1993 Hydraulic Fan Motor...

[RodMillenFan]

I have responded recently to a discussion regarding a Gen3 V6 with a hydraulic fan motor, basically because I'm having problems myself and I've learned some stuff after digging into it. But now I'm stumped with my own problem and wondering what y'all might be able to share. First some background...

Our 93 SE V6 overheated (well, almost, not seriously) awhile back due to a water pump leak and low coolant. We've been kinda paranoid about the motor overheating since then, and it's been backed by the tendency for the car's cooling fan to rev LOUDLY after driving for awhile. The water temp (on the gauge cluster) sat right where it belongs, but I wasn't sure if that was because the fan was working so hard to keep things cool. Anyway, I decided to spend some time digging into the ECU recently to learn more. Here's what I've found:

1. The ECU, located behind the glovebox, has 9 wires leading to it comprising:
   1. Wire from "igniter" (black)
   2. Wire to ground (brown)
   3. Water temperature + lead (blue w/ white stripe)
   4. Water temperature - lead (blue w/ yellow stripe)
   5. Input lead from engine and ECT ECU (blue)
   6. Input lead from A/C high pressure switch (blue w/ red stripe)
   7. Input lead from ignition block (white w/ red stripe)
   8. Solenoid + lead (yellow)
   9. Solenoid - lead (yellow w/ blue stripe)
2. I hooked up a meter to leads 7 and 8 and drove around, listening for the fan motor and watching the voltage. I was wondering whether the solenoid was sticking open, and if I heard the fan going while the output voltage was low, this would indicate it. It turns out the solenoid was following instructions well-- while driving, this voltage would hover between 0 and 4V, but then climb to 6-8V after awhile... that's when things got loud. Incidentally, when jumping E1 and OP1 in the diagnostic terminal block, this voltage only climbs to 4V.
3. I hooked a separate mater to leads 3 and 4 while driving around to see if there was a separate signal (from the one that displays on the gauge cluster) for water temp which might be making the fan go nuts. After getting underway, the voltage across 3 and 4 stayed steady right below 2V. The output was flying high, and this never moved, so the fan ECU is not responding (as far as I can tell) to high water temp.
4. I hooked a meter across leads 6 and 2 (A/C overpressure) to see if this played a role. It was hard to get a reading (cheap meter), but it struck me as possibly a problem. Rather than fuss with it, I just unplugged the A/C pressure switch and jumpered it. The ECU could not get a "bad" over overpressure input this way. I drove around again and the fan didn't go quite as high, though it was still responding to changes in driving conditions. This is the most "normal" the fan sounded in awhile, so maybe this is the problem.
5. Still puzzled what signal the ECU is responding to in order to switch the fan on and off, I placed a meter across leads 5 and 2 (ECT) and it is basically an "idle" sensor. Foot off the accelerator and it's a steady 0V. Touch that pedal, even slightly, even look at it too closely and the signal goes straight to 12V. There is no linearity with respect to engine speed, load, or anything. It's just sensing idle position. Clearly this isn't giving a signal.
6. As I'm typing this I looked at the wiring diagram in my Toyota manual (indispensible, that things is!) and see that I should check for signal across the leads 1 and 2 and maybe 7 and 2, just to see what they're showing.

Here's my curiosity at this point... Is the signal coming from lead 1 or maybe 7? Is the signal actually being sent as an AC voltage where my DC meter wouldn't show it... y'know, as a variable frequency signal? It seems like this would be prone to noise in non-shielded wires. Is the voltage coming in from the water temperature actually a very high-resolution signal, and the ECU responds to variations smaller than my meter is indicating (as in, the span is very tight)?

Gah! I'm really not sure why Toyota decided to use a hydraulic motor for this application, as it certainly adds another layer of complexity to the design, and another layer of potential failure. I'm going to check the other leads as mentioned above in item 6, and I'll post more shortly.

If anyone has further knowledge in this subject, please post your thoughts, eh?

Thanks...

[RodMillenFan]

Okay, I'm back. I put the meter across the other leads and here's what I see. The voltage across leads 7 and 2 is simply the system voltage... turn the key to the on position, it's 12V or so. Start the engine, it drops a bit from current draw, then the engine kicks in and it's back to 12V and a little higher.

I put the meter across leads 1 and 2 and it's also 12V, similar to what I read. Interestingly, though, I started hearing a faint high frequency popping noise. It was coming through the radio. Funny, because my meter isn't nice enough to read frequencies (it's a Radio Shack, not a Fluke), but my stereo has an AUX in cable that was sitting next to the leads, and it was no doubt picking up RF noise.

Anyway, I pushed the accelerator and the frequency of the noise went up with the engine speed, so this is indeed sending some form of a tach signal to the ECU box. I'm not sure how the ECU might use JUST the tach signal (without actual engine loading) to decide when to kick on the fan, but this seems to be the only option that makes since. Every other input to the ECU stays pretty stable, but the ECU output changes. The tach input is the only thing that varies.

Even if that's the case... what next? What's making the ECU drive the fan so hard? I don't get it.

My next step... do the same tests on my 92 SE V6 and see if they're similar. Maybe it's less about the voltage output, and more about a hydraulic regulator gone bad. Maybe 4V isn't supposed to calibrate to such a high fan output. Hmmm...

Thanks for enduring my stream of consciousness here. And again, if you have any input, let me know!

[Rob_0126]

by all means, keep pondering, if it's just a switch, and not the hydraulic motor or ps pump, then more power. I cant afford those mega buck parts.

Mine roars randomly and puts a small load on the engine when it does this. Curious what it is.

Robert

[jwciv]

now that we're into the warmer weather here in MA, my 1994 V6 Camry is giving me a nasty fan whirring noise once the engine is warmed up. Temp gauge on the dash never even reaches the 1/2 way point, so it certainly does not seem like the fan has to run that hard. At idle it is quite, but step on the gas and the noise kicks in, sounds like a jet airplane.
Common problem?

[csaxon]

If the fans are constantly running on high then check the Condenser Fan Control Amplifier located forward of the glove box.

[jwciv]

Originally Posted by csaxon

If the fans are constantly running on high then check the Condenser Fan Control Amplifier located forward of the glove box.

thanks for the reply. Fortunately, it is not constant, only when you step on the gas, sounds very similar to the OPs comments.