Intermittent
Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Cooling Fan Always On
| Symptom | Causes |
|---|---|
| Both fan motors always on. | Short to ground in the fan 1 relay coil control circuit Short to ground in the fan motor low speed ground circuit Fan relay 1 internal contacts shorted together. |
| One fan motor always on. | Short to ground in the fan 2 relay coil control circuit Short to ground in the fan motor ground circuit Fan relay 2 internal contacts shorted together. |
Reference Table
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views DEFINITION: The cooling fan motors are always on in low speed. | |||
| 1 | Did you review the Cooling System Description and Operation and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Cooling |
| 2 | With the engine OFF. Is one or both the fan motors running continuously? | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems |
| 3 | Are both fan motors on? | Go to Step 7 | Go to Step 4 |
| 4 | Remove the fan 2 relay from the underhood fuse block. Is the fan motor running continuously? | Go to Step 6 | Go to Step 5 |
| 5 | Test the fan 2 relay coil control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 11 |
| 6 | Repair the short to ground in the fan motor ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | |
| 7 | Remove the fan 1 relay from the underhood fuse block. Are the fan motors running continuously? | Go to Step 8 | Go to Step 9 |
| 8 | Repair the short to ground in the fan motor ground circuit between the fan motors and the fan 1 relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | |
| 9 | Test the fan 1 relay coil control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 10 |
| 10 | Replace the fan 1 relay. Refer to Cooling Fan Relay Replacement . Did you complete the replacement? | Go to Step 12 | |
| 11 | Replace the fan 2 relay. Refer to Cooling Fan Relay Replacement . Did you complete the replacement? | Go to Step 12 | |
| 12 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
Cooling Fan Always On
Cooling Fan Inoperative
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views DEFINITION: One or both engine cooling fan motors do not operate properly in high or low speed modes. | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the Fans Low Speed ON and OFF. Do the low speed engine cooling fans turn ON and OFF with each command? | Go to Step 3 | Go to Step 4 |
| 3 | IMPORTANT: A 3-second delay occurs before the powertrain control module (PCM) changes the cooling fan speed. With a scan tool, command the Fans High Speed ON and OFF.Do the high speed engine cooling fans turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 12 |
| 4 | IMPORTANT: Do NOT remove the 20-amp fused jumper wire connected during this step. Use a second 20-amp fused jumper wire while performing the following steps. Remove the fan 1 relay. Connect a 20-amp fused jumper between the battery positive switch side voltage circuit and the fan motor supply voltage circuit of the cooling fan 1 relay. Do both cooling fans operate in low speed? | Go to Step 22 | Go to Step 5 |
| 5 | Disconnect the fan 2 relay. Connect the second 20-amp fused jumper between the cooling fan low reference circuit and the cooling fan motor supply voltage circuit of the fan 2 relay. Do both cooling fans operate in low speed? | Go to Step 23 | Go to Step 6 |
| 6 | Connect the second 20-amp fused jumper between the battery positive voltage circuit and the cooling fan motor supply voltage circuit of the fan 2 relay. Does the right cooling fan operate in high speed? | Go to Step 9 | Go to Step 7 |
| 7 | Install the fan 2 relay. Disconnect the right cooling fan electrical connector. Connect the second 20-amp fused jumper wire from the cooling fan motor supply voltage circuit to the ground circuit of the right cooling fan electrical connector. Does the left cooling fan operate in high speed? | Go to Step 25 | Go to Step 8 |
| 8 | Connect the second 20-amp fused jumper wire from the cooling fan motor supply voltage circuit of the right cooling fan electrical connector to a good ground. Does the left cooling fan operate in high speed? | Go to Step 29 | Go to Step 30 |
| 9 | Install the fan 2 relay. Disconnect the left cooling fan electrical connector. Connect the second 20-amp fused jumper wire from the cooling fan motor supply voltage circuit to the cooling fan low reference circuit of the left cooling fan electrical connector. Does the right cooling fan operate in high speed? | Go to Step 26 | Go to Step 10 |
