1997 Dodge Neon. Radiator fans nut running, check engine light on (codes: rad. cooling fan circuit; battery disconnect). Fuse OK, replaced relay and temperature sensor (at rear end of head). Temporary switched hook-up to battery proves fans OK. (Cut two wires at the fan end of connector so original connector could be used with the switch hook-up. Switch inside car).
After warm-up, no 12VAC at the fan wires. Temp gauge works OK.
My understanding is that there are two outputs from the sensor switch in the head, one for the gauge and the other to the ECM, which in turn a)Turns fans on, and b)controls idle during warm-up (Engine does not keep running unless I give it some gas; a little easier to handle after warm-up). With relay and sensor both new, and the temp gauge correctly indicating, I am presuming that either there is a bad wire/connection somewhere or the ECM is faulty.
Hoping it’s not the latter, I have this question:
With the fans still on my temporary ON/OFF switch and its wires from the relay not connected to them, can the computer detect that the fans are not connected to the relay by way of detecting resistance through the fan motor(s) or some other kind of magic? Must the fans actually be plugged in before the ECM turns the relay on? Or should I be getting the 12VAC reading at the cut Black & Green wires?
Go to www.autozone.com and register you and your car. Then come back here and click on this link to the radiator fan relay wiring diagram, Fig. 5 http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Wiring+Diagrams&partName=Chassis+Electrical&pageId=0900c152800793b2&partId=0900c1528007934d
Fuse #5 supplies 12 volts to the solid state relay on the GY (gray) wire. Check for the 12 volts. The pcm turns the relay on over the DG (dark green) wire. With the engine hot, check for 12 volts on the DG wire. If there is voltage on both the GY and the DG wires, If you can’t/won’t use a multimeter, you need someone who can.