What could cause a fan to run constantly? Once the key is turned on, the primary fan runs nonstop until the key is turned off

Could a faulty temp sending unit have failed and causes the computer to constanly think the car is running hot?
The car definately isn't running hot since it does this from initial startup even when engine is cold.

Anyone have a few tips to check into the wiring/sensors/sending units/etc or a detailed wiring diagram for a 1988 Iroc/305 TPI?

Thanks.

 

Wiring diags: http://www.austinthirdgen.org/index.php?pid=19

As I understand it, the ECM gets temp input for the primary fan from the coolant temp sensor which is usually right by the thermostat housing. It could have gone bad a telling ECM that car is hot when it's not - anything is possible.

 

If the fan is on all the time the key is on then either:

1. One of the sensors or relay is bad so the fan went into the automatic default mode.
Then it will run all the time the key is on.

2. The previous owner modified/rigged it that way.

Are the wiring or relays modified or tampered with in any way?

 

I didn't want to add any doubts, but the harness was gone over by myself one winter before I installed it in my car w/TPI swap. I carefully went over everything and traced wires/etc to keep everything except the pollution crap that I am not running. I also knew that eventually I would be going to a serp setup, so I wanted to leave the cooling fan wiring in tact. As far as I know, nothing is out of place that is why I was hoping that maybe I could ohm(?) or test the coolant sensor to see possibly what signal it is sending to the computer or?

Thanks guys for the replies and if anyone has anymore advice/info please do chime in.

 

Has it always worked this way since you've owned it, or is this a new development? If it's always been that way, check the fuse box for extra wires, or any alteration of wiring at the fan relay. In the technical article section there is a description of the stock fan set up, check it out as well

 

So, can anyone offer any tips as to how/if a person can check a temp sender to see if it has failed or is sending the wrong signal?
Can they simply be ohmed out and if so what are the proper specs?

 

Mine just threw a code 15 and the fan stays on, try replacing the sensor and your problem should go away.

 

I have wanted to add the elec. fan and do away with the bulky clutch fan for quite some time so I just did it anyways and I am just going to live with the fan running constantly until I get it figured out I guess.
I checked voltage at the relay via the 2 smaller wires (green/white- and tan/white+) which from what I understand control the relay's open/close action and as soon as the engine is started I get ~14volts~ and the fan kicks on instantly and runs constantly until the key is clicked back one click (meaning engine OFF but key still forward enough so all acessories like the radio etc are still functioning).
This is where I am confused:
I'm thinking the relay has nothing to do with it, but if the coolant sensor is bad then why does the fan continue to run even when the sensor is unplugged? Wouldn't the relay need the *negative* ( - ) signal supplied by the coolant sensor to even operate at all?

Anyone have any opinions or have a better understanding as to what is happening here?

 

Hmmmmm....

I tried two spare (used) senders I had from spare TPI manifolds with no change. I know it would be best to just spring for a new sender, but I have a hard time thinking 3 senders are all bad(?)

What is the best way to check the relay to see if it is in fact in "automatic default mode" like someone mentioned above....or IS there any way to check for this?
(*praying for a response by someone*)

 

WELL MINE WENT ON THE FRIZZZ SOOO I REPLACED ALL THE COOLING (HA HA ) GOT BRASS RADIATOR AND FLEX FAN AND SPACER AND BASICLY TOOK IT BACK A DECADE LOL.... BUT IT WORKS AND BEATS SPENDIN 150$ FOR NEW FAN + THE NEW RADIATOR I NEEDED LOL

 

I've never heard of any "automatic default mode" on any electric fan. They either get signal from the relay and work, or they don't. I suppose the ECM could send a constant signal if it could not detect any temp reading from the CTS, but I've never heard of it.

If it runs all the time, chances are it's been wired that way by a previous owner (99 out of 100 people rig these fans to run always because they are too lazy/stupid to figure out why it stopped working). Your going to have to start tracing your wires down and see what has been hacked in the past if you want it to operate as it is suppose to.

