Volvo TAD650VE, Руководство по ремонту

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Group 30: Electrical system Diagnostic Trouble Codes
67
Circuit description
The coolant temperature sensor consists of a ther-
mistor which forms a closed circuit with an internal re-
sistor in the engine control unit (EMS 2) via the en-
gine interface. The thermistor resistor changes in a
non-linear manner, depending on the coolant tempera-
ture. The EMS 2 provides the circuit with a reference
voltage of +5 Volt. The EMS 2 measures the voltage
drop over the thermistor via pin B27 and pin B18 on
the EMS 2. Pin 1 on the sensor is connected to bat-
tery negative via pin B18 on the EMS 2. When the
coolant is cold, the thermistor resistance is high and
the EMS 2 senses a high voltage drop. As the coolant
warms up, the resistance in the thermistor falls and
the voltage drop across it falls.
Fault tracing
FMI 0: Coolant temperature is too high
Conditions for fault code:
Coolant water temperature exceeds the set value of
the engine protection.
Possible reason:
• Coolant level too low.
• Dust or dirt on the outside of the radiator.
• Drive belt is not properly adjusted.
• There is air in the coolant water system.
• Faulty thermostat.
• Faulty temperature sensor.
• Clogged cooling water system.
Suitable action:
1. Check coolant level.
2. Check outside of the radiator for dust and dirt.
3. Check drive belt adjustment.
4. Bleed coolant water system.
5. If low coolant level check coolant water system for
leakage by a pressure test.
6. Check coolant pressure valve in the coolant cup
or try with another coolant cup.
7. Check coolant water thermostat or change cool-
ant water thermostat.
8. Check function of coolant temperature sensor.
9. Clean cooling water system.
skall vara 18 ej 10
coolant tem-
perture
splice
engine
interface
Note! Only TAD 650, 660, 750, 760 has an engine interface. On
TAD 734 the wiring to the EMS 2 is the same but without any en-
gine interface.