored in memory as «Sporadic malfunction S/P»: additionally check the functionality of the sensor. To do this, the engine must be cold.
9. Connect tester VAG 1551 and dial «01» to select a function «Address word» engine control unit. The engine must be running at idle. The display should show the following information:
10. Click «08» to select a function «Reading a block of measured values» and confirm by pressing the button «Q». The display should show the following information:
11. Click «001» to select a function «Group 1 display» and press «Q». The display should show the following information:
12. Check the value in field 2 with the engine running. The temperature should rise smoothly without delay.
- If the value on the tester display jumps from 2 to 5°C, this is caused by the control unit, and not by a sensor malfunction.
- If in some temperature ranges there are interruptions in the operation of the engine and the temperature of the coolant does not increase smoothly, but intermittently, this means that there is a signal loss and the sensor must be replaced.
13. Click «→».
14. Click «06» to select a function «Output Completion» and confirm by pressing the button «Q».
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