1991 Other Oldsmobile Models Cooling fans won't turn on.

Did you check both fuses no.4 40amp and fuse no.16 10amp-if these fuses are okay and you've replace CTS. Its coming from the computer relay control high/low or the fan relay itself.

Checking the fan. Right cooling fan motor connect a jumper wire from the battery positive post to the red and blue wire at the fan connector and black wire to the negative battery post. Fan comes On -its either the computer or the relay.

I checkeed the fuses first, all good. The fan works, thanks for telling me which wires are pos. and neg. So it must be the relay or a comp. problem. I would like to know which relay controls the fan? There are 6 relays under the maxfuse/relay center panel under the hood. I checked the one directly under the 40 amp fuse, but it wasn't it. I am having trouble getting some of them off without cracking them. Is there any secret trick, and which one is the exact relay? Thanks a bunch for your help so far.

See 8 and 9 fan Hi/Low relays below

I checked the relay and its not it. I jumped the red main wire and the black/red wire at the relay and the fans turned on. I checked the brown wire with my multimeter and it has power with ignition on. autozone.com said it was either an open circuit or an ecm ground, but I have no idea where to look for those. Is there any way to ground the ecm again and where is the ecm located and the ground for it? You've been a ton of help so far. I might just wire the fan manualy, but I don't want to damage anything on the computer. I just think its wierd that if it is a bad ground there is no diagnostic light coming on. Thanks again.

Troubleshoot the fan circuit see below-The computer grounds the relay-when it sees the coolant temperature sensors input signal requiring the fan to come On.