 

(1) of my (2) fans work the same way, it starts running before the engine is even running. As soon as the ignition is switched to "ON", it starts going. 87SSTPI, did you ever find what was going on with your car? I have looked through the wiring on my car, and there is nothing obvoius that was hacked up (believe me, it would be obvious if it was, gauging all the other wiring jobs done on this car, the amount of extra wiring I pulled out of this this was crazy). Could it just be that the relay is stuck in a closed position? I will try switching the relays tonight. This has worked like this since I've owned the car (bought used).

 

No, I am still just running it as it is and the fan runs constantly whenever the motor is running.
It doesn't really hurt anything I guess, but it does bum me out a little considering I left all that wiring in tact when I went through the harness for my TPI swap just to have it not work correctly for 'whatever' reason
If I would have known this ahead of time, I would have just eliminated that extra wiring and went with a custom fan control.
The lack of info on how to test any of the components of the cooling fan electrical system (relay(s)/coolant sensor/etc/etc/etc) is why it still remains as is.
I don't feel like wasting money on electrical parts that I don't need since electrical parts are non-returnable for obvious reasons.
If you happen to find a cure, please chime in if you think of it.
Thanks.

 

The CTS is what is causing the fan to run. Sometimes the wires in my connector back out, try pushing them in or wiggling them. Otherwise check for a bad ground to the sensor.

 

Try swapping the ecm. You need to hook up a scan tool and see what the hell's going on. Got any codes? Does the ecm still flash code 12?

 

before doing all of that, try unplugging the coolant fan switch. It's on the passenger side head. If you unplug it, and the fan still spins it is not that. If the fan stops spinning when you unplug it, replace the fan switch. I had this same exact problem.
Takes 2 mins to do and I am almost sure that is the problem...

If it is not that, than I have no idea!

 

Ok, this may not help you too much, but I did find out why mine was running all the time. I went to switch the plugs for the (2) relays on the driverside firewall, I knew one of the two was the fan relay, when I did, I noticed one of the wires (thinner gray wire) going to one of the relays had a tap off it that was grounded right to the relay bracket. Once I left that wire ungrounded, the fan did not kick on when I set the ignition on. Now all I have to do is get this car running and make sure it does kick on when it is suppose to...

 

get a scan tool on it and skip all the guessing

 

Hey guys, I have the same fan running issue, recently acquired 1.00 purchase (electrically hacked up) 91 RS 305 TBI, to jump to the chase, i found the same piece of scrap wire grounding the green with white stripe wire of the plug right to the bracket on drivers side firewall. when removed fan quits. I did notice a broken green with white stripe near the starter, just hangin out..same wire? wondering what ever happened to the resolution of this thread….

 

For what it's worth, I ended up eventually just using an aftermarket fan controller. Since this thread is now from over 5 years ago, I don't even have TPI in my car anymore. Sorry, I know that doesn't help you at all, but at least you know for sure that I never did figure it out

 

Again this an old post but I have a 91 Z-28 305TPI and had the same problem with the fan running all the time. I knew the manifold temp sender was broken when I bought the car and was getting a code 15. I just replaced it and that stopped the fan but now the fans don't come on at all. The temp gage goes all the way to 260 and then eventually comes down to 190-200 I am thinking it may be a thermostat. I turned on the A/c, no change.
I obviously know at least one fan works but thought I would post this to ask what the next thing to check would be as I think the fan(s) should have been on.
Thanks for any help.

 

I second the response about it being rigged up to do that. I had the exact same problem where my fan was running with just the key in, I traced the wires and found a bundle of black tape right before the relay. Under the tape I found that they crossed the wires to make it run constantly.

 

Relays can stick on also.

 

Coolant fans have always been a problem, that is why there is an 8 page troubleshooting guide and 6 pages of schematics in the GM Firebird service manual. Something everyone should have as they are pretty cheap.