Circuit/System Description
Note. The radiator coolant temperature sensor is referred to as B34B Engine Coolant Temperature Sensor 2 in schematics and other areas.
The radiator coolant temperature (RCT) sensor is a variable resistor that measures the temperature of the engine coolant in the radiator. This diagnostic checks for an open, short to ground or an intermittent circuit condition between the engine control module (ECM) and RCT sensor.
The following table illustrates the difference between temperature, resistance, and voltage
| RCT | RCT Resistance | RCT Signal Voltage |
|---|---|---|
| Cold | High | High |
| Warm | Low | Low |
The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
The engine control module (ECM) controls the pulse width modulated (PWM) thermostat. The thermostat controls coolant flow and regulates the engine operating temperature. Ignition voltage is supplied directly to the thermostat through a fuse. The ECM controls the thermostat by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.
The engine control module (ECM) monitors temperature difference between the engine coolant temperature (ECT) sensor and the radiator coolant temperature (RCT) sensor during a cold start-up. The purpose of this diagnostic is to analyze the engine coolant thermostat for being stuck open.
The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
Cooling Fan Description and Operation
The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
Low Speed Operation
The ECM applies ground at the FAN 1 control circuit for the coil side of the cooling fan relay. The energized cooling fan relay completes a ground, through the switch side of the relay, for the coils of the cooling fan low speed relay and the cooling fan speed control relay. The speed control relay activates and supplies B+ to the coil side of the cooling fan high speed relay. The high speed relay remains inactive because the ECM is not commanding the FAN 2 control circuit ON. The energized low speed relay switch closes to supply B+ through the internal low speed resistor of the engine cooling fan motor. The result is cooling fan operation at a reduced speed.
Medium Speed Operation
The ECM applies ground at the FAN 2 control circuit for the coil side of the cooling fan high speed, and medium speed relays. The high speed relay remains inactive because the ECM is not commanding the FAN 1 control circuit ON. The energized medium speed relay switch closes to supply B+ through the internal medium speed resistor of the engine cooling fan motor. The result is cooling fan operation at a medium speed.
High Speed Operation
The ECM applies ground at the FAN 1 control circuit for the coil side of the cooling fan relay. The energized cooling fan relay completes a ground, through the switch side of the relay, for the coil of the cooling fan speed control relay. The energized speed control relay switch closes to supply B+ to the coil side of cooling fan high speed relay. Simultaneously, the ECM applies ground at the FAN 2 control circuit for the coil side of the cooling fan high speed relay. The energized high speed relay switch closes to supply B+ directly to the engine cooling fan motor, by-passing the fans internal resistors. The result is cooling fan operation at full speed.
The cooling systems function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly. Refer to the following illustration for the components in the system and the basic flow path of the coolant.
Scheme 2
Note. See arrows for coolant flow order.
The cooling system consists of the following components
- Heater (1)
- Surge Tank (2)
- Water Outlet (3)
- Engine Oil Cooler (4)
- Cooling Fan (5)
- Radiator (6)
- Turbocharger (7)
- Engine Coolant Thermostat (8)
- Engine Block (9)
- Water Pump (10)
Scheme 3
Water pump is a component of the engine cooling system and circulated the coolant from each cooling circuit components. This water pump consists of sealing, bearing, pulley (1) and housing (2) and is driven by the drive belt to loose noise to water pump pulley. Water pump apply drain hole cup to cap to prevent coolant leakage for customers. Water pump is not open impeller type but closed plastic impeller type (3) to increase the cooling efficiency.
Scheme 4
The Thermostat is a regular part of the Thermostat Housing (1). The thermostat controls coolant flowing. It is a grid controlled electronic wax pellet type. By coolant temperature and / or applying current, the wax-pellet of the thermostat is molten what leads to the opening of the thermostat. That allows the coolant to flow through the radiator. The electronic heating of the thermostat is controlled by the engine control unit. The thermostat begins to open with 0V at 103°C (217°F) and with 12V at 80°C (176°F). It is fully open at 117°C (243°F). Whether the thermostat opening is supported by the electronic heating or not depends on load conditions which are defined as parameters in the grid.