Cat 3406e fan staying on

If your 3406e uses air to turn your fan ON then your fan should spin freely with your engine OFF. Newer trucks use air to release fans, that way fans remain ON when engine is OFF. You need to figure out what type of fan you have on your truck. My truck is 1998 and with engine OFF I can spin my fan.

 

Could be the fan itself, but more than likely you have a temp sensor reading high or an a/c sensor reading high pressure. Follow air hose from fan back to firewall where you will find the fan solenoid. You can use a test light and see if it's being powered on. That will rule out fan itself if something is sending power to it to supply air to fan. Good luck.

 

I understand that OP already tried disconnecting the air hose going to the fan clutch and it still stays ON.

 

There is a normally open solenoid and a normally closed solenoid. Don't know which he has.

 

Did you just recently wash the engine? My experience in the past when I soak the engine mine would screw up. This is especially true when the engine is cold but I have done it when it was warm as well.

 

Try tapping lightly on the fan clutch. I remember my friend's 6NZ fan clutch would not release. He removed it to repair and realized that his fan was already spinning freely. So my friend put it back on his truck and the fan has been working fine for couple months now.