Can some one help me here what problem could be????

i have dodge carvan 2001, 3.3 ltr engine, 186K on it,

Code is P1491....Radiator Fan relay ???

i check all fuses are OK,

Radiator fan runs fine with Air condition ON, but when A/C is OFF Radiator both Fan dont turn ON,

Even i drive for half an Hour on highway to test, it was hot, but fan was not running,

when i turn A/C switch on, they both start running ,

Any suggestion....what could be i should check next??????

is that Radiator Fan relay or some thing else. plz help me,

 

Code is for a fault in low speed fan relay (I can't remember if these fans have two speeds). However, if the fans run with AC on then the relay is working so I would go next to the cooling system temperature sensor (located next to thermostat housing). Check to make sure the electrical connector is tight and that the contacts are clean, if all is good there, then perhaps the sensor itself is bad.

 

I should have added you can check the temp sensor out with the use of a a volt/ohm meter. locate the sensor, and with a cold engine remove electrical connector, and then the using ohm meter, put one lead of connector on the A post and one lead on the B post (the posts in the connector, there are three, are arranged with the A and B across from each other, the C post is the top of the Tee Pee) and you should see 7000-13000 ohms, now run the engine up to operating temperature and do the same test and you should see 700-1000 ohms, if there is not a significant difference cold to hot, then the sensor is probably bad. Also check wiring from PCM to the sensor, but gut feel is if the fans run with AC on there is not a PCM wiring issue.

 

Thanks For Reply,

Here it is what happen, my Coolant level was low, i did not notice for Year believe me,

at one point i saw my temperature gauge went to hot my temperature lights turn on, i pulled my van and let it cool for little awhile, i open radiator cap and saw my coolant level was low, i filled it with premix coolant, i always carry one in my Van, and then i saw Coolant Bottle near battery , it was on low level too,

I filled it to proper Max level,

then i drive down to home, and went straight to a Electrician experienced one (15 years),

He said i will charge you $40 for Live data scanning than i can tell you what is problem,

So he did, he found fan turn on 105 degree temperature and off at 98 degree or 99, which is ok he said, nothing else was wrong,

he said it was low coolant which you filled in it, now your van is ok, nothing wrong with PCM, relay, computer etc, every thing is working fine,

he test the van for like Half an hour with scanner (snap on) (name says on it,) while engine was running , i was watching beside him,

seems to me it was low coolant, he was right,

but now my brain is clear from all doubts , which coming from reading lots of different thread, my van is so far running ok, i dont see my temperature level going to high.it remains on stable position.

Thansk for the help....