Finally got around to replacing the coolant sensor (in the WP) today. I wasn't able to get it in quick enough, and ended up loosing about a liter of coolant in the process. I tried just refilling it through the radiator fill, but I think I ended up with a decent air pocket somewhere (kept gushing out of the radiator). Shut it off, let it cool a bit, cracked both bleeders, and filled it again until I got a steady stream of coolant out of the WP bleeder, and closed that one. Continued filling until I got coolant from the other, and closed that one. Capped the radiator, and filled the overflow to halfway between cold and hot full. Let it idle in the drive for a while, and noticed the fan never came on. Shut it off when the temp gauge hit the last major line before the red.

I had no cooling problems before I changed the sensor, so I really doubt the the WP is bad, or that I have a blown head gasket. I also saw coolant pumping through the radiator, so I know the WP is pumping.

The PO told me the primary fan motor is bad, and disconnected it. He also moved the connector from the primary to the secondary fan, leaving the connector that would have gone to the secondary disconnected.

I was looking at the wiring diagrams on Shoebox's site, and it looks like it should work OK in this configuration, from a wiring standpoint. Obviously it won't give me maximum cooling ability. I've confirmed the relays are good, and the fan does come on when the AC is on, or when the ALDL is jumpered to pull codes. All fuses are good, both in the dash box and underhood box. I've pulled the ECM BAT fuse for a few minutes to reset the ECM as well.

I'm building a ALDL cable tonight to check out what the ECM is reading from the coolant sensor.

Do both fans need to be connected for the auto operation to work correctly? Assuming the ECM is getting correct readings from the coolant sensor, is there anything else I should be checking before blaming a faulty ECM?

 

If the secondary fan comes on when wired with the primary harness, but primary fan does not come on with the primary harness, then it sounds like the fan motor.

 

I haven't yet tried switching the connectors back over, mainly because I don't have a jack here at my apartment (anything beyond basic hand tools is still in my garage in Michigan ), and my fat *** is too big to slide under the car .

Right now, the secondary fan isn't coming on at all unless I turn the AC on or pull codes. Checking and/or replacing the primary fan is at the top of my to-do list for the car, but right now I'm more just wondering if I need that fan in the circuit for the ECM to command them on (and trying to track down the "problem" will be a waste of time without a working primary fan), or if I'm going to have the same problem after replacing the fan.

If it turns out to be ECM related, I'll probably just add in an external fan controller.

 

Easy to check the primary fan; just apply 12V directly to the connector.

 

Having the fan unplugged should not bother the ECM commanding them on. Any monitoring the ECM is doing, stops at the relays.

 

Thanks shoebox, that helps a lot I'll have more info later when I wire up the aldl cable.

 

Finally got around to getting the cable done (turned out that the two transistor schematic floating around isn't 100% correct, it needed a jumper on pins 1,4,6, and another on 7,8), and hooked up in the car.

I used the TTS Datamaster, and let the car idle in the parking lot up to 230 degrees, cooling fan never came on. It does come on when pulling codes via paper clip method, and does come on when the AC is turned on. The car has been sitting for several days now, and the initial engine temp reading was around 95 degrees, which is slightly higher than ambient at the moment (around 80 degrees). It rose about the same as the in dash gauge.

At this point, it looks as if the ECM may have "issues". I'm thinking about just picking up an automatic fan controller from Summit.