Thread: Radiator fans wont come on

This happened a while ago, for what ever, they stopped working, causing the car to get very hot when stuck in traffic. So far, ive check all fuses, relays, replaced the coolant temp sensor, and put new coolant in and bled the system, They will kick on if i unplug the coolant temp sensor, and randomly some times, but hardly ever, Any ideas? (no they wont come on with AC because my ac does not work.)

What year? and do they come on EVERY time you disconnect the coolant temp sensor?

1997 and not immediately but yes

Sounds like an electrical issue somewhere. Do you have a meter? I'd start with looking at the wiring at the temp sensor and look for any breaks or worn wiring under the loom.

yes i have a meter, and alright ill check it over this weekend when i have some time

Originally Posted by Turbocharged400sbc

ect sensor resistance is easy, make sure that you have the correct 2 or 3 pin sensor, if your car has the ECT pigtail that the harness side is plugged in is the same, the pigtail will have 2 or 3 wires. seen plenty of problems with motor swaps/etc in that area... but if the sensor side shows fine (pcm is see'n 215*+) then it should have no problem grounding the relays. now onto the control circuit testing.

go to the junkyard and grab a spare pair of fan relays (if yer a ham fisted bungler), remove the covers, verify secondary circuit activation manually (squeeze relay closed)
if both function, probe primary side s of relays for +12v KOEO. the pcm grounds the relay primary circuits to turn on the fans. if secondary side is fine and primary side has power, then you need to check continuity to the pcm.

id bet the harness rubbed through somewhere, ive seen it 4 times so far

No offense but a lot of this did not make sense, as i am fairly new to automotive mechanics. My coolant temp sensor pigtail has 3 wires, from what wires wernt covered, i couldnt see any wires that rubbed together. i verified all relays are operating correctly with the help of my friend, a multi meter, and some jumper wire, all checked out. as for when you say "check the continuity to the PCM, how do i do that?

This is what I did on mine. Keep in mind mine is an 04. My temp gauge went out so I figured it was temp sensor that went bad. I changed it out twice and it still wasn't doing anything so I knew then that it was a wiring issue. I took out the pcm and checked the resistance where the wires from the temp sensor connected to the pcm. (I peeled back all of the wire loom and traced the temp sensor wires all the way to the pcm and wired some small gauge wires to the probes on the meter since the probes are too fat to go into the pcm slot things or whatever you call them to get a reading.) It read 0 so I knew the signal was not getting to the pcm meaning there was a break in the wire somewhere. If you put the probes from the meter into the sensor itself, you will see a reading. What the reading should be I honestly don't know but you should see SOMETHING. What you should be seeing is another question. What you want to do now is make sure that you are getting a signal to the pcm from the temp sensor and then worry about what you should be seeing. If you get a 0 reading at the pcm with the sensor connected, then that means you have to find the break in the wire. Since you already peeled back the loom and have the wiring exposed, trace the entire length of the temp sensor wiring and look for any corrosion or nicks or cuts everywhere and be very detailed when you look because my break in the wire was EXTREMELY small and I overlooked it twice before I found it.

Originally Posted by luckyg817

I took out the pcm and checked the resistance where the wires from the temp sensor connected to the pcm. (I peeled back all of the wire loom and traced the temp sensor wires all the way to the pcm and wired some small gauge wires to the probes on the meter since the probes are too fat to go into the pcm slot things or whatever you call them to get a reading.) It read 0 so I knew the signal was not getting to the pcm meaning there was a break in the wire somewhere.

Hi, nooby here, this is a BAD ASS reply, as it was clear on how to follow, one question, when you said "wired some small gauge wires to the probes on the meter since the probes are too fat to go into the pcm slot" do you mean, with the wireing harness unplugged, use the meter prongs to touch the spade terminals on the PCM? Or with the wiring harness plugged into the PCM, peel back the wire from the temp sensor and take readings off the exposed temp wiring, orrrrrr just stick wire into the female socket of the wiring harness, and take readings from that using the multi meter

You see in the pic where I have the alligator clips? Well let me correct myself by saying that I actually used some staples to be able to get to the terminals since the probes are too fat. You leave the temp sensor plugged in and you test the resistance at the pcm connector as pictured above. You should get a reading at the terminals. If you don't, you have a break in the wire somewhere and that's what you need to find. Think of it as a water hose. You should have water going in at one end and should be coming out of the other. If you don't, you have a leak somewhere. Same concept with wiring. Hope that makes sense. If you have anymore questions, let me know.

Originally Posted by luckyg817

You see in the pic where I have the alligator clips? Well let me correct myself by saying that I actually used some staples to be able to get to the terminals since the probes are too fat. You leave the temp sensor plugged in and you test the resistance at the pcm connector as pictured above. You should get a reading at the terminals. If you don't, you have a break in the wire somewhere and that's what you need to find. Think of it as a water hose. You should have water going in at one end and should be coming out of the other. If you don't, you have a leak somewhere. Same concept with wiring. Hope that makes sense. If you have anymore questions, let me know.

Got it, my problem is i was thing of the current wrong, Power comes from the temp sensor, to the PCM, PCM reads the temp, evaluates if its hot enough to kick on the fans, but if the power cant make it there, then it wont kick on the fans, got it! how did you rewrap the wires though? just re-tape wrap em and buy another cord cover?

Yea pretty much. There were parts where there was tape under the wiring loom holding the wires together so I reapplied new tape to where the previous was at and then reused the same wiring loom and then taped that with new tape. You pretty much want to put it back the same way as when you took it apart. I also taped the sensor wiring where it will stick up instead of leaving it hanging down below to keep it from possibly touching that crossover pipe or touching something hot and melting the wires.

Update: I had a more experienced mechanic look at it, apparently what my computer sees my temp as and what my gauge reads are two different things, temp gauge is reading hotter than what it actually is (reads 230, actually 208), where should I look first into an incorrect gauge reading?

Yeah it's brand new but you don't think it could be the cluster? Mine seems
to have a lot of issues, gas gauge, right blinker indicator doesn't work, rpm gauge bounces when car is off

The fans come on now, they come on when my temp is reads about 230 on the dash, so just the gauge is ****ed up

I did that today, gauge in inaccurate, my question was, short of installing a aftermarket coolant temp, what can I do to make my gauge correct