Nissan Repair: coolant fan, coolant temperature sensor, nissan sentra

Question
QUESTION: i have a 1994 Nissan sentra 1.6i and when the coolant fans comes on they don't turn off . what might cause that?

ANSWER: James,

The coolant fan relay is probably stuck and in need of replacement.  THere are two fans.  One is for the cooling and the other comes on with the airconditioning.  You could swap relays to make sure before you purchase a new one.

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QUESTION: i have replaced the two relays and also the coolant temperature sensor and the fan still will not turn off

Answer
James,

If the relay and the sensor has been replaced the computer is commanding a ground for the relay.  Now, you might have replaced the temperature sensor that tells the dash gauge or light to operate and not the one that tells the computer to ground the fan circuit.  Here is a quick check. With the key in the on mode remove each relay to see if the fan will stop.  If it does then check to see if the temperature sensor you installed causes the fan to turn off too.  If unplugging the sensor kills the fan you know you replaced the right sensor.  Now if the aforementioned does not correct the problem it could be that the ECM might be defective.  To check this, get a Haynes Manual to read the schematic and follow the circuit from the fan relay to determine which grounds when given signal from.  Once you find the circuit backprobe it to see if the ground is on constantly.  Email me back as I would like to know what you find.