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Please help going nutz

my son has a 1998 dodge intrepid 2.7 the cooling fans wont come on. has a new radiator, new water pump, new thermostat,new hoses, new fan relays, new temp control sensor. I have jumped the fan to battery and they work. checked all other fuses and wires and all look good. neither fans work. doesn’t matter if a/c is on or not. cant figure this out. if it was just the a/c I would say its the a/c pressure transducer. but the fans wont work anytime except if I go straight to the battery. please help. thanks in advance

The power train control module controls the fan relays.

So if you’ve eliminated fuses, relays, and the sensor, that’s all that’s left.


The fans should turn on @220 F or 250 PSI A/C pressure, how hot is the engine?

the car will overheat

The temperature reaches 250 F? If the cooling system cap is left off for refilling the cooling system, the coolant will boil before the fans turn on.

With a scan tool you can observe the temperature and A/C pressure, also the cooling fans on/off state as commanded by the computer.

there is only a cap on the overflow tank. if that cap fits a little loose will that cause the antifreeze to boil over? also a code for the a/c pressure transducer was present on my scan tool. im planning to change it. that’s probably why the a/c fan doesn’t come on. im more concerned with the drivers side right now.

The cooling system cap on the reservoir should be a 16 PSI cap, that adds 48 degrees of boiling protection. Without the cap holding pressure on the system it will boil at 220F (or less). The upper radiator hose should be hard at this temperature indicating the system is holding pressure.

Both fans operate together, low and high speeds. The PCM can’t switch on just one fan. If only one fan is working you have a failed motor or wiring connector.

both fans don’t work. I ran wires from battery to fans and they work

This car uses a fan controller. Go to, look up year,make , model, and engine. The one you want is the Hayden preset one. $19.97 + tax and shipping. You will see a pic of it on the site that will help you locate it. I am sure you can buy one locally if you want but it helps to see the part first.

When owning junkers I will hot wire the fans with switches on the dash. Do that if you don’t want to fix the problem properly. Meaning by someone else who knows what to do. I noticed you did not say fan switch so PCM seems like the gremlin here. I don’t know that myself but it seems that one person at least thinks so. That’s why I mentioned the wire it direct (kinda dumb) solution. I would tell you why my 83 Camry got wired but it’s too long of a story and you don’t have that car anyway.

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The only switches involved are the relays and the OP replaced them, these are rarely the problem on this car.

That subject line is begging for a good reply;

Get married

run for office

take over for Carolyn for a while

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update for anyone having this problem in the future. it was the radiator cap. even though it was replaced a year ago, it failed. like Nevada_545 said the car overheated because there wasn’t pressure in the system. thanks to all that gave advise

@weekend_warrior1 Do you race an IMCA modified?

Aftermarket cap or one from Dodge (OEM)?
In the long run it pays to avoid most aftermarket parts.

:fireworks: Ding, Ding, Ding! We have a winner! :fireworks:[quote=“Nevada_545, post:5, topic:102393”]
The temperature reaches 250 F? If the cooling system cap is left off for refilling the cooling system, the coolant will boil before the fans turn on.

Congratulations to @Nevada_545 !
Once again you’ve given extremely valuable advice!

Your gift will be sent to you the second Tuesday of this week! :gift:
CSA :smirk:

P.S. Please keep contributing. Don’t go anywhere. One of these days I’ll need some help!