Corolla radiator fan switch: Parts Store confusion about number of connector pins

My early 90’s Corolla radiator fan switch in on the fritz. It’s what turns the radiator fan on and off, according to coolant temp.

This gadget sort of looks like a meat thermometer and screws into the engine in the area where the hose from the bottom of the radiator feeds into the engine coolant intake. See a photo below.

It screws in just underneath the distributor. Its long axis is oriented the same as the long axis of the car. (There are two other coolant sensors that screw into the engine, one for the ECM, and one for the dash gauge, but they are oriented 90 degrees from the temp switch, i.e. with the short axis of the car.)

The problem is the parts store replacement version has only one pin in the connector, while the one original to the car has two pins in the connector. In The thread size and length is the same, and the connector configuration is the same, just that one pin is missing. The switch action is to ground, and in the original one the ground is provided by the second wire. I’m thinking on the new one the ground is provided through the switch to the engine ground, making the second pin unnecessary.

The corresponding connector on the car has one black wire (for ground), and one light green wire (for the switch) if that is of any help.

Has anyone here had this same problem? I’ve looked on Rock Auto and AutoZone websites, and as far as I can see, they only have the single pin versions. Any ideas?

I would go to a Toyota dealer and see what theirs looks like.

You need to take a meter and check if the circuitry in the switch is isolated from the body of the switch or if supplies a ground. If there’s no ground between the circuitry and the body then you need the two terminal switch. If there is a ground, then the one terminal switch will work.


@oldtimer11 … I tried Toyota too. They had a hard time differentiating with their computer database between the fan coolant temp switch and the ECM coolant temp sensor. The latter is a thermistor, not a switch, and screws in a completely different location and orientation. They had the temp sensor they showed me, but I could tell that isn’t he part as the threaded portion is much smaller diameter. They didn’t have the part they thought might be the switch in stock so I couldn’t inspect it. Also the Toyota price was $150, while the parts store is $22. Gives me incentive to use the parts store.

Thanks @Testr … I had this idea too, and asked the parts store if they had a DVM I could borrow, but they didn’t. I guess if I owned a parts store, I’d have inexpensive measuring gadgets like this on hand for the customers to use to verify the part is correct, but maybe the customers would steal the DVM’s and me, thinking they wouldn’t, that is why I don’t own a parts store … lol … Anyway, following your suggestion, I’ll go back to the parts store tomorrow w/my own DVM. I expect from doing further investigation that for the replacement part for this application, the vendors have experimented and find it works fine without the second pin, so they dropped it to save money. And other models & years may not use this second pin in the OEM part, so it allows the replacement part to work for those models too.

No George! Test your switch FIRST!

You need to know if the cicuitry is isolated from the body on the ORIGINAL SWITCH!


@Tester … good idea, I’ll do that test. But it seems to me it wouldn’t matter whether the existing switch ground is isolated or not from the body. As long as the new one switches the single pin to the switch body at the correct temp, as long as the switch is screwed in, it should work shouldn’t it?

I have known the parts catalog to be wrong on occasion. What makes it interesting is to talk to parts counter people who believe the computer is infallible. Makes for a very funny conversation.

Looking at the image of the connector end, it appears they simply deleted the one pin from the switch. The connector is keyed so that the signal pin will always mate to the appropriate wire in your two terminal harness connector. The “ground” wire is not needed with the later designed switch. What has likely happened is that in a later year revision, they omitted the extra expense of the ground wire from the harness and revised the switch design to use a common ground through the metal base of the switch. They then obsoleted the original version of the switch.

The cooling fan switch has one pin and is located in the radiator according to Auto Zone

The coolant temperature sensor that connects to the computer is in the engine

The pin connectors can be viewed for the parts. A single pin is on the fan switch and 2 pins on the sensor.

Ok, this is what I’ve learned so far about the early 92 Corolla radiator fan switch.

