Cooling Fan Control 3.4L (LA1)
The engine cooling fans are controlled by the body control module (BCM) and the powertrain control module (PCM). The BCM sends a class 2 message to the PCM requesting cooling fan operation. If there is a class 2 communication malfunction between the BCM and the PCM. The PCM will operate the engine cooling fans independently of the BCM.
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the PCM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the engine wiring harness junction block. The ground path is provided at G101.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the FAN CONT #1 relay coil, closes the relay contacts, and supplies battery positive voltage from the FAN CONT #1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the FAN CONT #2 relay and the left cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the FAN CONT #1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the FAN CONT #2 relay and the FAN CONT #3 relay through the high speed cooling fan relay control circuit. This energizes the FAN CONT #2 relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the FAN CONT #3 relay coil is energized closing the relay contacts and provides battery positive voltage from the FAN CONT #2 fuse on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
The BCM will request low speed cooling fan operation from the PCM under the following conditions:
| • | Engine coolant temperature exceeds approximately 103°C (217°F). |
| • | When A/C is requested and the ambient temperature is more than 10°C (50°F). |
| • | A/C refrigerant pressure exceeds 1310 kPa (190 psi). |
| • | After the vehicle is shut off if the engine coolant temperature at key-off is more than 117°C (243°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes. |
The BCM will request high speed cooling fan operation from the PCM under the following conditions:
| • | Engine coolant temperature reaches 110°C (230°F). |
| • | A/C refrigerant pressure exceeds 1655 kPa (240 psi). |
| • | When certain DTCs set. |
Cooling Fan Control 3.8L (L36/L67)
The engine cooling fans are controlled by the body control module (BCM) and the powertrain control module (PCM). The BCM sends a class 2 message to the PCM requesting cooling fan operation. If there is a class 2 communication malfunction between the BCM and the PCM. The PCM will operate the engine cooling fans independently of the BCM.
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the PCM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the engine wiring harness junction block. The ground path is provided at G101.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the FAN CONT #1 relay coil, closes the relay contacts, and supplies battery positive voltage from the FAN CONT #1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the FAN CONT #2 relay and the left cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the FAN CONT #1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the FAN CONT #2 relay and the FAN CONT #3 relay through the high speed cooling fan relay control circuit. This energizes the FAN CONT #2 relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the FAN CONT #3 relay coil is energized closing the relay contacts and provides battery positive voltage from the FAN CONT #2 fuse on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
The BCM will request low speed cooling fan operation from the PCM under the following conditions:
| • | Engine coolant temperature exceeds approximately 100°C (212°F). |
| • | When A/C is requested and the ambient temperature is more than 10°C (50°F). |
| • | A/C refrigerant pressure exceeds 1310 kPa (190 psi). |
| • | After the vehicle is shut off if the engine coolant temperature at key-off is more than 117°C (243°F) and system voltage is more than 12 volts. The fans will stay on for approximately 4 minutes. |
The BCM will request high speed cooling fan operation from the PCM under the following conditions:
| • | Engine coolant temperature reaches 105°C (221°F). |
| • | A/C refrigerant pressure exceeds 1655 kPa (240 psi). |
| • | When certain DTCs set. |
Engine Coolant Indicator(s)
TEMP
| • | The IPC illuminates the TEMP indicator when the PCM determines that the coolant temperature is greater than 128°C (262°F). The IPC receives a discrete input from the PCM requesting illumination. |
| • | The IPC performs the displays test at the start of each ignition cycle. The IPC illuminates the TEMP indicator. |
Coolant Heater
The optional engine coolant heater (RPO K05) operates using 110-volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather -29°C (-20°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.
Cooling System
The cooling system's 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.
Cooling Cycle
Coolant flows from the radiator outlet and into the water pump inlet. Some coolant flows from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost capability as the coolant warms up.
Coolant also flows from the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where the coolant absorbs heat.
The coolant then flows through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where the coolant absorbs additional heat.
Coolant is also directed to the throttle body. There the coolant circulates through passages in the casting. During initial warm-up, the coolant assists in warming the throttle body.
From the cylinder heads, the coolant flows to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine reaches normal operating temperature, or the coolant will flow through the thermostat and into the radiator where the coolant is cooled. At this point, the coolant flow cycle is completed.
Efficient operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components.
Coolant
The engine coolant is a solution made up of a 50/50 mixture of DEX-COOL and suitable drinking water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.
Radiator
The radiator is a heat exchanger consisting of a core and 2 tanks. The aluminum core is a tube and fin crossflow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere.
