Radiator fans run constant with key on and a cold engine..

[major7venth]

Radiator fans run constantly with the key on, even with a cold engine.. Installed new temp. sensor, same thing..Disconnected the temp sensor and the fans will stop. Cleared any codes, turn on the key fans now would operate normally (when they needed to) when engine coolant temp was up. After starting and driving and letting cool, fans again run constantly even with a cold engine.. I find no error codes for this and anybody know why and how to fix this problem? Do I have a bad 'new' temp sensor? voltage at the sensor pins..should be what?
M7

[svxistentialist]

Another possibility is aircon problems.

When the aircon is switched on the fans come on to keep the condenser up front cool. Have you checked if your aircon is switched on when the fans are on with engine cold?

Or you could have a fault in the aircon computer. Do a search for the method of downloading codes from the aircon system.

Joe

[Hondasucks]

if I remember correctly you press and hold the "OFF" and "RECIRC" (or "AUTO" and "RECIRC") buttons and turn the ignition on to initiate the self test. There is a thread about AC problems on here in which I posted a PDF from the service manual on how to do it, along with all the tests and such.

[Hocrest]

Is your power light flashing when you start the car? A bad speed sensor can cause the fans to run all the time.

[major7venth]

Very good suggestions... I had run aircon diagnostics, no error codes. Always started the car with the A/C off.
Speedo has never worked as Internal trans. speedo gear does not turn and, no speedo. I have spun #2 speedo sensor with a variable speed drill motor, sensor and speedo works fine although, no speedo input to the ECU while driving.
This problem occured for no apparent reason, (no new codes) car has never had a speedo since we bought it. Not sure if the power light flashes, I'll check that next time I get close to the car. I have a service manual set to refer to and could not find anything on this particular problem.. The error codes I have are both knock sensors (been that way a long time too,) (Anyone ever try fashoning a wiring harness and plug #2 speedo sensor wiring into #1 speedo sensor?) no sure if rear trans. revolutions (or voltages) are different from the front. If they were the same, may be a temporary fix for the speedo, maybe).
After clearing any codes the fans will run normally (not come on when cold) then after warm up and cool down they run again...I have checked all those things suggested.. *and still the fans run on*.
Thanks for the help everyone..
M7

[benebob]

Try unplugging your coolant temp sensor for the fans. I believe it is located on the radiator itself but may be around the return from the engine on the SVX. If it stops when you unplug it then that would be you're problem.

[major7venth]

Yes, I installed a new temp sensor (located top,behind intake manifold) as I determined that was the problem and could be nothing else..fans run on. (I have unplugged temp sensor while running and the fans would stop (as they should). Plugged back in and fans run on. I even disconnected the battery and turned on the key as a hard reset..after warm up and cool down. Turn on the key (engine cold) fans run on.
Thank you for the help.
M7

[svxistentialist]

Major7

if you accept that your temperature sensor is new and is OK [although it is vaguely possibly that a brand new one could be faulty or damaged] then we need to look elsewhere.

It occurs that your speed sensor may be causing the problem without throwing a code.

If the ECU is expecting to see a signal from your speedo feed, and currently you say your speedo is not connected, then possibly that could be your problem.

If you think about it there could be a subroutine in the ECU that is written to keep the engine from overheating. If the ECU thinks your engine is running all the time, but the car is parked [speed = 0] then naturally it is to be expected that engine heat will build up, and the fans need to be active to keep from overheating. So it could be a failsafe programme, like the limp home mode of the TCU.

This is speculation on my part because there is no information to hand to define what is written in the ECU. However, with a funny electrical happening like this it may be impossible to troubleshoot unless you connect the speedo and attend to the recurring codes.

Joe

[major7venth]

Joe;
Good thoughts... I swapped the 92' temp. sensor with 94' (car with the problem). 94' still same problem. 92' runs normally. So it's not temp. senor. (I had initially installed a new temp. sensor assuming 'that was the problem' simple fix...not). So the temp. sensor is good for sure. (Probably could have used multi-meter and checked voltages/resistance to determine IF I temp sensor problem too, i guess).
Speedo has never worked, so this problem arised for no apparent reason and no codes.
I considered it is a default ('subroutine in the ECU')(limp home feature, or something, etc.) for the fans to run constant, if there is an error and no new errors..
Again, if I clear the codes, fans run normally until car is up to temp and fans start running, after cool down (to cold) turn on the key and they run constant. I checked the book, changed parts around, cleared codes, did as much as I could, (I think I will check fuses,just to say I did) for these reasons I am asking here, someone must have had this problem before.
thanks for the help..
Jacob (M7)
P.S. If you enjoy cars...check this website http://www.clenetcorner.com/
I built most of em' back in the late 70's, 80's. them's were the Glory days!...enjoy!

[Hocrest]

Originally Posted by major7venth

Again, if I clear the codes...

what codes are you getting??

[major7venth]

Error codes are #22 and #28. (had these codes prior to the 'constant fan on' problem).
I do not have a #21 temp. sensor error code. (I'm am sure temp sensor is functioning normally).
many thanks for the help
Jacob (M7)