Chrysler Repair: Radiator fan runs all the time: 98 minivan, chrysler grand voyager, upper radiator hose

Question
I have a chrysler grand voyager r reg 1998 year 3.3cc.
The problem is when i start the car up the fan starts up and does not stop untill i turn the engine off i have replaced the relay which is under the air filter what else can it be?
Thank you

Answer
Hi Lee,
The powertrain controller operates the relay. The signal to activate the relay has two possible sources: the coolant temp sensor and the AC system pressure sensor. I would begin with the former. It is located near the upper radiator hose manifold on the top of the engine. The 2-wire connector has tan/black and black/light blue colored wires. Measure the resistance across the terminals of the sensor when the engine is cold (should be 7,000 to 13,000 ohms) and hot (should be 700 to 1,000 ohms). The pressure sensor appears to be located near the firewall (at least the picture shows a belt driven device near by) in the coolant liquid line and has a three wire connector: dark blue, violet/white, and black/light blue. The violet white should have 5V on it, the black/light blue is a sensor ground wire, and the dark blue will have three possible voltage levels depending upon the pressure in the line. (ranging I suspect between 0 and 5V). You could probe the dark blue wire to see if you are getting different voltage levels depending upon the operation or not of the AC compressor.
Other than the sensors, it would mean checking the wires from the sensors to the powertrain controller for continuity. I can give you those pin assigments if necessary
Roland