| 10 | Connect the second 20-amp fused jumper wire from the coil side battery positive voltage circuit to the cooling fan low reference circuit of the cooling fan electrical connector. Does the right cooling fan operate in high speed? | Go to Step 11 | Go to Step 31 |
| 11 | Probe the battery positive voltage circuit on the switch side of the fan 1 relay with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 27 | Go to Step 32 |
| 12 | Is the right cooling fan operating properly in high speed? | Go to Step 19 | Go to Step 13 |
| 13 | Turn OFF the ignition. Disconnect the fan 3 relay. Turn ON the ignition, with the engine OFF. Connect a test lamp between the high speed cooling fan relay control circuit and the battery positive voltage circuit on the coil side of the fan 3 relay. With a scan tool command the High Speed Fans ON and OFF. Does the test lamp turn ON and OFF with each command? | Go to Step 15 | Go to Step 14 |
| 14 | Probe the battery positive voltage circuit on the coil side of the fan 3 relay with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 34 | Go to Step 33 |
| 15 | Install a 20-amp fused jumper between the battery positive voltage circuit on the switch side of the fan 3 relay and the cooling fan motor supply voltage circuit. Does the right cooling fan operate in high speed? | Go to Step 24 | Go to Step 16 |
| 16 | Probe the battery positive voltage circuit on the switch side of the fan 3 relay with a test lamp connected to a good ground. Does the test lamp illuminate? | Go to Step 17 | Go to Step 33 |
| 17 | With the 20-amp fused jumper still installed. Disconnect the right cooling fan electrical connector. Connect a test lamp from the cooling fan motor supply voltage circuit to the ground circuit of the right cooling fan electrical connector. Does the test lamp illuminate? | Go to Step 25 | Go to Step 18 |
| 18 | Probe the cooling fan motor supply voltage circuit of the right cooling fan electrical connector with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 29 | Go to Step 30 |
| 19 | Turn OFF the ignition. Disconnect the fan 2 relay. Turn ON the ignition, with the engine OFF. Connect a 20-amp fused jumper between the cooling fan low reference circuit and the ground circuit of the fan 2 relay. With a scan tool command the Fans High Speed ON and OFF. Does the left cooling fan operate in high speed? | Go to Step 20 | Go to Step 28 |
| 20 | Connect a test lamp between the high speed cooling fan relay control circuit of the fan 2 relay and the battery positive voltage circuit of the fan 2 relay. With a scan tool command the Fans High Speed ON and OFF. Does the test lamp turn ON and OFF with each command? | Go to Step 23 | Go to Step 21 |
| 21 | Probe the battery positive voltage circuit of the fan 2 relay with a test lamp that is connected to a good ground. Does the test lamp illuminate? | Go to Step 34 | Go to Step 33 |
| 22 | Inspect for poor connections at the fan 1 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 40 | Go to Step 35 |
| 23 | Inspect for poor connections at the fan 2 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 40 | Go to Step 36 |
| 24 | Inspect for poor connections at the fan 3 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 40 | Go to Step 37 |
| 25 | Inspect for poor connections at the harness connector of the right cooling fan. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 40 | Go to Step 38 |
| 26 | Inspect for poor connections at the harness connector of the left cooling fan. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 40 | Go to Step 39 |
| 27 | Repair the left cooling fan motor supply voltage circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | Go to Step 40 | |
| 28 | Repair the left cooling fan ground circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | Go to Step 40 | |
| 29 | Repair the right cooling fan ground circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | Go to Step 40 | |
| 30 | Repair the right cooling fan motor supply voltage circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | Go to Step 40 | |
| 31 | Repair the left cooling fan low reference circuit for a short to ground or an open. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | Go to Step 40 | |
| 32 | Repair the fan 1 relay battery positive voltage circuit for an open. Is the repair complete? | Go to Step 40 | |
| 33 | Repair the battery positive voltage circuit for the fan 2 relay and fan 3 relay for an open. Is the repair complete? | Go to Step 40 | |
| 34 | Repair the high speed cooling fan relay control circuit for an open. Is the repair complete? | Go to Step 40 | |
