Q: How to replace the electric fan in a Nissan Quest?
A: All models have a two-speed electric fan mounted in a plastic shroud attached to the back of the Radiator. Fan operation is controlled both by the PCM and the high and low-speed fan relays. The Coolant Temperature Sensor signals the PCM of engine temperature, and the PCM turns on the appropriate relay(s). At warm idle, the low-speed relay turns the fan on at low speed. When the coolant temperature reaches 221 degrees F, the PCM turns the high-speed relays 1 and 2 on, causing the fan to run at high speed. There are two high-speed relays to ensure proper cooling even if one relay fails, and they will also operate if the coolant temperature sensor fails. If the fan operates continuously, the fault could be the coolant temperature sensor or the relays. Warm the engine up until the gauge on the instrument panel indicates the high side of NORMAL. The fan should come on. If not, check the RAD FAN fuse in the center engine compartment fuse panel and the ALY COIL fuse in the interior fuse panel. If the fuses checked OK, disconnect the electrical connector from the radiator fan motor. Attach a fused jumper wire with battery voltage to either of the two power terminals on the fan, and a chassis-ground jumper to the black wire terminal on the fan. If the fan doesn't operate, it should be replaced. If it does operate with jumper wires, but doesn't under normal driving conditions, connect a voltmeter to a chassis ground and probe the power terminals of the fan connector on the harness side. If the engine is hot and the temperature gauge shows above NORMAL, there should be battery voltage at one of these terminals. Check the ground of the circuit by switching your meter to the ohms scale. Ground one side of the meter and probe the other side at the black wire terminal of the fan connector. Resistance should be no more than 5 ohms. If resistance is high, trace the ground wire circuit to the chassis. If there had been no power at the terminals, check that power is being supplied to the low-speed fan relay. One of its sockets on the relay panel should exhibit battery voltage at all times, and one only when the key is in the On or Start position. Replacement: Disconnect the electrical connector from the fan motor. Disconnect the upper radiator hose and overflow hose at the radiator. Remove the two fan shroud bolts and remove the fan/shroud assembly. Note: The bottom of the fan shroud fits into tabs on the radiator. Remove the small clip retaining the fan to the motor shaft. Remove the screws retaining the motor to the shroud. With an assistant retaining the fan, hit the shaft of the motor with a hammer and blunt punch to separate the fan from the motor. Installation is the reverse of removal.