Radiator fan always on

[hinge]

I'm working on 1989 Grand Prix 3.1, cannot get codes, check engine light not working (bulb has been swapped) this fan always runs , even at cold start, is it the ecm via the coolant temp sensor that turns this on or is there a sensor at the fan sensing radiator temp, don't know if I'm in the right forum

[CNCguy]

The fan is controlled by the ECM which gets the temp from the engine. Is this a new problem or could someone have wired it to run all the time? Will the engine start and run? Does the CEL come on at any time? A defective ECM or chip can cause the fan to run at "key on" when the engine is cold. Does the fan come on before you crank the engine?

[bszopi]

The fact that you can't retrieve codes tells me its something with the ECM or PROM.

[hinge]

Fan sometimes comes on when you 1st turn key, and it has come on within 1-2 minutes after engine start. The original prob was stalling engine. So ended up replacing IAC , then had high idle, tried idle relearn and thats where I read about ecm needs to see fan go from off to on to set idle (?) So before I go further on idle , I wanted to get fan circuit working . Also swapped fan relay with no change

[robertisaar]

does the TCC lockup? if the ECM or PROM is junked, the outputs are disabled, meaning ECM controlled stuff is essentially disabled.

and idle learn: the fan needs to come on, then shut off. during the fan starting/running, the ECM starts adjusting the IAC position, learning where exactly it should be at a hot idle, and when the fan disables, it pretty much stops learning where it should set the minimum.

[hinge]

what's the tcc lockup? this car runs great, except for idle, so I'm thinking the ecu/eprom is good

[86FieroSEv6]

Does the check engine light come on with the key on and the engine off?

[hinge]

I noticed today the CEL comes on for barely 1 second @ key on engine off, then goes out. I then jumper A B pins on aldl port and still get no CEL flashes

[robertisaar]

sounds like the ECM or PROM is junked.

[86FieroSEv6]

The check engine light should be on any time the key is on and the engine is not running. That, coupled with the fact that you cannot retrieve flash codes along with the fans being in an always on state leads me to believe that your ECM is "critical fail operation" mode, sometimes referred to as "limp in" state. Please verify powers and grounds to the ECM before replacement.

[geoffinbc]

Did you check or diagnose the temp sensor?

[walterdude]

FWIW: One time on my 93 Z34 (OBD-1) I forgot to connect the wire that goes to the coolant sensor and the fans ran all the time... Forget if it threw any codes or not.... Was a few years ago,, probably 6-7 years... At any rate just something to check,, disconnected wire/bad sensor...
Good luck,,,
Tom..
I also believe that the fans run when the A and B are jumped for code retrieval...

[robertisaar]

]
I also believe that the fans run when the A and B are jumped for code retrieval...

this is true. the low-speed fan is supposed to kick on during code retreival.

[hinge]

Thanks everyone for info, I will troubleshoot temp sensor next, then do reading on ecm swap, we found several Grand Prix's at local junk yard