94 Corolla electrical problem (Fans)

[mz_jop]

I have a 1994 corolla...

When I turn the engine off (onto Off or Acc) the radiator fans start up and will not stop unless I disconnect the battery.

while the key is in the 'on' position and the engine is not running, the fans don't run.. If the engine is running, the fans seem to operate as normal, coming on periodically to assist in cooling.

So I suspect the thermostat is working ok, and the relays for the motors themselves seem to work ok (I tried taking out the relays one at a time and one motor would stop working, whilst the other would still start up when the ignition was off).

So my suspicion is that there is a higher level relay somewhere that controls the engine subsystem that is remaining closed when all the rest are off - I noticed that disconnecting the thermostat sensor starts the fans up regardless of the state of the ignition - perhaps when the ignition is switched off, the system controlling the thermostat turns off and the other system which is remaining stuck on decides the fans need to turn on

This is all a bit of a hypothesis at this stage..

My question is: Are there any 'higher level' relays that I can easily check and replace, and where are they?

I've searched high and low for a wiring diagram, I'm actually an electrical engineer (not automotive electrician though so I'm comfortable with such diagrams.. if only I could find one... are most cars the same? would a diagram from a similar vehicle be useful to at least understand how these systems work? (I've got the wiring diagram of a 1977 corolla, but I'm not sure there's that much overlap

Any help would be greatly appreciated

-MZ

[WissNX01]

YOu know, radiator fans are also designed to stay on after the car is shut off. This helps in cooling the engine even faster. Now, are you worried because it does this? Or are you worried that the fans stay on for longer than say 30 minutes. After 30 minutes, I would worry about 1) bad thermostat or 2) a open connection or relay.

You need to check first that the fans are suppose to do that. If not, check your thermostat. A bad thermostat will send a signal to keep your fans running. If its wiring or a relay, I would worry about that last. since electrical is a lot harder to diagnose.

[mz_jop]

Originally Posted by WissNX01

YOu know, radiator fans are also designed to stay on after the car is shut off. This helps in cooling the engine even faster. Now, are you worried because it does this? Or are you worried that the fans stay on for longer than say 30 minutes. After 30 minutes, I would worry about 1) bad thermostat or 2) a open connection or relay.

You need to check first that the fans are suppose to do that. If not, check your thermostat. A bad thermostat will send a signal to keep your fans running. If its wiring or a relay, I would worry about that last. since electrical is a lot harder to diagnose.

Definately not a thermostat issue... while the car is running, the fans are often off, but if I just sit the car still and rev the engine the fans will eventually come on for a short time to cool the engine..

They may well be designed to run briefly while the car is off (which is maybe why they're still able to receive power), but they've already flattened the battery once by staying on (this is how I realised there was a problem and this morning I plugged the battery back in and they immediately started up again.. - cold engine

There may be a fault in the thermostat switch, but it only causes a problem when the key is off or on 'accessories' which indicates there is something else going awry (if I unplug the thermostat wire, the fans are on all the time, regardless of the position of the ignition or whether the engine is on or off

anyway it's a moot point now, taken it to the autoelectrician

[WissNX01]

Damn, your going to pay out the nose for something that could be easy. Depending where you live, YOu can pay upwards of 200 bucks for this guy.

[mz_jop]

Originally Posted by WissNX01

Damn, your going to pay out the nose for something that could be easy. Depending where you live, YOu can pay upwards of 200 bucks for this guy.

hehe it cost 95 AUD (about 60 USD) it was a control relay... might suss out a manual in the shops tomorrow to see if I can see which one it was (it wasnt the motor relays)

[WissNX01]

Sorry, I was thinking US Dollars. Hey, a relay, see. Did he replace it, or just find the cause of your problem?

[mz_jop]

Originally Posted by WissNX01

Sorry, I was thinking US Dollars. Hey, a relay, see. Did he replace it, or just find the cause of your problem?

yeah just replaced it... it was like 60 bucks for the relay and 30 for labour

[WissNX01]

Hey, thats not bad. Did you run your car around to charge the battery, or do you charge it seperatly?