rad fan wiring

[rustynuts]

my radiator fan will not come on, even if i pull the temp sensor while the engine is running. so, i pulled off the cover of the relay in the pcm for 'cooling fan' and pushed it closed, and it works.....so i know the power from the pcm to the fan is good. i tried using a paperclip to close the circuit in the temp sensor, and i got nothing. my question is, how do i go about fixing the wiring? does anyone have a wiring diagram?

[5-90]

1) What year? It's changed a few times, and you might want to get in the habit of giving with it from the off, so we don't have to ask you...

2) "Pulling the TFS" should not turn the fan on - if you have a TFS, it CLOSES to "make" the circuit. Pulling the wiring connector simulates an OPEN, which will not turn on the fan! That's why I've got a bagful of Delphi Weatherpacks with various pins bridged together - to simulate a closed switch...

3) Have you checked it with the A/C turned on? Even if the aircon doesn't work, the PCM gets an "A/C Request" signal that should turn the fan on as well...

5-90

[rustynuts]

its a 99 sport. i checked with the a/c on also, and had no luck. any ideas?

[5-90]

OK - check the fan directly. It's a DC fan, so you can hook it up backwards (it will just run in reverse) to test. Use a heavy +12VDC lead and a good ground, and see if it runs. If it doesn't, you need a new fan. If it does, try a new relay...

5-90

[rustynuts]

the fan works... i said that in my first post. it works if we push the relay closed with the cover off, or if i power it myself. it still doesnt work although ive replaced the relay twice before i ever took the cover off.

[goodburbon]

The newer model fans don't just come on like the older models. The ECU needs both the AC head pressure signal and the High temp signal.

[rustynuts]

my ac doesnt work either...... any ideas

[goodburbon]

If your AC doesn't work then the head pressure switch is not triggering and your aux fan won't come on. you could find out if the head pressure switch is just an on-off switch, and if it is just a normally open switch you could wire in a jumper. That would signal the ECU that the AC is pressuring up and once the triggering temp was reached the fan would then turn on.

[langer1]

The newer model fans don't just come on like the older models. The ECU needs both the AC head pressure signal and the High temp signal.

Not true it needs one or the other but not both.
Also there are two temp sensors, ones for the gage the others the engine temp sent to the ECU.

[goodburbon]

Not true it needs one or the other but not both.
Also there are two temp sensors, ones for the gage the others the engine temp sent to the ECU.

Gonna have to disagree with you there, mine wasn't coming on with the AC, and I took it to the dealership. It will come on if the jeep actually gets "hot" but not just with AC and not for normal operating temps <210.

[langer1]

Gonna have to disagree with you there, mine wasn't coming on with the AC, and I took it to the dealership. It will come on if the jeep actually gets "hot" but not just with AC and not for normal operating temps <210.

Thats what I said or at least meant

[rustynuts]

so what do i do in order to find out exactly what it is? im lost at this point.

[5-90]

Reading your original post again, I'd just try changing the relay. If you can manually close the circuit and the fan works, the relay is the next possible failure. High current through the contacts when they "make" and "break" can cause burning of the contact pads, and high connection resistance (to the point where the relay will no longer "make.")

5-90

[rustynuts]

i have replaced the cooling fan circuit and checked all fuses repeatedly...

[goodburbon]

Is your jeep overheating?

[rustynuts]

no, but it needs to be fixed. im getting a 1491 code, which says its the rad fan relay, which has been replaced

[Slo-Sho]

Pull the relay from the socket exposing the contacts beneath. Hit the A/C and verify the clutch is cycling. There should be 2 'hot' terminals one constant and one for the relay coil trigger. It will be easy to find the constant hot terminal for obvious reasons so you will be looking for that switched hot terminal for the relay coil. I would also use a digital multimeter (DMM) if you can get your hands on one. You can use a test light but do so at your own risk, test lights are for nOObs. Good luck.