1996 850 Low speed radiator fan not turning on [Bad ECT sensor] Topic is solved

[abscate]

It sounds like it just defaults to "I don't know the temperature so lets turn the fan on high to cool the motor just in case its hot"

[ZionXIX]

It sounds like it just defaults to "I don't know the temperature so lets turn the fan on high to cool the motor just in case its hot"

I wish that was happening. As long as the infinitely resistive sensor is plugged in, the ecu reports a temperature and the fan does not come on. If I unplug it, it runs the fan on high in case of overheating. Anyways the part should be here soon and then we can see of it works.

[Chuck W]

Also check your AC high pressure switch. It's what allows the ECU to signal the low speed fan to turn on.

Still not sure why using the app didn't trigger the fans. It's independent of all of the sensors/switches.
Did they even act like they triggered at all? It doesn't turn them on to run, it just pings the relay, and all you hear is a quick engagement for just a second.

[ZionXIX]

Also check your AC high pressure switch. It's what allows the ECU to signal the low speed fan to turn on.

Still not sure why using the app didn't trigger the fans. It's independent of all of the sensors/switches.
Did they even act like they triggered at all? It doesn't turn them on to run, it just pings the relay, and all you hear is a quick engagement for just a second.

My AC is working. Does that suggest a functioning high pressure switch?

I was expecting a quick turn of the fan, should I be listening for the relay to click?

Am I just checking the AC high pressure switch for corrosion or is there an ohm value I need to check too?

[Chuck W]

My AC is working. Does that suggest a functioning high pressure switch?

I was expecting a quick turn of the fan, should I be listening for the relay to click?

Am I just checking the AC high pressure switch for corrosion or is there an ohm value I need to check too?

Nope. The switch was bad on the wife's car. The high speed fan would come on when the car got hot enough, but it wouldn't kick on when the pressure on the high side of the AC system got high. The AC worked just fine, aside from that. The switch sends a signal to the ECU when the pressure in the system gets over 3 bar.
Someone posted a pinout of the switch, but I can't remember the thread, It's a 3-pin switch. power, ground, signal.

Basically all I heard with the test was a loud click of the relay trying to start the fan, then just stop. You will not hear the fan run.

If you retest with the app, and the relay signals are good, it's most likely the high pressure switch.

[ZionXIX]

Today is the day people!
I changed the coolant temp sensor and what an incredible difference.

My old sensor would read about 206F when the coolant was expanded to the top of the reservoir and then begin seeping out at 208F.

The new sensor reads 208F and the coolant is barely expanded above the the MAX line. At 215F the coolant was only up to the middle of the word "MAX" on the reservoir. At 217F the low speed fan kicked on!

This information leads me to believe the coolant was running much much hotter before when it was at the reservoir cap. I think I will sleep better not knowing.

Anyway problem is fixed. I did not have to replace the high pressure AC sensor switch luckily. That thing is expensive. Of course if I have cooling fan problems in the future I might replace that next.

[abscate]

Anyway problem is fixed. I did not have to replace the high pressure AC sensor switch luckily. That thing is expensive.

Very cheap and highly reliable PnP part - never buy new.

I harvested a couple from my parts cars, check part number if anyone ever needs one.

[Chuck W]

I'm pretty sure the low speed fan is supposed to turn on with the AC (when required) and the high speed with the engine temp.

If you get NO (low speed) cooling fan when the engine isn't "hot" and the AC has been turned on, your high pressure switch is most likely bad. (This assumes that you have a good Freon charge in the system)

[ZionXIX]

Anyway problem is fixed. I did not have to replace the high pressure AC sensor switch luckily. That thing is expensive.

Very cheap and highly reliable PnP part - never buy new.

I harvested a couple from my parts cars, check part number if anyone ever needs one.

I like new shiny parts and the lifetime warranty though, and as far as reliability my sample is 1 so I haven't experienced the reliability factor.