Overview
The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each 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 cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
Low Speed Operation
The ECM provides a ground at the control circuit, for the coil side of the KR20C and KR20D relays. The KR20C Cooling Fan Low Speed Relay activates and supplies voltage through the switch side of the relay, directly to terminal 1 of the left cooling fan. The left cooling fan is connected in series to terminal 2 of the right cooling fan, via the de-energized KR20L Cooling Fan Speed Control 2 Relay. Both fans operate at a low speed as a result of the series circuit through the internal resistor of the right engine cooling fan. The KR20D relay remains inactive because ignition voltage to the KR20D relay coil is supplied by the KR20E relay, which is controlled by the KR20F relay.
Medium Speed Operation
The ECM provides a ground for the coil side of the KR20F Cooling Fan Relay. The energized KR20F relay completes a ground, through the switch side of the relay, for the coils of the KR20E, KR20M, KR20L and KR20N relays. The KR20E Cooling Fan Speed Control Relay activates and supplies ignition voltage to the coil side of the KR20D Cooling Fan High Speed Relay. The KR20D relay remains inactive because the ECM is not commanding the KR20D relay control circuit ON. The KR20M Cooling Fan-Left Medium Speed Relay activates and provides B+ to the left cooling fan through cooling fan terminal 2 and the internal resistor. The KR20N Cooling Fan-Right Medium Speed Relay activates and provides B+ to the right cooling fan, through cooling fan terminal 2 and the internal resistor. The KR20L Cooling Fan Speed Control 2 Relay also activates and provides a dedicated ground for the left cooling fan. The result is both cooling fans operating at a reduced speed through their individual resistor and ground circuits.
High Speed Operation
The ECM provides a ground at both cooling fan relay control circuits. The KR20C Cooling Fan Low Speed Relay activates and provides B+ directly to the left cooling fan through cooling fan terminal 1. The KR20D Cooling Fan High Speed Relay activates and provides B+ directly to the right cooling fan through cooling fan terminal 1. The KR20L Cooling Fan Speed Control 2 Relay also activates and provides a direct ground for the left cooling fan. The result is both cooling fans operating at full speed.
Circuit/System Description
The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each 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 cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
Description and Operation
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine control module (ECM) commands the fan ON in either high speed, medium speed, or low speed, depending on cooling requirements. In low speed, the fan is turned ON at a reduced speed. In medium speed, the fan is turned ON at a higher reduced speed. In high speed, the fan is turned ON at full speed.
In low speed operation, the ECM provides ground from ECM terminal X2 14 to the cooling fan relay. The cooling fan relay activates and provides ground to the coils of the cooling fan medium speed 2 relay and the cooling fan speed control relay. The cooling fan speed control relay activates and provides power to the coil of the cooling fan high speed relay. The cooling fan high speed relay remains inactive because ECM terminal X2 12 is not grounded. The cooling fan medium speed 2 relay provides power to the cooling fan motor through cooling fan terminal 2 and the internal fan resistor.
In medium speed operation, the ECM provides ground from ECM terminal X2 12 to the cooling fan high speed relay and the cooling fan medium speed 1 relay. The cooling fan high speed relay remains inactive because power is not provided to the coil from the cooling fan speed control relay. The cooling fan medium speed 1 relay activates and provides power to the cooling fan motor through cooling fan terminal 3 and the internal fan resistor.
In high speed operation, the ECM provides ground from ECM terminals X2 12 and X2 14. As previously described, power is now provided to both cooling fan terminals 2 and 3. In addition, power and ground are now provided to the coil of the cooling fan high speed relay. The cooling fan high speed relay activates and provides power to the cooling fan motor through cooling fan terminal 4, bypassing the internal fan resistors.
COOLING SYSTEM DESCRIPTION AND OPERATION
The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each 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 cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine control module (ECM) commands the fan ON in either high speed, medium speed, or low speed, depending on cooling requirements. In low speed, the fan is turned ON at a reduced speed. In medium speed, the fans are turned ON at a higher reduced speed. In high speed, the fans are turned ON at full speed. In low speed operation, the ECM provides ground to ECM terminal 94 X2. The cooling fan relay activates and provides ground to the coil of the cooling fan left high speed relay. The cooling fan speed control relay remains inactive because ECM terminal 90 X2 is not grounded. The cooling fan left high speed relay provides power to the engine cooling fan right through engine cooling fan left and the internal fan resistor of engine cooling fan right.
In medium speed operation, the ECM provides ground to ECM terminal 90 X2. The cooling fan left low speed, cooling fan speed control relay and the cooling fan right low speed relay are activated. The internal fan resistor of the engine cooling fan left is provided with power through the cooling fan left low speed relay. The cooling fan speed control relay is active and therefore the engine cooling fan left terminal 3 is directly shorted to ground. The cooling fan right low speed relay is active and provides power to the internal resistor of the engine cooling fan right. The engine cooling fan right terminal 3 is directly shorted to ground. Both fans runs with medium speed.
In high speed operation, the ECM provides ground to ECM terminals 90 X2, 91 X2 and 94 X2. Cooling fan left high speed relay, cooling fan medium speed 1 relay, cooling fan left low speed relay, cooling fan speed control relay and cooling fan right low speed relay are activated. Power is now provided to both cooling fan terminals 1. The engine cooling fan relay left is directly shorted to ground through the cooling fan speed control relay. The engine cooling fan right is directly shorted to ground. In this constellation both fans run without resistor.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine control module (ECM) commands the fan ON in either high speed, medium speed, or low speed, depending on cooling requirements. In low speed, the fan is turned ON at a reduced speed. In medium speed, the fans are turned ON at a higher reduced speed. In high speed, the fans are turned ON at full speed. In low speed operation, the ECM provides ground to ECM terminal 94 X2. The cooling fan relay activates and provides ground to the coil of the cooling fan left high speed relay. The cooling fan speed control relay remains inactive because ECM terminal 90 X2 is not grounded. The cooling fan left high speed relay provides power to the engine cooling fan right through engine cooling fan left and the internal fan resistor of engine cooling fan right.
