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1998 Toyota Tacoma Location of temperature sensor?

Tiny
CHADLEY22
  • MEMBER
  • 1998 TOYOTA TACOMA
  • 4 CYL
  • 4WD
  • MANUAL
  • 130,000 MILES
My 98 Tacoma shows a code that indicates a faulty coolant temp sensor. I bought one to replace it with but can't locate the sensor on the motor. Where is this sensor located? A picture of the location would be great.

I think the sensor for the temp gauge is next to the thermostat, and it's working ok.

Thank you very much- Chad

UPDATE- I located two sensors. One is up towards the front of the engine next to where it looks like the thermostat is hidden. The other one is on the very back of the motor right against the firewall.

Now my question is- which one of these sensors would cause the check engine light to come on? The trouble code indicates 'closed loop fuel control, insufficient coolant tamperature'
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Saturday, June 27th, 2009 AT 8:27 PM

8 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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?
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Sunday, June 28th, 2009 AT 3:44 AM
Tiny
CHADLEY22
  • MEMBER
  • 4 POSTS
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.
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Sunday, June 28th, 2009 AT 7:26 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
I believe you have got the wrong sensor. The code is for the Heated O2 sensor.

Here are the diagnostic procedures.


https://www.2carpros.com/forum/automotive_pictures/192750_DTC0125_98Tacoma01a_1.jpg



https://www.2carpros.com/forum/automotive_pictures/192750_DTC0125_98Tacoma01b_1.jpg



https://www.2carpros.com/forum/automotive_pictures/192750_ScanTool98TacomaFig01_1.jpg

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Monday, June 29th, 2009 AT 11:40 AM
Tiny
CHADLEY22
  • MEMBER
  • 4 POSTS
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!
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Tuesday, June 30th, 2009 AT 6:31 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
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.
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Tuesday, June 30th, 2009 AT 11:16 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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.
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Wednesday, July 1st, 2009 AT 7:03 AM
Tiny
CHADLEY22
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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.
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Wednesday, July 1st, 2009 AT 8:14 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
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.
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Thursday, July 2nd, 2009 AT 12:40 PM

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