cooling fans not turning on

[1990lumi]

replaced all the relays under the hood have new cooling fan it works when hardwired to battery, but it does not kick on when my car is running and the coolant will boil over and spray out the radiator cap and overflow the coolant tank bad coolant switch or something else?

[RobertISaar]

cooling fans are controlled by the ECM, which gets its coolant temp information from the 2-wire coolant temp sensor near the thermostat housing.

 

you'll need to get datastream information to see if the sensor is indicating a coolant temp lower than reality or if the ECM is commanding them on at appropriate times, but they aren't engaged.

[Imp558]

try bypassing the relay by jumping 87 to 30 in the fuse box. If the fan comes on then probe the remaining 2 pins for power, should be 12V with ignition on present on one of the pins. The other goes to the PCM and the PCM grounds it to turn it on. If all is well then in theory you have a bad CTS, Like Robert said, the 2-pin one.

[1990lumi]

so either bad cts or ecm

[RobertISaar]

or a section of the harness requires attention.

[1990lumi]

i just need a second car so i can rip the motor apart rebuild it and replace every sensor and rewire a new harness in this one

[Turbocharged400sbc]

or a section of the harness requires attention.

 

THIS

 

for the 3rd time ive had a cooling fan issue on a car and it was the harness rubbed through on the upper dogbone mounts. for some reason the fan wires were all the way at the top of the loom and got rubbed through...lost 1 fan then the other.

[Imp558]

I don't know what year this car is but on my First Gen the fan wires come from below.

[1990lumi]

its for a 1990 lumina

[Imp558]

its for a 1990 lumina

 

Yeah, and for some reason I didn't figuere out that "1990Lumi" owned a 1990 Lumina all by myself. I gotta get back on the meds.