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Discussion Starter · #1 ·
My 2001 Grand Cherokee w/ 4.7L V8 recently began overheating at idle or in stop and go traffic. When cruising above 35-40 mph, it seems to cool OK. I noticed that if air conditioner is on, or else when engine temp over 220 F or so, the fan spins, but only very slowly. I would suspect that under those conditions the fan should spin pretty rapidly.

Last season (for other reasons) I replaced the water pump, radiator, and thermostat, so I suspect they're OK.

Several questions:

I've read about issues and replacement of the hydraulic fan solenoid. If I disconnect the electrical connector from the solenoid and measure voltage across the 2 pins while engine idling, should I see voltage when the temperature reaches a certain point, or when the a.c. is on?
If I don't see voltage, can I assume it's a computer issue?
If I do see voltage, can I assume it's a solenoid issue?

Is the voltage to the solenoid either 0 V or 12 V, or is there a range of voltage that determines how much it opens?

Is it spinning slowly because the solenoid isn't completely closing and allows for the fluid to flow just a little? Can the solenoid just be removed and cleaned/lubed?

Many thanks for any replies!

Carl - Dallas TX
 

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Discussion Starter · #2 ·
Update re:Troubleshooting Hydraulic Fan Solenoid

I've read a multitude of threads about this and probed around a bunch on my GC and think I've answered some of my own questions. I can now understand how it's supposed to work. There's no electrical relay. It's all hydraulic. Figuring out if the solenoid is OK is pretty easy. The following is a rather simplistic explanation and may not be entirely accurate, but I think the concept is pretty close.

When the engine is running, power steering fluid is pumped towards the hydraulic fan, and there's a trickle of fluid going through it so it spins slowly. If a constant 12V is applied to the solenoid, it becomes completely energized (I don't know whether that means completely open or closed) and it diverts 100% of the fluid flow within the fan apparatus resulting in maximum fan speed. But depending upon different inputs into the computer (whether ac is on, different temperatures, etc.) it will decide whether to apply a constant 12V for full speed, or different pulse widths of 12V to the solenoid, causing it to energize only partially and divert only a portion of the flow resulting in intermediate fan speeds.

There is a 3 wire harness behind the top of the radiator. Only 2 of the wires (Blu/Rd and Or/Gn) actually go to the solenoid. The 3rd wire (the black one) looks like it's headed for the solenoid, but really connects to the frame of the fan as a ground. I pulled the connector loose behind the radiator and measured resistance between the Blu/Red and Or/Gn wires to the solenoid. I figured if it was a bad solenoid coil, those wires would show either open or shorted. I measured about 12 Ohms. So I figured it wouldn't hurt to apply 12V to those 2 wires. I wired it together with clip leads in series with a 1 Amp fuse (12V/12 Ohms = 1A) and, while the engine was running, applied 12V to the terminals in the connector corresponding to those 2 wires. The fan immediately spun at full rpm.

So even though it overheats at idle from low fan speed and I got code 1499, the solenoid doesn't need to be replaced.

This is fresh info and I haven't poked around yet to see why the solenoid doesn't seem to be receiving 12V from the module. But at least, I thought it may be helpful to pass along how easy it was to see if the solenoid is OK.

Carl - Dallas TX
 

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My 2001 Grand Cherokee w/ 4.7L V8 recently began overheating at idle or in stop and go traffic. When cruising above 35-40 mph, it seems to cool OK. I noticed that if air conditioner is on, or else when engine temp over 220 F or so, the fan spins, but only very slowly. I would suspect that under those conditions the fan should spin pretty rapidly.

Last season (for other reasons) I replaced the water pump, radiator, and thermostat, so I suspect they're OK.

Several questions:

I've read about issues and replacement of the hydraulic fan solenoid. If I disconnect the electrical connector from the solenoid and measure voltage across the 2 pins while engine idling, should I see voltage when the temperature reaches a certain point, or when the a.c. is on?
If I don't see voltage, can I assume it's a computer issue?
If I do see voltage, can I assume it's a solenoid issue?

Is the voltage to the solenoid either 0 V or 12 V, or is there a range of voltage that determines how much it opens?

Is it spinning slowly because the solenoid isn't completely closing and allows for the fluid to flow just a little? Can the solenoid just be removed and cleaned/lubed?

Many thanks for any replies!

Carl - Dallas TX
 

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I’ve read all the comments regarding problems obtaining replacement solenoids for the GC WJ and can’t help wondering why the replacement 3 pin version can’t be modified. Since the 3 pin connector only has the two powered wires and and a ground, the solution maybe to cut off the 3 pin connector and also the 2 pin from the faulty solenoid and solder the two powered wires to the 2 pin using the same configuration and grounding the ground wire (black) on another part of the motor.
This should avoid the need for finding a used fan assembly and allow the replacement version of the solenoid to be used on all WJ models 01 through 04
 
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