| 35 | Replace the fan 1 relay. Is the repair complete? | Go to Step 40 | |
| 36 | Replace the fan 2 relay. Is the repair complete? | Go to Step 40 | |
| 37 | Replace the fan 3 relay. Is the repair complete? | Go to Step 40 | |
| 38 | Replace the right cooling fan. Refer to Cooling Fan Motor Replacement - Electric . Is the repair complete? | Go to Step 40 | |
| 39 | Replace the left cooling fan. Refer to Cooling Fan Motor Replacement - Electric . Is the repair complete? | Go to Step 40 | |
| 40 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
| IMPORTANT |
|---|
| A 3-second delay occurs before the powertrain control module (PCM) changes the cooling fan speed. |
| IMPORTANT |
|---|
| Do NOT remove the 20-amp fused jumper wire connected during this step. Use a second 20-amp fused jumper wire while performing the following steps. |
Cooling Fan Inoperative
Engine Overheating
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Inspect the following: The level of the coolant The mixture of the coolant Is the coolant mixed properly and at the proper level? | Go to Step 3 | Go to Step 2 |
| 2 | Add the coolant. Does the engine still overheat? | Go to Step 3 | System OK |
| 3 | Inspect the generator/coolant pump drive belt. Is the generator/coolant pump drive belt loose or missing? | Go to Step 4 | Go to Step 5 |
| 4 | Adjust or replace the belt. Does the engine still overheat? | Go to Step 5 | System OK |
| 5 | Inspect the front of the radiator for the following items: Dirt Leaves Insects Is the front of the radiator dirty? | Go to Step 6 | Go to Step 7 |
| 6 | Clean the front of the radiator. Does the engine still overheat? | Go to Step 7 | System OK |
| 7 | Inspect the following components for leaks: The hoses The coolant pump The heater The thermostat housing The radiator The head gasket Is leakage present? | Go to Step 8 | Go to Step 9 |
| 8 | Repair the leaks as necessary. Does the engine still overheat? | Go to Step 9 | System OK |
| 9 | Inspect the thermostat. Is the thermostat faulty? | Go to Step 10 | Go to Step 11 |
| 10 | Replace the thermostat. Does the engine still overheat? | Go to Step 11 | System OK |
| 11 | Inspect the cylinder head torque. Is the cylinder head torque correct? | Go to Step 13 | Go to Step 12 |
| 12 | Re-tighten the cylinder head bolts to specification. Replace the cylinder head gasket if required. Does the engine still overheat? | Go to Step 13 | System OK |
| 13 | Inspect the intake manifold. Is the intake manifold leaking? | Go to Step 14 | Go to Step 15 |
| 14 | Complete the following actions as necessary in order to correct the leak: Repair the intake manifold. Replace the components. Does the engine still overheat? | Go to Step 15 | System OK |
| 15 | Inspect the cylinder head gasket. Is the cylinder head gasket leaking? | Go to Step 16 | Go to Step 17 |
| 16 | Repair or replace the components as necessary in order to correct the leak. Does the engine still overheat? | Go to Step 17 | System OK |
| 17 | Inspect the cylinder block plug. Is the cylinder block plug leaking? | Go to Step 18 | Go to Step 19 |
| 18 | Repair or replace the components as necessary in order to correct the leak. Does the engine still overheat? | Go to Step 19 | System OK |
| 19 | Inspect the heater core. Is the heater core leaking? | Go to Step 20 | Go to Step 21 |
| 20 | Repair or replace the components as necessary in order to correct the leak. Does the engine still overheat? | Go to Step 21 | System OK |
| 21 | Inspect the coolant valve, if equipped. Is the coolant valve leaking? | Go to Step 22 | |
| 22 | Repair or replace the components as necessary in order to correct the leak. Does the engine still overheat? | System OK |
Engine Overheating
Loss of Coolant
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Inspect the radiator. Is the radiator leaking? | Go to Step 2 | Go to Step 3 |
| 2 | Repair the radiator as necessary. Is a loss of coolant still evident? | Go to Step 3 | System OK |
| 3 | Inspect the surge tank cap. Is the surge tank cap faulty? | Go to Step 4 | Go to Step 5 |
| 4 | Perform a surge tank cap pressure test. Replace the cap if necessary. Is a loss of coolant still evident? | Go to Step 5 | System OK |
| 5 | Inspect the following components: The coolant surge tank The hoses Is the surge tank or the hoses leaking? | Go to Step 6 | Go to Step 7 |
| 6 | Replace the surge tank or the hoses. Is a loss of coolant still evident? | Go to Step 7 | System OK |
| 7 | Inspect the following components: The radiator The heater hoses The connections Is any damage evident? | Go to Step 8 | Go to Step 9 |
