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Auxiliary fan issues

H

hightime81

NAXJA Forum User
Location
Holly Springs, NC
Hi All!
actually asking this question for a buddy's 2000 sport, 4.0HO, AW4, with 150K

his auxiliary fan NEVER works (not due to temp or AC/defroster) lol, i jumped it with the battery and it came on, so is this a ground issue i need to trace down or could the coolant temp sensor be failing?



And for my 93' sport, 4.0HO, AW4 with 120K - Mine comes on with AC/defrost but never when the temp creeps up to 210. However, if i park it after a 30min drive to run into a store and then turn it back on, the temp gauge shows 220-240 or so and the fan comes on as soon as the engine is finished cranking, and runs until it drops back to under 210... coolant sensor failure?

sorry for the twofer here... figured 2 birds, one stone!

Thanks all!
 
The fan should come on at approximately 218*, so no worries on question #2.

As for the first question, if niether temp nor A/C turns your friend's fan on, I believe that would rule out sensor issues. I would first check the 40amp Radiator Fan fuse located in the PDC to make sure it is OK. If that checks out, check the Radiator Fan Relay for proper operation, also in the PDC. If that checks out, then yes, start checking your fan wiring for bad connections.
 
fyrfytr1717 said:
The fan should come on at approximately 218*, so no worries on question #2.

As for the first question, if niether temp nor A/C turns your friend's fan on, I believe that would rule out sensor issues. I would first check the 40amp Radiator Fan fuse located in the PDC to make sure it is OK. If that checks out, check the Radiator Fan Relay for proper operation, also in the PDC. If that checks out, then yes, start checking your fan wiring for bad connections.
Click to expand...

For #2: My FSM says an auxiliary electric fan operates whenever engine
temperature exceeds 190 or air conditioner is on.

that is why im thinking coolant temp sensor.. it might be smart for me to verify temps as well externally (infrared).

for #1 - i already tried replacing the relay with mine to see if that was it.. so i guess its time for the hunt! (or to bypass and put a switch in cabin:))

thanks!
 
Last edited:
2000 and 2001 the e-fan ONLY comes on when temps exceed about 218*. Test the fan by applying 12 volts. Check the relay, wires, and test or replace the coolant temp sensor.
 
Tim_MN said:
2000 and 2001 the e-fan ONLY comes on when temps exceed about 218*. Test the fan by applying 12 volts. Check the relay, wires, and test or replace the coolant temp sensor.
Click to expand...

Ok, well that makes a difference! so even with defrost or AC on, the E-fan won't kick on until the temp exceeds 218. That is VERY helpful! i will have to test the temps coming out to see if the Coolant temp sensor is accurate.

The fan does work when i jump it to the battery.

thanks again!
 
Tim_MN said:
2000 and 2001 the e-fan ONLY comes on when temps exceed about 218*.
Click to expand...

Are you sure? I figured 97-01 were the same in this regard:

1999 FSM said:
When coolant temperature reaches approximately 103°C (218°F), or when air conditioning is requested, the powertrain control module (PCM) provides a ground path for the fan relay. This ground is provided to the cooling fan relay through pin C2 of PCM connector C3. Battery voltage is then applied to the fan through the relay. When coolant temperature drops below approximately 98°C (209°F), the PCM opens the ground path to the relay. This will prevent the cooling fan from being energized.​
Click to expand...

Then again, maybe 00-01 are different. :dunno:

hightime81 said:
for #1 - i already tried replacing the relay with mine to see if that was it.. so i guess its time for the hunt! (or to bypass and put a switch in cabin:))

thanks!
Click to expand...

Did you check the 40amp radiator fan fuse in the PDC? How about the 15amp fuse for the fan relay in the junction block (should be slot #10)?
 
2000 4.0 4WD automatic all stock.

OK, Tim_MN, so the 00-01 are different. How do they work? Furthermore, how do I go about figuring out why my electric cooling fan doesn't work? I've straight wired it to the battery and it will run, but it doesn't come on with the AC or when the temperature goes well above 218 on the gauge. Thanks for any help.
 
Well, maybe I can help.

00-01 the fan no longer runs automatically with the a/c compressor.

The aux fan in 00-01 is strictly controlled by the PCM, based on data provided by the CTS.

I don't have the specs for the 00-01, but I believe the fan start is somewhere around 217 degrees or higher. Maybe someone with an 00 or 01 FSM will pipe in.
 
Some time it's the fan Relay, it square with 3 prongs on it, I replaced mine but can't remember exactly where it was, It might be in the other fuse box under the hood. I also remember reading somewhere here if your refrigerant is low it could effect your auxiliary fans operation.
 
The 2000 is basically the same I think the temps are a little higher though. The PCM does control it but like was stated will only come on if the engine temp reaches threshold (through CTS) or the a/c is pressure reached a certain threshold as well.
 
Ok I checked my 2000 XJ FSM. "Fan is controlled by cooling fan relay in PDC. Relay is protected by 15 amp fuse in junction box. Fan is protected by 40 amp fuse in PDC. Fan will come on at 223*F and go off at 217*F. Regardless of coolant temp, when a/c system pressure reaches 300psi fan will engage and stay on till pressure drops to 235psi". That's what the books says.

I would verify that the fan is good (resistance test across the fan) and that it's is in fact getting power & ground when it's supposed to (hot engine or a/c on). My moneys on the CTS though. If you disconnect the connector from it the fan should come on right away if not the sensor is most likely bad.
 
Last edited:
2000 4.0 4WD automatic all stock - 144k miles

Thanks, robsjeepxj. I try the CTS check you describe tonight.

Am I correct that the CTS is tapped into the block at the front above the water pump on my 2000? Haynes Manual says "at the rear of the block", but I don't see anything back there.

By the way, I've checked all the fuses. Is there a way to check the relay, or do you just get a new one?
 
Last edited:
Yeah, (gotta love the Haynes/Chilton) in the thermostat housing at the front of the engine.

Dumb A** Haynes, the only "at the rear of the block" was the temperature gauge/idiot light sender that was actually in the rear of the head, driver's side on earlier 4.0s. On these earlier 4.0s the CTS--coolant temperature sensor--that sends data to the ECU is in the block, driver's side of the engine, under the manifolds.
 
Joe, not a big deal, but for others trying to sort through this, on some years such as my '93, the gauge sender is on the driver's side rear of the head and the CTS for the ECU is in the thermostat housing.
 
Pelican said:
Joe, not a big deal, but for others trying to sort through this, on some years such as my '93, the gauge sender is on the driver's side rear of the head and the CTS for the ECU is in the thermostat housing.
Click to expand...

Hence the "earlier". Do you remember what year the temperature gauge/idiot light sender was incorporated into the CTS in the thermostat housing--thinking OBDII so 96 or 97?
 
Thanks, Joe. Unplugging the CTS causes the fan to come on. Plugging it back in, causes the fan to go off. Must be the CTS, right? I'm fixin' to go to the parts store and get one to find out!
 
Yeah, when you unplug the CTS it triggers the fan, like a fail safe.

Good luck.
 
The CTS just provides temperature data to the ECM, which in turn controls the fan relay. By unplugging the CTS and seeing the fan come on, you've proven that the ECM is able to trigger the fan. So the control part works, and what you are left with is wondering if the inputs are there. The fan should come on when gauge needle is about halfway between 210 and the 3/4 hash marks. Also they changed the A/C trigger in 2000, so the fan no longer comes on with the compressor.
 
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