View Full Version : sensor mixup!

03-08-2008, 02:12 AM
I noticed two sensor in my car.
1. The coolant temp sensor, i took it out an tested it, works.
This Guy
http://img86.imageshack.us/img86/2511/wl2su109003hf8.th.jpg (http://img86.imageshack.us/my.php?image=wl2su109003hf8.jpg)
it takes the temp data to the ecm.
2. Temp switch had a spade termial on it dont know how to test.
This guy
http://img86.imageshack.us/img86/1591/wl2tu66003kw6.th.jpg (http://img86.imageshack.us/my.php?image=wl2tu66003kw6.jpg)
it turns on the dummy light if the engine gets too hot.

Now i went to autozone and discovred a new sensor.. the radiator fan switch. I looked all over my engine and could not find it.
This Guy
http://img86.imageshack.us/img86/9403/wl2sw500003bq9.th.jpg (http://img86.imageshack.us/my.php?image=wl2sw500003bq9.jpg)
it swittches the fan on when it gets too hot.

My questions are.
1. Why is three 3 sensor couldn't one do the job? Tell the ecm temp data,turn on the fan and dummy light if it over heats.
2. Where is the fan switch? i have an 88 ciera with the 2.5

03-08-2008, 04:14 PM
On certain cars, the ECM does control the fan and orevheat warning light, based on data from its sensor.

I know the 1989 and newer 3800 SFI cars use the ECM controlled fan and warning light.

Most FWD cars had ECM controlled fans since EFI was introduced. According to the diagram there is dark green/yellow wire from pin A21 on the ECM to the fan relay.

If your car has a warning light switch (as you stated) it can only be tested by heating it in an oil bath and monitoring the temperature at which it closes. IF you have the equipment to do this test. If not, just replace it and be safe.

The car's circuit can be tested by grounding out the wire and seeing if the light illuminates.

03-08-2008, 05:03 PM
Temp switch had a spade termial on it dont know how to test.

Ground it out, the single wire...

1987 Shop manual says fan is controlled via computer "grounding" a relay.

03-09-2008, 05:33 AM
I glanced at my car and found two sensors. The spade terminal switch mounted in the top of the head. It turns on the dummy light when it overheats.
The second sensor was mounted in the thermostat housing and is called the coolant temp sensor.
Now there is this mystery switch autozone had and i bought by accident. It is the sensor on the bottom in the picutres. It turns the fan on if it overheats. I cannot not find it on the motor and is not mentioned in the shop manaual.

03-09-2008, 12:29 PM
You DO NOT have that fan switch on your motor. The ECM is on control of the fan. Auto Zone sold you a part you don't need.

If the fan is not working, try grounding the dark green/yellow wire from pin A21 on the ECM. This will manually engage the fan relay.

03-09-2008, 12:50 PM
Ok. Here is a diagram that should explain this. There are 2 schematics. One shows the ECM and the other the remainder of the car.

The circled areas concern the cooling fan. It's very simple. There is one fuse, the relay and a wire to the ECM for controlling. Then on the power side there is a 1 fuse link, the relay and the fan motor.

Hope this helps you. These drawings are taken from the following page, bookmark this it is VERY useful.