My ECM temperature sensor is reading cold. I want to replace it but wondering which one is the correct one. I read that some have smaller threads and need adapter bushings to screw into the thermostat housing. Which of these do I need? I've got an 85 duke auto w/AC.

AC Delco 2134396 vs 1551107 - these are for sale at rockauto and not sure of the differences. Many thanks.

AutoZone lists the following. No adapter is required. The V6 has a reducer/adapter that screws into the end of the lower intake and the ECM temp sensor screws into that reducer, but not for the Duke.


IT FITS. This product is a fit for your: 1985 Pontiac Fiero 2.5L TBI OHV 4cyl
Part Number: SU109
Alternate Part Number: PT3378
Warranty: Limited Lifetime

Thanks, but for shipping cost purposes I can only do rockauto on this one and they don't carry the number you gave. Does a Delphi TS10075 sound good too?

[This message has been edited by cebix (edited 11-13-2019).]

Looking at the Rock Auto site, that is a unit that should work. Direct fit. No adapter. No harness splicing required. Any of the sensors on that page that have an oval head on them will work.

Cool, thanks. Last question - any brand preferred amongst you guys? Is Delphi good or should I go Delco?

quote Originally posted by cebix: Is Delphi good or should I go Delco?

likely they both come out of the same Chinese factory.....

Guess there are no known quality alternatives?

New ECM sensor needs New Plug.
You must install a new plug if you have OE sensor and plug.
Plug should be Soldered to old wiring or likely will have problems down the road.
(87 and up have the new type as OE and shouldn't need new plug unless damage.)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

There seems to be a problem with buying and shipping a new plug. Can anyone tell me from these photos do I have the new plug already or is it still OEM?

The only alternative I have is buying an NTK sensor which comes with the plug and wiring. All other sensors come just by themselves.

[This message has been edited by cebix (edited 11-14-2019).]

quote Originally posted by cebix: My ECM temperature sensor is reading cold.

I'm just curious... how are you establishing that?

quote Originally posted by Patrick: I'm just curious... how are you establishing that?

Measured its resistance vs the temperature-resistance chart posted here somewhere and it was higher. I believe that is causing probably my lower mileage and cold start flooding issue. I guess my cooling system has a lot of issues.

A few years ago this sensor failed on me and my car was bogging badly and stalling even. I couldn't pinpoint the issue until it decided to throw a code 15 after a few days. Then I measured it and it was way higher than the chart said it should be. Now this replaced sensor also reads a little higher resistance but not that much.

[This message has been edited by cebix (edited 11-14-2019).]

To determine if you have the correct plug/sensor matchup, you can click on the item you choose, then the INFO button. In the upper left of that is an arrow. Click on that and you can get different views of the sensor, to include looking down into the plug area. You can see the shape that should conform to your harness end. All of them are oval where the weatherpak seal is, but inside may be shaped a little differently. The inside is the determining part.

You have the new plug but has damage plastic and maybe damage "pins" inside getting iffy reading.
This is a Metri-Pack "Pull to Seat" type and often not easy to fix or take apart. Is why many sell only pigtails you splice the whole thing. See my Cave, Weater/Metri Pack notes and Wire Service
Again new plugs need solder splicing or can cause fake readings. So Check the splices likely near that plug.

⚠️ Many online sources have wrong info including some post here for ECT sensor.
Correct Ω chart... See my Cave, Sensors Quick Ref
that data came from Fiero FSM.

I would scan ECM to read ECT to see if it matches coolant temp. That tests the sensor are all wires to it.
If have Cheap IR or whatever to watch Tstat tube is easy but many are not very accurate so only take their # with ± 1 - 3° at best.
If needed take out sensor and dip end you can measure easy like candy/meat/etc thermometer and water when at "room temp" then heat up to 50 to 80°C
Either way, If ECM see close to same numbers then likely Not sensor problem.
Because most "bad" sensors and iffy wiring read way off like thermometer in coolant/water say 30°C but ECM reports ECT in same water sees 0°C/32°F to even colder.