| 8 | Repair or replace the components as necessary in order to correct the leak. Is a loss of coolant still evident? | Go to Step 9 | System OK |
| 9 | Inspect the water pump seal. Is the water pump seal leaking? | Go to Step 10 | Go to Step 11 |
| 10 | Replace the water pump. Is a loss of coolant still evident? | Go to Step 11 | System OK |
| 11 | Inspect the water pump sealing surface. Is the water pump O-Ring or gaskets leaking? | Go to Step 12 | Go to Step 13 |
| 12 | Replace the O-Ring or gaskets. Is a loss of coolant still evident? | System OK | |
| 13 | Inspect the cylinder block, cylinder head and gasket surface. Is the cylinder block, cylinder head or gasket leaking? | Go to Step 14 | System OK |
| 14 | Repair or replace the components as necessary in order to correct the leak. Is a loss of coolant still evident? | System OK |
Loss of Coolant
Engine Fails To Reach Normal Operating Temperature
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Inspect the thermostat for the following conditions: The thermostat remains open. An incorrect thermostat is installed. Does either of the above conditions exist? | Go to Step 2 | Go to Step 3 |
| 2 | Install a new thermostat of the correct type and heat range. Does the engine still fail to reach the normal operating temperature? | Go to Step 3 | System OK |
| 3 | Inspect the coolant level. Is the coolant level below the ADD mark? | Go to Step 4 | Go to Step 5 |
| 4 | Add coolant. Does the engine still fail to reach the normal operating temperature? | Go to Step 5 | System OK |
| 5 | Inspect the radiator for the following conditions: Plugging A faulty cap Does either of the above conditions exist? | Go to Step 6 | Go to Step 7 |
| 6 | Inspect the radiator or the cap. Replace the cap as necessary. Does the engine reach the normal operating temperature? | System OK | Go to Step 7 |
| 7 | Inspect the cylinder head. Is the cylinder head or block cracked or plugged? | Go to Step 8 | |
| 8 | Repair the cylinder head or block as necessary. Does the engine reach the normal operating temperature? | System OK |
Engine Fails To Reach Normal Operating Temperature
Filling Procedure
- Install the radiator drain cock.
- Lower the vehicle.
- Slowly fill the cooling system through the upper radiator hose with a 50/50 coolant mixture until the coolant comes out the coolant air bleed hose.
- Fill the radiator with coolant through the surge tank opening to the full line.
- Install the radiator cap.
- Start the engine.
- Run the engine at 2,000-2,500 RPM until the engine reaches normal operating temperature.
- Allow the engine to idle for 3 minutes.
- Shut the engine OFF.
- Allow the engine to cool.
- Top off the coolant as necessary.
- Inspect the concentration of the engine coolant.
- Rinse away any excess coolant from the engine and the engine compartment.
- Inspect the cooling system for leaks.
Cooling Cycle
Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Some coolant will then be pumped from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.
Coolant is also pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.
The coolant is then forced 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 it absorbs additional heat.
Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start-up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in keeping the throttle body cool.
From the cylinder heads, the coolant is then forced to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or it will flow through the thermostat and into the radiator where it is cooled and the coolant cycle is completed.
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 clean drinkable 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. It consists of a core and 2 tanks. The aluminum core is a crossflow tube and fin design. This is a series of tubes that extend side to side from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer from the coolant to the atmosphere. The inlet and outlet tanks are molded with a high temperature, nylon reinforced plastic. A high temperature rubber gasket seals the tank flange edge. 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 removes heat from the coolant passing through it. The fins on the core absorb heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.
During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.
Screw On Pressure Cap
The pressure cap is a cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of predetermined strength, which protects the radiator by relieving pressure if it exceeds 15 psi. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator to collapse.
