1990 radiator fans

[epaul77055]

1990 #849 black/black--Houston,Tx- I have searched through previous posts, and looked through the solutions section and haven't found this problem discussed. About two weeks ago I went to start the zr-1 the battery was very, very low. (The battery is less than 6 months old-Auto zone black and yellow battery) Charged battery about 24 hours,battery took a full charge- car started like it normally does. As soon as the engine started both radiator fans came on (they do not come on when the key is on, only with the engine running. Went on a short drive (about 5 miles) hoping the fans would return to their normal state-they didn't. Checked for ccm codes (wire between A&g)no codes were displayed in the speedo area. I then checked the ac codes-none there.Checked the ecm codes (wire between A&B)Flashed 12 over and over. Pulled the connector and jumped the connector of the a/c high pressure switch fans still ran.I have disconnected the battery hoping something would reset- no help. Pulled the fuse for the ecm( I think) put it back in fans still run. Took one of the relays apart it was not stuck closed, no corrosion inside. Today I hooked up an Actron CP9145 no codes present. went to the view data section- I noticed a few thing I am not sure about the scanner says open loop,it had a section that said En freon--Yes was displayed to the right of that- not sure what that means. The one that stood out the most was oil temp it displayed 265- would that make the fans come on? (The oil was'nt hot the dash gauge had barely moved, car had been idling about two minutes) If anyone can offer any suggestions on what I should do next, they would be greatly appreciated. The car has about 63000 miles and has run perfectly the past 15 months. Thanks in advance epaul77055

[scottfab]

The coolant fans are operated by two separate relays
therefore I'd say they are being told to go on by the ECM.
When you pull either relay only one fans runs?

Are you absolutely sure BOTH are coming on?
And you say as soon as you start the engine?
The ECM uses three inputs for control.
VSS (speed)
Water temp
A/C High pressure side.

[epaul77055]

Yeah, I am positive both fans are running, you can unplug the relay on either one and the fan stops. You can switch the relays and they do the same thing.Just looked at it again took it for a drive --Car runs well normal start,good idle,secondaries working- water temp ok, oil temp ok according to dash gauges. Connected scanner to check temps-scanner and gauges were very close.

[scottfab]

I think you're going to have to do an investigation of the oil temp sensor and connector. The circuit description does not say the ECM looks at oil. It only says water but maybe that is incorrect
What does you data scanner say the water temp is?.

[gbrtng]

The one that stood out the most was oil temp it displayed 265- would that make the fans come on?
Look here first - my best guess is the oil temperature IS factored into the fan logic. Measure the resistance of the oil temp sensor - it's probably a dead short or close which would indicate high temperature.
Good luck ...

[scottfab]

Easy enough to test the theory of oil temp.
Just pull the connector and see if the fans stop.

[epaul77055]

Update: Finally figured it was the A/C requesting the fans. Replaced the A/C Fan pressure switch(the one on the small line closest to the firewall--Took less than 5 minutes) Fans are working properly. Thanks for everybody's input.

[Paul Workman]

Update: Finally figured it was the A/C requesting the fans. Replaced the A/C Fan pressure switch(the one on the small line closest to the firewall--Took less than 5 minutes) Fans are working properly. Thanks for everybody's input.

Good to know. Impressive set of troubleshooting skills you have there! Good yob mon!! Now...about that oil temp reading????

P.

[Livin' in the 80's]

Update: Finally figured it was the A/C requesting the fans. Replaced the A/C Fan pressure switch(the one on the small line closest to the firewall--Took less than 5 minutes) Fans are working properly. Thanks for everybody's input.

I fogot the GM ac deal. Is there a shrader valve behind the switch?

[epaul77055]

yes there is a Schrader valve-very little Freon was lost when putting on the new part. A very short hiss when taking old part off.

[epaul77055]

One other thing I remember reading, when changing the part have the new one close by in case the Schrader valve leaks a little- (then you can quickly screw the new one on and minimize Freon loss) I didn't have that problem- still working properly to this day.

[Livin' in the 80's]

yes there is a Schrader valve-very little Freon was lost when putting on the new part. A very short hiss when taking old part off.

My fans are on all of the time. I unplugged the connections and it still runs. does anyone have the fan wiring diagram? Both fans run with Marcs PROM in and all ac switches unpluged and the climate control off. Any input?

[Livin' in the 80's]

Update: Finally figured it was the A/C requesting the fans. Replaced the A/C Fan pressure switch(the one on the small line closest to the firewall--Took less than 5 minutes) Fans are working properly. Thanks for everybody's input.

How does that sensor work and how did you pin point the switch was bad? If I unplug all sensors, the fan still runs. I get full continuity at the two pins on the switch you are talking about. Is there a way to exactly see what temp the ECM is seeing from the coolant temp sensor?

[Livin' in the 80's]

How does that sensor work and how did you pin point the switch was bad? If I unplug all sensors, the fan still runs. I get full continuity at the two pins on the switch you are talking about. Is there a way to exactly see what temp the ECM is seeing from the coolant temp sensor?

Sorted it out. The green connector on the ECM wasn't seated all the way in and I didn't have the PROM snapped in all of the way. All works now.

Lesson learned - pay attention to detail!!!