In medium speed operation, the ECM provides ground to ECM terminal 90 X2. The cooling fan left low speed, cooling fan speed control relay and the cooling fan right low speed relay are activated. The internal fan resistor of the engine cooling fan left is provided with power through the cooling fan left low speed relay. The cooling fan speed control relay is active and therefore the engine cooling fan left terminal 3 is directly shorted to ground. The cooling fan right low speed relay is active and provides power to the internal resistor of the engine cooling fan right. The engine cooling fan right terminal 3 is directly shorted to ground. Both fans runs with medium speed.
In high speed operation, the ECM provides ground to ECM terminals 90 X2, 91 X2 and 94 X2. Cooling fan left high speed relay, cooling fan medium speed 1 relay, cooling fan left low speed relay, cooling fan speed control relay and cooling fan right low speed relay are activated. Power is now provided to both cooling fan terminals 1. The engine cooling fan relay left is directly shorted to ground through the cooling fan speed control relay. The engine cooling fan right is directly shorted to ground. In this constellation both fans run without resistor.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine cooling system contains an engine coolant level switch to alert the driver in the event of a low coolant level. The coolant level switch is mounted at the lowest point in the cooling system surge tank. If the amount engine coolant in the surge tank drops below the level of the switch, the coolant level switch opens. If the engine coolant level is low or the switch is open for greater than 10 seconds, the IPC will turn ON the Low Coolant Indicator lamp. The lamp will also illuminate for approximately 3 seconds during the display test at the start of each ignition cycle.
COOLING SYSTEM DESCRIPTION AND OPERATION
The engine control module (ECM) commands the fans ON in either high speed, medium speed, or low speed, depending on cooling requirements.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each 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 cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine cooling fan system is composed of one fan, 5 relays, the engine control module (ECM), and the associated wiring. The fan assembly includes two resistors, which enable the fan to operate at 3 speeds.
In low speed operation, the ECM provides ground from ECM terminal X2 44. The Cooling Fan Relay activates and provides ground to the coils of the Cooling Fan Medium Speed 2 Relay and the Cooling Fan Speed Control Relay. The Cooling Fan Speed Control Relay activates and provides power to the coil of the Cooling Fan High Speed Relay. The cooling fan high speed relay remains inactive because ECM terminal X2 12 is not grounded. The Cooling Fan Medium Speed 2 Relay provides power to the cooling fan motor through cooling fan terminal 2 and the internal fan resistor.
In medium speed operation, the ECM provides ground to ECM terminal X2 12. The Cooling Fan High Speed Relay remains inactive because power is not provided to the coil from the Cooling Fan Speed Control Relay. The Cooling Fan Medium Speed 1 Relay activates and provides power to the cooling fan motor through cooling fan terminal 3 and the internal fan resistor.
In high speed operation, the ECM provides ground to ECM terminals X2 12 and X2 44. As previously described, power is now provided to both cooling fan terminals 2 and 3. In addition, power and ground are now provided to the coil of the Cooling Fan High Speed Relay. The Cooling Fan High Speed Relay activates and provides power to the cooling fan motor through cooling fan terminal 4.
COOLING SYSTEM DESCRIPTION AND OPERATION
The engine control module (ECM) commands the fans ON in either high speed, medium speed, or low speed, depending on cooling requirements.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each 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 cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine control module (ECM) commands the fans ON in either high speed, medium speed, or low speed, depending on cooling requirements.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine control module (ECM) commands the fans ON in either high speed, medium speed, or low speed, depending on cooling requirements.
COOLING FAN DESCRIPTION AND OPERATION (LHU/A20NFT, LAU/A28NER)
The engine cooling fan system is composed of one fan, 5 relays, the engine control module (ECM), and the associated wiring. The fan assembly includes two resistors, which enable the fan to operate at 3 speeds.
In low speed operation, the ECM provides ground from ECM terminal X2 44 (LDE/2H0), or terminal X2 14 (LLU). The cooling fan relay activates and provides ground to the coils of the cooling fan medium speed 2 relay and the cooling fan speed control relay. The cooling fan speed control relay activates and provides power to the coil of the cooling fan high speed relay. The cooling fan high speed relay remains inactive because ECM terminal X2 15 (LDE/2H0) or terminal X2 12 (LLU) is not grounded. The cooling fan medium speed 2 relay provides power to the cooling fan motor through cooling fan terminal 2 and the internal fan resistor.
In medium speed operation, the ECM provides ground to ECM terminal X2 15 (LDE/2H0) or terminal X2 12 (LLU). The cooling fan high speed relay remains inactive because power is not provided to the coil from the cooling fan speed control relay. The cooling fan medium speed 1 relay activates and provides power to the cooling fan motor through cooling fan terminal 3 and the internal fan resistor.
In high speed operation, the ECM provides ground to ECM terminals X2 15 and X2 44 (LDE/2H0) or terminals X2 12 and X2 14 (LLU). As previously described, power is now provided to both cooling fan terminals 2 and 3. In addition, power and ground are now provided to the coil of the cooling fan high speed relay. The Cooling Fan High Speed Relay activates and provides power to the cooling fan motor through cooling fan terminal 4.
COOLING SYSTEM DESCRIPTION AND OPERATION