The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat moves from the radiator to the cooler, passing air. The pressure in the cooling system can get too high. However, when the pressure exceeds the strength of the spring, it raises the pressure valve so that the excess pressure can escape. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the cooling system. This equalizes the pressure in the cooling system with 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 provides an air space in the cooling system that allows the coolant to expand and contract. The surge tank provides a coolant fill point and a central air bleed location. It 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 in the cooling system gets too high, it will open the pressure valve in the pressure cap. This allows the coolant, which has expanded due to being heated, 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.
During vehicle use, the coolant heats and expands. The increased coolant volume flows into the recovery reservoir. As the coolant circulates, any air is allowed to bubble out. Coolant without air bubbles absorbs heat much better than coolant with bubbles.
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 86°C (186°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 86°C (186°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.
Transmission Oil Cooler
The transmission oil cooler is a heat exchanger. It is located inside the left side end tank of the radiator. The transmission fluid temperature is regulated by the temperature of the engine coolant that surrounds the oil cooler as the transmission fluid passes down through the cooler.
The transmission oil pump pumps the fluid through the transmission oil cooler feed line to the oil cooler. The fluid then flows down through the cooler while the engine coolant absorbs heat from the fluid. The fluid is then pumped through the transmission oil cooler return line to the transmission.
Stage One - Both Fans Operate at Low Speed
The ECM determines when the engine cooling fans should operate at Stage 1 (engine cooling fan relay 1 is energized and both fans, being connected in series, run at low speed) based on inputs from the A/C request signal, VSS and the ECT sensor. When the conditions for Stage 1 operation are met the ECM provides a ground to the coil of engine cooling fan relay 1, causing it to operate (turn ON); the fan current path is then from the battery via the large radiator fan fuse, through the large fan motor, cooling fan relay 2, the small fan motor and cooling fan relay 1 to ground.
The conditions for Stage 1 operation are
- There is an A/C request and: Vehicle speed is less than 30 km/h (19 mph) or; A/C refrigerant pressure is greater than 1500 kPa (218 psi) or
- ECT is greater than 98°C (208°F) or
- ECT is greater than 113°C (235°F) when the engine is switched off (in this case stage 1 will operate for approximately four minutes - this is referred to as low fan run-on) or
- An ECT sensor fault is detected and a DTC such as P0117, P0118, P1114 or P1115 is set.
Stage 1 operation will cease when
- There is no A/C request and the engine coolant temperature is less than 95°C (203°F) or
- There is an A/C request and the vehicle speed is greater than 50 km/h (31 mph) and the A/C pressure is less than 1170 kPa (170 psi) and the ECT is less than 95°C (203°F) or
- The vehicle speed is greater than 104 km/h (65 mph).
Stage Two - Both Fans Operate at High Speed
The ECM also determines when the engine cooling fans should operate at Stage 2 (that is, engine cooling fan relays 1, 2 and 3 are energized and both fans, each being connected to battery voltage, run at high speed) based on inputs from the A/C request signal, VSS and the ECT sensor. When the conditions for Stage 2 operation are met the ECM provides - in addition to that already provided for the coil of engine cooling fan relay 1 - a ground to the coils of engine cooling fan relays 2 and 3, causing them to operate (turn ON). For the large fan the current path is then from the battery via the large radiator fan fuse, through the large fan motor and engine cooling fan relay 2 to ground. For the small fan the current path is from the battery via the small radiator fan fuse, through engine cooling fan relay 3, through the small fan motor and engine cooling fan relay 1 to ground. The conditions for Stage 2 operation are
- The A/C refrigerant pressure is greater than 2400 kPa (348 psi) or
- The ECT is greater than 108°C (226°F) or
- An ECT sensor fault is detected and a DTC such as P0117, P0118, P1114 or P1115 is set.
- There is a body control module (BCM) message response fault, which will cause a powertrain interface module (PIM) DTC B2002 to set.
If stage 1 operation is off when the conditions for stage 2 operation are met, stage 2 operation will be initiated five seconds after initiation of Stage 1 operation.
Stage 2 operation will cease and revert to Stage 1 operation when
- The engine coolant temperature is less than 102°C (216°F) and; There is no A/C request or; There is an A/C request and the A/C refrigerant pressure is less than 1900 kPa (276 psi) or
- The vehicle speed is greater than 104 km/h (65 mph).