Cooling fan wont run


New Member
Jun 22, 2021
My cooling fan will not run. I have looked at the troubleshooting guide on Vortex . Rlys 5 amp fuse is good. I have 12v always on large red wires at the the relays , and I have 12v on brown wire with key on. I have pulled the connector at the a/c, and fan works when A is grounded.
I jumpered between red and black/red wire on low relay and fan worked.
I located ground on back of wngine and seems to be de sound but hard to tell 100%.
Not sure what to check next.
None of the fan options work including the delay.
Thanks for any ideas.

Update. I have ran an aux ground wire on my 87 GN cooling fan to see if that would help but did not. I took the green wire on the low speed fan and cut into it to ground out that line. With key on the fan would come on. Does this mean the relay is good and it is not getting signal from ECM? I have ordered a new relay anyway. I thought perhaps ground line issue, but this should prove the fan will run. Looking for some advice. Thanks.
Thanks for the attachment pacecarta. I have this checklist and think I have done most of the checks. My car is all stock with no mods. I did get under the car and checked the ground lines and they were secure. Both constant 12v and keyed 12v are present at the relays. As per the checklist , when I ground the a/c switch on A and B, the fan will run. The fan does not run when I switch on the A/C, but my A/C hasn't worked for many years. ( may affect this reading) When I pulled the temp switch and ground it, the fan runs, but doesn't shut off until delay is done. I know the fan runs and wiring to it is good. I believe the ground is secure.
I did cut into the green wire on the low speed fan and grounded it and the fan ran. The checksheet says if the fan doesn't come on, its the relay. If it does come on as mine did, does this mean it is the ECM? Can just this portion of the ECM fail? Thanks for any more input.
Check connector C1 pin D2 on the ECM wiring the dark green wire. The connector is labeled where the wires go in and it's hard to see.
Remove the ECM plug C1 and find the D2 cavity and ground the dark green wire at the socket with it unplugged, if the low speed runs the ECM is the problem. And yes the driver can be cooked that turns on the fan relays.
It can also be a corrosion problem or the ECM not knowing what the temp. is but the car probably wouldn't run well if the temp. sensor is faulty, do you have a scanmaster and do coolant temps. rise normally while warming up?
Thanks for the reply. I do not have a scanmaster, I have been looking into it. I was leaning to the Scanmaster G to get the downloading capability??
I will check the dark green wire at D2. I guess this is the wire I cut into at the relay and will eliminate a broken wire being the issue. Not looking forward to buying a scanmaster and a ECM.
Thanks again for the info.
if the terminal was clean and had good contact to the cm pin and the ecm (escanmastr) says coolant temp over the turn on temp then the ecm is the issue
try reinstalling the chip or try another chip as the ground is triggered by the chip , if that wont fix it replace the ecm
As mentioned the chip set point determines the turn on of the low speed fan. Is it a stock chip?
You need to see the coolant temp. on a scantool to make sure the ECM sees the correct temp. for fan turn on that is programmed in the chip. The two wire coolant temp. sensor sends that data to the ECM. At least you know the wiring is good but need more data to determine if it's the ECM or not.
Hint, get the scanmaster, and I'd get a modern chip even if running stock injectors too.
Yes, it is a stock chip. I did check the coolant temp sender with my ohm meter at a couple temps and the resistance was increasing as my engine cooled down so appeared to be operating correctly, but that doesn't mean the data is getting to the ECM. I will get a scanmaster. What is difference between my old chip and a new one if it stays stock? And thanks again for the help.
I just got my scanmaster. The scanmaster is showing the coolant temp properly. I assume then that the ECM is getting the data , but the fan will not run. I ran a ground wire from the dark green wire on the low speed relay to a switch and the fan will run manually. I feel that all is working except possibly the ECM is not grounding when the temp goes up.