1998 Toyota Tacoma Location of temperature sensor?

Hi Chad, sorry for the delay in replying and thak you for the donation.

The switch in front is fan switch and is for the cooling fans, it would not show any codes.

The switch at rear of engine is the ECT and that would cause the trouble code.

What is the trouble code that you are getting?

It shows- closed loop fuel control, insufficient coolant temperature.
I think it's PO-0125
Thanks again!

Update- I changed the coolant temp sensor at the back of the engine (with some difficulty) Reset the codes and drove around the bolck. The code came back again...not sure what's next to check.

I believe you have got the wrong sensor. The code is for the Heated O2 sensor. Here are the diagnostic procedures.

Thank you for the replies. I have tried to measure the voltage of the oxygen sensor like you suggested but I am not familiar with this function on the scanner.

I'm using the Actron Autoscanner plus model CP9180. I found an option under vehicle diagnostics that shows the RPM of the vehicle along with temperature etc. There is one line that says O2S1 v- I am guessing that's the one that monitors the voltage of the O2 sensor #1...? I snapped the throttle up to 4K RPM's 3 times and the O2 sensor #2 went up to the 0.800-0.900 range while the O2S1 hardly changed at all.

I think we're very close to solving the problem (thanks to your help) but there are 2 oxygen sensors and they are $125 each. I really need to know for sure before I purchase one of the sensors.

Thanks again fellas!

I dont kn oe where KWLow2008 is but he is the local forien guy, But thr upstream 02 is supposed to switch frequently whereas the down dtrem 02 should remain fairly constant, so these are normal.

Merlin, thanks for helping out.

If the reading of the # 1 sensor is hardly moving, then it should be faulty as it is the upstream sensor, the one before the catalytic converter. You reading are opposite of what Merlin pointed out, as if the sensor circuits had been reversely installed.

Reconfirm the readings.

The sensor before the catyltic converter reads about 0.005- almost no fluctuation, goes up to 0.015 at high RPM...while the one after the cat reads anywhere from 0.025 to 0.975

I tried changing it but the nuts were so rusty they crumbled in my hands. Got to have new threaded studs welded on and hopefully get the O2 sensor replaced tomorrow.

Yes, that seems to indicate the front sensor is bad.

These sensors are notorious for causing trouble and I usually try to remove them when the temperature is hot. Risk getting scalded but it has a higher percentage of getting the job done without any trouble. A little spray of rust penetrants does helps.

Good luck.