Cooling Fan Description and Operation (LHU/A20NFT, LAU/A28NER)
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Cooling Fan Description and Operation (LHU/A20NFT, LAU/A28NER)
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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.
