Tor the record, the ECM (or ECU, same thing) is generally referred to as the engine computer in most cars. It is in this discussion as well. I don't believe your ECU is bad and not turning on your condenser fan, it's certainly possible but I believe it's highly unlikely. Perhaps the shorted fan motor backfed thought he relay and damaged the ECU, but usually the fuse blows first. And it your case it seems like it did.

In these trucks the ECU, BCU, cluster, and key all need to be paired for the truck to function as designed. You can swap an ECU in to try it, I think what happens is your odometer starts blinking. I'm not sure what happens if you replace the original unit, IE, does it automatically re-pair. If you want a loaner ECU send me a PM. Or if you want to buy a full compliment of computers and keys, I think that's a little extreme however.

I will add this, last night the ambient temp was 78°, I started the truck and turned on the AC and for the first time in my memory, the AC blew cold and the condenser fan did not run. Obviously it's probably happened in the past and I just didn't notice. I still think you should drive the truck a bit and see if the fan comes on in the right conditions (assuming you haven't).

 

The fan does not come on right away. I tested this last time I tried to help. It takes about 5 minutes and it was 25 degrees Celsius outside.

im not sure how it knows to come on. Pressure sensor somewhere I don’t know.

 

I'm sure differing conditions affect the fan operation. Mine has been coming on as soon as I start the truck(s) all summer so I'm certain "it can", I agree that it's not always the case however.

 

Thanks for all the help.

I did drive it around quite a bit.

AC was turned on the entire time and blowing cold.

The air temp was over 90F: It registered 92F on the ATC display.

Per my ODBII (Creader123) the engine coolant got up to 97.5C (averaged around 95C, moved between about 93 and 97.5) and the air temp was 60C.

Not sure what the air temp data stream from the ODBII is compared to the reading on the ATC display as they are quite different. I assume that the ATC is reading from the ambient air temp sensor in front of the condenser?

I really think I got it into states/conditions where the fan should have been energized by the ECM.

Bummer that the ECM needs to be paired to the vehicle.

What about the main relay, which seems to be in the same circuit as the condenser/engine fan relay? I have 12-14V on Pin 1 (or is it Pin 2?), which indicates to me that the relay control circuit has power and that the ECM just has to take whatever Pin it controls (1 or 2) to ground to energize the coil on the relay and allow current to flow to the condenser motor.

 

I believe air temp value in your ODB reader is from the MAF sensor and what the ECU is using to calculate O2 density in the intake. 60°C sounds about right.

I agree that you should have had a condenser fan running under those conditions. The ECU switches ground on Pin1, Pin2 is constant voltage whenever the key is in Position II. When the ECU provides ground at Pin1 the circuit is complete and the relay is energized. This passes voltage from Pin5 to Pin3, which then energizes the fan.

The main relay is energized whenever the key is in Position II. If this circuit had a problem you would have a multitude of other issues, as the main relay also powers the ECU.

It is sounding like you have a problem with your ECU providing ground at Pin1 of the fan relay when the fan is called for. I would try two things. Backprobe the ECU connector C0636 at Pin31 and make sure you have continuity between the ECU and Pin1 of the relay base to confirm the wiring isn't broken, and then check for the presence of ground at Pin31 when the ECU is calling for the condenser fan to run.

Edit, Here's a picture of the ECU connector, C0636. Pin31 will be a Green/White wire.

 

Thanks so much for all the help Ahab.

Pin2 of the condenser fan relay socket indeed had 12.7-14.1v on it (12 when engine off, 14 when alternator spinning).

Pin1 shows weird electrical behavior as I recall. It shows 5ish volts (which would be consistent with what I would expect to be the 3-5v range I would expect the ECM power bus to be at), then shows equally weird resistance measurements.

I'll test again this AM, as well as check out the continuity from relay socket Pin 2 to Pin 31 of connector 0636.

And the Pin 4 you refer to which should be a ground is also in C0636, right?

Lastly, what is the color code "BU" fior Pin 4 (B=black, U=?)

 

You can ignore the voltage seen at Pin1 of the relay base. That's transient voltage coming through the ECU at super low milliamps. It's truly a ground switch.

Regarding the BU wire at Pin4, I mistakenly referenced the TD5 schematic when I first posted, that uses a completely different pinout. That reference to Pin 4 is incorrect. I edited the post to include a new image of the correct connector but missed one old reference to Pin 4. You want to test for ground at Pin31 at connector C0636, and it's a Green/White wire. It looks like it's the middle connector at the ECU.
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1. Again, you should have continuity to ground at Pin31 at C0636 when the ECU is calling for the fan.
2. You should have continuity between Pin1 of the relay base in the engine compartment and Pin31 of ECU connector C0636 at all times.
3. You should not have continuity between Pin1 of the relay base and ground when the engine is off.

If #1 is true but #2 is false then you have a broken connection between the ECU and the relay base. If 3 is false then fan would run whenever the truck is running so this obviously isn't the case.

Apologies for the misinfo in Pin 4 but just for the hell of it here's the wiring legend.

 

Ok, finally got the operating temp above 97.5 C and success (maybe).

I finally got the coolant temp over 100C and the fan runs: hurray:

So I now know that the ECM pin that controls the condenser fan relay is not bad -- huge relief. (was going to do a continuity test but decided to drive one more time as air temp finally got to 95F).

However, not sure whether my ATC is functioning correctly as the wording of under what conditions the ATC sends a signal to to the ECM to engage the fan is still kinda ambiguous.

Back to the language from the RAV

While the A/C system is on, operation of the electric engine cooling fan, to assist refrigerant condenser operation, is
determined by a combination of vehicle speed and external air temperature. When cooling fan operation is required,
the ATC ECU outputs a cooling fan request to the ECM, which then energises the cooling fan relay. The cooling fan
request is output if vehicle speed is 80 km/h or less while the external air temperature is 28 °C (82 °F) or more.

So it the fan suppose to engage:

when the vehicle speed is 80 km/h or less while the external air temperature is 28 °C (82 °F) or more?

or

when the vehicle speed is 80 km/h or less while the external air temperature is 28 °C (82 °F) or more AND the engine (coolant) temp exceeds exceeds some temp ( threshold 100C)?

BTW, 2 questions related to this:

1. Can the backlight bulbs in the ATC be replaced (as a couple of mine are burned out. so maybe I need to replace the ATC anyway)?

2. What is supposed to be the (coolant) operating temp range of the engine -- mins and maxes?

 

Yes the bulbs can be replaced. There's a kit, it's about $40.

The operating range of the coolant is roughly between 170°F and 220°F. This is a bit subjective but that's about where you want to be. Under 200° is the general consensus of a safe place. Below 170° and you may get mixture-related codes, above 220° and you may get headgasket-related codes (haha). That's not to say the truck won't run outside of that range, but repeatedly staying outside of it isn't doing your truck any favors.

It does stand to reason that the ATC could be flakey. I'd run it for a few days and monitor the fan operation. It's 95°F outside ride now and when I started the truck cold and turned on the AC, the fan started immediately. I'm happy to ship you a loaner if you want to try a known good unit. I have to guess that they're pricey. I can even stock it with good bulbs if you find out yours is actually bad and want to buy it.

 

@austinlandroverbill I can confirm my the A/C extra fan comes on as soon as I start the AC. Outside temp at 30 deg C, AC set to low and Disco parked