Thermostat and O2 sensors

[John B Kobberstad]

1998 Plymouth Neon Highline Coup
2.0L DOHC MTX 129,000 miles

Had a P1281 code come up yesterday which means that the engine is not coming up to temperature (160 F) within 20 minutes and probable cause is the thermostat. The vehicle is being driven 75 miles to work and 75 miles back from work and doesn’t have good heat.
If the engine temp is not coming up can this cause the O2 sensors to not function properly, because the PCM is thinking that the engine is not up to proper temperature?
The STFT and LTFT were both at 24.8 with live data on scanner.

Topic

[EricTheCarGuy]

Thermostats are fairly inexpensive and it’s probably a good start. I would replace the thermostat, bleed the system, reset the codes, and recheck for the condition.

[John B Kobberstad]

Got the new good thermostat for it in the basement just need the gasket for it now. I was hoping to reuse the old gasket but there was no thermostat or gasket when I removed the thermostat housing. Wonder what else I’ll find after I replace it? I think I should have looked a lot closer before I made my offer to the guy when I bought it a couple weeks ago. Oh well! C’est la vie!

[mckrishes]

Hopefully this will be a simple fix. By the way, what did you end up doing with your other neon?

[John B Kobberstad]

The 96 Neon with the #4 P0304 misfire is back as the daily driver (150 mi/day) (until I get this 98 Neon fixed) for the wife and she’s not a happy camper. And neither am I!!

[EricTheCarGuy]

That’s good news. Keep us posted on what happens with the thermostat.

[John B Kobberstad]

Put the new 195 F thermostat in today. Now the fans kick on at about 212 F and turn off at about 202 F and the heat feels like it will burn my hand if I hold it at the center vent with the low setting on the blower at idle. It didn’t change how the O2 sensors were working though. Took the downstream sensor out and it was covered with soot so i cleaned it off with the wire brush on my grinder and did the propane test and determined that it was a bad sensor. Going to save it and put a new one in tomorrow. Will use the bad sensor to do a lacquer thinner catalytic converter cleaning (take the new one out and use the bad one while doing the cleaning then put the new one back in and save the old one to make a back pressure tester to use for testing catalytic converters as shown here.

http://www.youtube.com/watch?v=YPQBFvPTV14

[John B Kobberstad]

Changed my icon to a happy face. Found the info I needed which answered my query about the thermostat and the O2 sensors for my situation. Thanks to everyone who replied to it.

[John B Kobberstad]

P1281 was fixed with a new thermostat and gasket there was no thermostat in the vehicle when I bought it. I think the previous owner reset all the codes before I got there with my MT2500 scanner to check the vehicle because within a couple days everything started surfacing with codes. Everything is almost done just waiting on a few parts that are ordered to arrive then install them. Thanks to everyone who had helpful comments.

John

[dreamer2355]

Thanks for the update and posting the fix!

[Daniel]

I would change the oil when you get a chance. If this guy did clear the codes he may have attempted to smooth out any engine symptoms by putting a super heavy weight oil in it too. One of my uncles owned a used car dealership and would do that (which is why I stopped working for him)

[mckrishes]

That’s interesting, but not surprising.

[Author]

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