Car is an 85 TPI Corvette, but problem is pretty generic, so I figured I'd see if anyone has any ideas....

I say "weird" problem because according to my info, a Code 15 is the Coolant Temperature Sensor circuit seeing a "Low Temperature Indicated", yet the cooling fan is also staying running when light is on. I would think that if the ECM is seeing LOW coolant temperature, it surely would not have any reason to turn cooling fan ON?

I followed the troubleshooting tree for the Code 15...

Cleared code
Immediately upon restart the CEL is ON
Checked code
Code 15 stored

Cleared code again
Disconnected CTS connector and jumper the harness terminals together
Started car, immediately got CEL.
Checked code
Code 14 stored

According to troubleshooting tree, Code 14 at this point means faulty CTS connection or sensor. I replaced CTS and same exact codes and diagnostic results.

I checked voltage of CTS signal wire from ECM, with Key ON/Engine OFF
Reads 5.02 volts.

I again cleared codes.
I then totally disconnected harness from CTS and also disconnected jumper, leaving circuit "open". Even unplugged, I immediately got a Code 15 and cooling fan running.

FWIW, temperature on dash reads great, at 180 degrees +/- at all times once engine is warmed up, partially due to fan running all the time, I'd assume. No weird driveability issues or anything of that nature. No other codes stored either.

Any ideas?

 

pmed you

 

Figured it out.

Factory Service Manual says that if car gets a Code 14 or a Code 15 that the ECM automatically turns on fan. That explained that part of the problem. The culprit is/was a bad CTS weatherpack (or whatever it's called) connector.

 

my engine is getting code 15 and fans dont come on... still they do when i activate AC

 

bump

 

I also commented in your posting about t he code 15 your experiencing - his problem was his connector, so hopefully that will be yours as well. Just make sure the one you switching it to is good first!