Power flows from Fuse #23 to the low and high fan relates. The control coils in the relays are grounded by the front control module. If the relays don't get ground, they won't switch the relay contacts and won't start the fans.
Start by applying battery power and ground to the radiator fan to see if it works when supplied power directly.
Yank the fan relays. Using a digital meter, check for battery voltage on terminal 86 in the low speed relay socket. You should see battery voltage. With the AC on and engine running, check for ground on terminal 85. If you're not getting ground the next question is: is the front control module not getting the command or is the front control module bad? Perform the same tests on the high speed rely. Battery power on terminal 85 and control coil grond on terminal 86
Did you check the fuse and the voltage at the supply side of the relays? How about the wiring and particularly the connectors? Also, it is not unusual for a new temperature sensor to be faulty - try jumping the contacts in the sensor connector to see if the fans activate.
I am assuming that you also checked the fuses for it to so now we have to check the wires and connectors check the wires for continuity and voltage from the pcm and from fuses in the power distribution box and relays also make sure that they fit tight in the connector inside the box so now if all fuses & relays are tight and the connectors are good and not broken and you have continuity through all the wires and no breaks are found under the power distribution box and from the temp sensor then the pcm fan controller chip has shorted out also did this start after giving someone a jump start or did you ground out the battery cables by mistake if so you might have blown a fuse link these are small gaged wires in the line that blow out to avoid over voltage from flowing through the system and damaging the pcm and components
SOURCE: 2001Jeep Grand Cherokee electric engine cooling fan wont turn off
relay sounds stuck...call a parts store for pricing
SOURCE: 2000 4.7L Jeep Grand Cherokee fan relay switch replacement
Go to this page:
http://rigs.corequipment.com/cebby_WJsite/cooling.htm#relay
Did you replace the sensor by the thermostat in the engine block or the one under the drivers headlight, There are two, the one next to the thermostat controls the temp gauge in the vehicle. the one under the headlight assembly controls the actual fans and is a electronic module. You have to remove the head light assembly to get to it.
Joe
SOURCE: 2001 Jeep Grand Cherokee Laredo- radiator fan
Remove right front headlight cut out the plastic right below where the headlight rest on. Just a 4"x4" square and take out the plastic there you will see the relay,2 screws and remove the relay. Patch the hole with duct tape and put the headlight back, no need to remove the grill or bumper.
SOURCE: 2002 jeep grand cherokee replaced radiator cooling
The
airbag light will come on and stay on as long as there is an active
code in the system, this means that something is malfunctioning right now so we will turn the
light on. You really
need to have the codes checked for an accurate diagnosis.
Its possible that you have some problem or your sensor go to bad...
1. Disconnect and isolate the battery negative cable. Wait two minutes for the system capacitor to discharge before further service.
2. From the engine compartment, disconnect the right or left headlamp and dash wire harness connector for the front impact sensor from the sensor connector receptacle
3. From the engine compartment, remove the two screws that secure the right or left front impact sensor to the sensor mounting bracket on the right or left radiator support vertical member.
4. Remove the front impact sensor from the sensor mounting bracket.
That is for replacement, you just reverse the list for install.
Hope helps.
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