What I thought was the coolant fan switch, wasn’t. That part appears to be the cold start injector timer, which is in fact a switch of sorts affected by coolant temperature. It is a two pin job, and installs in the thermostat housing. It has thermal contacts which switch at a certain temperature. I could measure the resistance change abruptly when it switched as the temp increased, which is partly what confused me identifying the correct part. But it has nothing to do with the fan.

The coolant switch which controls the fan is very close to the one above. It’s not in the radiator @RodKnox , it’s in the housing where the lower radiator return hose connects to the engine. Its connector only has one pin.

Unfortunately for me, another part of the confusion was that both of the associated connectors to those two parts use green wires, so when I found one with a green wire, near the location where I thought it would be, I thought that was the likely candidate. Nadda.

Thanks to all for comments. I’ll fill in the results here when the job is finished.

AutoZone should (or not) have these kind of things sorted out in their computer database. Not everything they show is correct even if they think otherwise.

I’ve gone round and round a few times with them over exactly what constitutes a tie rod as compared to a tie rod end. Two completely different parts and most of the time they have them listed with the same description; tie rod.

Like all web sources Auto Zone has its limitations, but it is the most accessible and complete site that I have found to investigate questions such as this. The manufacturer’s photographs and description are usually quite informative.

Job done. If everything had gone smoothly, it would have taken about 2 hours. Instead, it took 6. I plead my mea culpas here for everybody to see! It was me! I was to blame.

Seriously, I was – well, my unscientific stubbornness I guess – was for the most part responsible for the extra 4 hours. Here’s what happened: I studied the shop manual in my office prior to doing the job, and was certain that the part I saw on the car in the garage was the same as the part on the drawing I saw in the office – green wire and all. If I had brought the shop manual out and looked at it while at the same time looking at the car, I’d have noticed that it was actually the part screwed into the water jacket two inches to the right that was the fan coolant temp switch. Ok, lesson learned. Fewer assumptions going forward.

The shop manual contributed its part to the confusion also. It is divided into sections: Engine mechanical, engine cooling, engine fuel, engine emissions, etc. There are four gadgets screwed into the engine’s cooling jacket: the fan switch, the cold start timer, the dash gauge sender, and the coolant temp sensor for the ECM. What I needed was a good drawing showing where they all are located w/respect to each other. But this is all that is all that is provided in the shop manual. See the picture attached.

The “radiator fan coolant sensor switch” is in the cooling section, but the “cold start injector coolant sensor timer” – which looks very similar to the radiator fan switch and is also screwed into the cooling system – is located in the fuel system part of the shop manual. Likewise the coolant temp sensor for the ECM is located in the emissions section of the shop manual. And there is no drawing showing both of them in the same drawing. There’s no drawing at all showing exactly where the cold start timer is located, just a verbal description of “in the area of the thermostat housing”. But that’s where the fan switch is too.

Lack of the exact tool was another problem. If I had had a 22 mm deep socket, I could have avoided a knuckle busting parts removal procedure. Instead, I had to so it with a combo wrench. No fun. And time consuming.

Finally, the retail parts stores contributed some confusion as well. When I asked for a “coolant temperature switch for the fan”, their computer brought up several different parts matching that description. Each parts store computer was different – just to add to the confusion – but all the descriptions were ambiguous, and looked like this:

  • Engine - Coolant Temperature Sensor/Switch
  • Coolant Temperature Sensor/Switch (For Computer)
  • Coolant Temperature Sensor / Switch
  • Coolant Temperature Sensor Sender
  • Air Conditioning Switch

So the parts store employees were not certain which part I needed either. And since I was sure what it looked like, well, you get the picture where the extra 4 hours went … lol …

Hope this all wasn’t too boring but it is an example of why a professional mechanic, with all the experience they get on the job daily, can get a job like this done 3 or 4 times as fast as a driveway amateur. But its not stopping this particular driveway amateur. Job done, car is back on the road. Radiator fan purring like a kitten at 195 degrees F.

P.S. As if to make my job as difficult as possible, even when I finally got hold the correct part, on the box it came in, was it labeled “radiator fan temp switch 195/185 deg F, 12 mm”? No, it was labeled “DC Temp Sensor Commutator”!!