The inlet and outlet tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the tank flange edge to the aluminum core. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.
The radiator also has a drain cock located in the bottom of the left hand tank. The drain cock unit includes the drain cock and drain cock seal.
Heat is removed from the coolant as the coolant passes through the radiator. The fins on the core transfer heat from the coolant passing through the tubes. Air passing between the fins absorbs the heat and cools the coolant.
Pressure Cap
The pressure cap seals and pressurizes the cooling system. The cap contains a blow off, or pressure valve and a vacuum, or an atmospheric valve:
| • | The pressure valve is held against the seat by a spring that protects the radiator by relieving pressure that exceeds 15 psi. |
| • | The vacuum valve is held against the seat by a spring that permits opening of the valve to relieve vacuum created when the cooling system cools. The vacuum, if not relieved, might cause the radiator to collapse. |
The pressure cap allows the cooling system pressure to build up when the temperature increases. As the pressure builds, the boiling point of the coolant increases. Therefore, the engine coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant becomes, the faster the heat transfers from the radiator into the cooler air.
The pressure in the cooling system can get too high. When the pressure exceeds the strength of the spring, the pressure valve rises, venting the excess pressure.
As the engine cools, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open. This equalizes the pressure in the cooling system with the atmospheric pressure, preventing the radiator from collapsing.
Coolant Recovery System
The coolant recovery system consists of a plastic coolant recovery reservoir and overflow tube. The recovery reservoir is also called a recovery tank or expansion tank. This tank is partially filled with coolant and is connected to the radiator fill neck with the overflow tube. Coolant can flow back and forth between the radiator and the reservoir.
In effect, a cooling system with a coolant recovery reservoir is a closed system. When the pressure within the cooling system gets too high, the pressure valve in the pressure cap will open. This allows the coolant, which has expanded due to heat, to flow through the overflow tube and into the recovery reservoir. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum opens the vacuum valve in the pressure cap, allowing some of the coolant in the reservoir to be siphoned back into the radiator. Under normal operating conditions, no coolant is lost. Although the coolant level in the recovery reservoir goes up and down, the radiator and cooling system are kept full. An advantage to using a coolant recovery reservoir is the elimination of almost all air bubbles from the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.
Air Baffles and Seals
The cooling system uses deflectors, air baffles and air seals to increase cooling system capability. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle and through the radiator to increase engine cooling. Air baffles are also used to direct airflow through the radiator and increase cooling capability. Air seals prevent air from bypassing the radiator and A/C condenser, and prevent recirculation of hot air for better hot weather cooling and A/C condenser performance.
Water Pump
The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages and an impeller. The impeller is a flat plate mounted on the pump shaft with a series of flat or curved blades or vanes. When the impeller rotates, the coolant between the vanes is thrown outward by centrifugal force. The impeller shaft is supported by one or more sealed bearings. These sealed bearings never need to be lubricated. With a sealed bearing, grease cannot leak out, and dirt and water cannot get in.
The purpose of the water pump is to circulate coolant throughout the cooling system. The water pump is driven by the crankshaft via the drive belt.
Thermostat
The thermostat is a coolant flow control component. It's purpose is to regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a piston. When the element is heated, it expands and exerts pressure against a rubber diaphragm. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.
When the coolant temperature is below 91°C (195°F), the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 91°C (195°F), the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, even after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.
Engine Oil Cooler
The engine oil cooler is a heat exchanger which is located external to the radiator. The oil temperature is cooled by the air passing through the oil cooler fins. The oil pump pumps the oil through the feed line to the oil cooler. The oil flows through the cooler where the air absorbs heat from the oil. The oil is then pumped through the cooler return line to the oil filter and returns to the main oil passage.
Transmission Oil Cooler - Internal
The transmission oil cooler is a heat exchanger that is located inside one of the radiator end tanks. The transmission fluid temperature is regulated by the temperature of the engine coolant in the radiator. The oil pump pumps the fluid through the transmission oil cooler feed line to the oil cooler. The fluid flows through the cooler where the engine coolant absorbs heat from the fluid. The fluid is then pumped through the oil cooler return line back to the transmission.
Transmission Oil Cooler - External
The transmission oil cooler is a heat exchanger that is located external to the radiator. Air passing through the oil cooler fins cools the transmission fluid temperature. Within the transmission system, the oil pump pumps the fluid through the feed line to the oil cooler. The fluid then flows through the cooler where air absorbs heat from the fluid. The fluid is then pumped through the oil cooler return line back to the transmission.
