Ok, more data for Rat or Will....

I disconnected the battery for 10 minutes, then looked at the connection to the Coolant Sensor again. I see 4.75 volts across the terminals on the cable that connects to the Coolant Sensor. That tells me (I think) that the wires back to the PCM are ok, and that the PCM is at least trying to read the Coolant Sensor. But... when I short the lines back to the PCM (emulating a high temp condition... I think...), the fans still don't come on. Grrrr....... I gotta be missing something here.

-Roger

Remember me saying this:
"2> Coolant SENSOR sends the signal to the ECM to tell it when to turn the Electric Cooling Fans ON! The Coolant SENDER sends the signal to idiot/gauge.
3> The Coolant Level Sensor is the one in the RH tank of the Radiator. This sensor has nothing to do with the fans!
4> There is 2 Cooling Fan Relays in the Engine'* Compartments Fuse/Relay Block! (1 for each Fan).
5> There is also a Cooling Fan Resistor located on the LH fan shroud.
6> The Coolant SENSOR is located below the throttle body & screws into the intake manifold."
Well, I have not heard whether or not that you've checked the fan Resistor yet? *See #5* :?
As for the relays....on the 92/93 it shows them as bottom row, third & forth from the RH side! If so, both of them you should be identical!

Try swapping the relays with the horn relay, one at a time. I doubt it will make a difference, but it will at least rule it out. Your resistance reading is correct for 'cold'. JR is right, 77° is 2.8k. You should be reading about 177 ohms at 200+° when the fans come on. I'm not too sure about the resistor, though, because you say the fans work with the AC compressor running....unless the resistor is only in the loop for the low-speed circuit.....pulling out the trusty schematic.......OK, the Rat is right on. The resistor is only in the low-speed loop. Your AC comp causes them to come on in high speed. Check that resistor!

Ok.. sounds like the resistor check should be next.

Will, back to that schematic.... Do both of the fan relays have to enguage to run the fans (at high speed) when the AC is on? If so... it'* probably not a relay issue, no?

Thanks again...

-Roger

I would also suggest that at 160K miles there'* no telling what kind of shape your cooling system is in. You may have all kinds of blocked passages, gunk buildup, etc.

I would start by flushing your cooling system with any off-the-shelf product. Then refill with the proper mix of coolant and ADD A BOTTLE OF WATER WETTER. This stuff works miracles with cooling problems. If you can't find it in a local store search for it on the internet. About $10 or less for a bottle.

I'd throw in that 180 t-stat as well just for insurance.

As far as the fans not turning, I'd guess there'* either a bad sensor or bad wiring and the PCM has no idea how hot the motor is. Just a guess.

At your mileage, your throttle position sensor might be causing some of the stalling problems... Again, just a guess and something to check.

It'* good to see a bonnie with 160K soldiering on...

Wesbo

2 seperate relays, Roger. One for hi speed, one for low. The low speed relay has the following wires in it: Red, Brn, Grn, Blk/Red....this last wire goes to the resistor and fan on the lo-speed side!

So Will, according to that schematic of yours, the LH (Driver'* Side) Fan is the main low speed fan. While the RH (Passenger Side) Fan is the high speed secondary fan. But doesn't the LH fan come on at both Low & High speeds? In other words is it a 2 speed fan? The resistor is just for the low speed setting right? :?

According to my schematic, The driver'* side fan is only low speed. It comes on when the ECM t ells it too for coolant temp in the intake manifold. The Hi speed passenger side comes on with the AC (when the ECM tells it too), and that relay ALSO tells the low speed fan to come on if it isn't already!

Of course, I have a hokey schematic. I'd really like to get my hands on the factory service manuals for this dog.

Some more data... (this subject is growing some hair, isn't it!)

Will, I verified that the slow speed fan is on the driver'* side. There'* two resistors, in series. Each one measures about 0.6 ohms (very high wattage resistors). There'* a cable connector in the slow speed fan cable, maybe 3 inches from the fan. Three wires going up to the fan, through the connector... I theorize that one is ground, one goes to the resistors, and one is direct to the fan... ) I disconnected the fan itself from the cable, and measured resistance across the points on the connector. I see the fan at about 10-12 ohms. Also, switching the meter over to low voltage, I see the fan motor generates a small voltage when I turn the fan manually (this is good... tells me the fan brushes are ok).

Connecting everything back up... start the car, and turn the AC on. Both high and low speed fans are running. So... I'm not sure where this leaves me. :? It seems like the low speed fan is ok, wiring to the fan is ok, low speed fan relay must be ok...

Will, is the ECM in the loop, to flip the low speed fan relay, when the AC is on? In other words, does the AC switch on the dashboard signal the ECM, which signals the relay? or does the AC switch bypass the ECM, and flip the relay on it'* own?

If the ECM is in the loop, then I think I'm back to something between the Coolant Sensor and the ECM. How much logic could there be in the ECM to do the Coolant Sensor checking? Probably not much... but maybe the ECM is the issue... If it'* bad, shouldn't it throw a code?

Rat, how much do ECM'* cost? :(

Thanks guys...

-Roger

Remember when I said my schematic was hokey? My fans work like that too.....both on low or both on high. The command to turn them on in either mode comes from the ECM, but from different pins. I don't have my schematic here at work, so I can't tell you exactly which pins.....but I'm pretty sure about this. I've been looking at that schematic alot the last couple days! So to recap, high speed works, and lows speed doesn't?

I'd like you to do something without burning yourself, Roger. Take the sensor out of the intake manifold (below the TB), and immerse it in a bowl of boiling water straight from the microwave......with the ignition on, but the engine not running (you don't want to spew coolant all over the exhaust....it stinks when it burns). Let us know what happens.....both fans SHOULD come on low, even without the car running or the ignition on, but we'll see