Question about 1993 Toyota Corolla
You must have a problem in the fan circuit, either the fuse, the relay, power to the relay, or the sensor.
Easiest place to start is the sensor, on Toyotas of his vintage the sensor is wired so that if it is unplugged the fans will turn on (providing the ignition is switched on)
Look to the bottom of the radiator, there will be a sensor with 2 wires. Unplug the sensor and turn the ignition to ON. If the fans go, the sensor is faulty, and is he cause of you fans not turning on when the engine heats up.
If the fans remain off, the next thing to check is the fuse. In the fuse box under the bonnet you should find a fuse or fuses labeled fan No. 1 and fan No. 2 (if air conditioning is equipped)
NOTE these are sometimes labeled RDS and CDS
The labels are on the underside of the fuse box cover. Check the fuse/s by either looking through the top if they are the square type, or pulling them out and looking through the side if they are the blade type.
If none of these fuses are blown there is an electrical fault that requires some electrical knowhow to diagnose.
The problem could be a blown AM1 or AM2 fuse, which you could also check, these are the battery feeds from the ignition switch to the rest of the car. Usually a blown AM fuse will mean other electrics will not be working either.
Another possibilty is a stuck relay, though highly unlikely, as they usually fail to work, meaning the fans will be constantly on. They're named fan No.1 and Fan No. 2 usually
You really need to understand how a relay works to check if there is a problem, for instance you can check if the relay coil is being energised by using a test light across the pins in the socket when the relay is removed. You can also check that ignition voltage is being supplied to the contacts of the relay while it is removed.
Toyota relays have numbers 1 2 3 4 & 5 for the pins on them. There is usually a small diagram on the relay to tell you which pin is which number, and possibly which pins are the winding and which are the switchable contacts aswell. In general, pins 1 & 2 are the winding, or activator in easier terms, and pins 3,4 & 5 are the switched contacts. Pins 3 &4 are usually common and are disconnected & joined with pin 5 when the relay is energised.
NOTE some relays exclude pin 4, and some replace pin 5 with pin 4, leaving only 4 pins in total.
To check the fan circuit with the relays removed, bridge across the sockets where pins 3 & 5, or if it only has 4 pins, pins 3 & 4 and the fan should turn on with the ignition switched on. If not, there is a problem with the ignition circuit.
Posted on Mar 16, 2011
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Posted on Jan 02, 2017
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