1 Coolant pump
2 EGR cooler
3 Heater core
4 Thermostat housing
5 Bypass solenoid valve
6 Thermostat
7 Shutoff solenoid valve
8 Radiator
9 Oil/coolant heat exchanger
10 Coolant reservoir
Some versions with Siemens common rail system are equipped with an engine warm-up regulator. This regulator permits faster warming up of the engine and reduces the increased pollutant emissions during the warm-up phase. A bypass solenoid valve has been integrated in the coolant system for this purpose. Like the ECT sensor, the bypass solenoid valve is located in the thermostat housing. Actuation of the bypass solenoid valve is via the PCM, which performs regulation in accordance with the coolant temperature signal. A conventional thermostat, which works according to the expanding material principle, is also used for engine temperature regulation. Another component is the shutoff solenoid valve. This limits the flow of coolant to the coolant expansion tank during the warm-up phase.
Note:
โข in January 2004 the PCM software was changed. This modification to the software (starting with software bearing the suffix NB) meant that the shutoff solenoid valve is no longer controlled. From March 2004, production with the shutoff solenoid valve ceased altogether.
โข For this reason the shutoff solenoid valve is no longer
covered in the following function description.
First Phase
1 Bypass solenoid valve
2 Thermostat
In the first phase, the bypass solenoid valve and the thermostat are closed. The coolant is fed by the coolant pump through the engine and the oil cooler directly to the heat exchanger. It is then returned to the coolant pump via the EGR cooler.
Second Phase
1 Bypass solenoid valve
2 Thermostat
Above a certain coolant temperature, the bypass solenoid valve begins to open and remains open until engine operating temperature is reached. Part of the coolant now flows directly back to the coolant pump while the remainder is routed via the heat exchanger. The thermostat remains closed.
Third phase
1 Bypass solenoid valve
2 Thermostat
When the thermostat opening temperature is reached, the thermostat opens. At the same time, the bypass solenoid valve is closed. Coolant is now also routed through the radiator (large coolant circuit).
Values
Power supply voltage of bypass solenoid valve approx. 12 V.
Effects of faults
In the case of a fault, the cooling fan runs at maximum power. The air conditioning system is also switched off, or switching on the air conditioning system is disabled
Diagnosis
The bypass solenoid valve is only monitored for short and open circuit. In this way, a blocked solenoid valve (open or closed state) can be detected by the PCM. If a “control circuit fault – low” is detected, the PCM interprets this as a short to ground or an open control loop.
If a “control circuit fault – high” is detected, the PCM interprets this as a short to positive.
Bypass solenoid valve faults have no effect on exhaust gas emissions. Therefore, this is a non MIL active component.
Possible diagnostic trouble codes:
โข P2682 (short to ground / open control loop),
โข P2683 (short to positive).