P0401 more frequent at slow speeds

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Apr 22, 2007
Carpinteria, CA
I know there's a TON of P0401 threads and I've read most of them. I plan on doing all the things that are maint items that will hopefully get rid of it. Funds are tight right now so I'm looking for a place to start. I have new O2 sensors and will be putting those in as soon as I can get the bolts out of the exhaust.

So...I went on a few day wheeling trip and the 0401 kept popping up at slow speeds. Probably every couple hours. I get it occasionally under normal driving conditions (probably once a week) but I'm wondering if there is something that you guys know of that would be causing it to trip more often at slow speed? Also I cleaned the throttle body a month ago after I got the first code and then it seemed to pop up more often after the cleaning. Thoughts?
Clean the egr temp sensor and the passage in the intake through the temp sensor opening. Then get the cheap erg modulator and vacuum lines replaced.


Most likely the erg return or modulator is close to clogged.
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Sounds good. Thanks Q
I had the same problem on my 95 L/C. Once a week through a code and It would happen more with a strong tail wind. I thought It was O2 sensor but more likely It was a small exhaust leak at the bung. Install a new y-pipe and cats and put the old O2 sensor back In and no problem since Aug. My son thought It was the cats though, that ares is the only place under the truck that has bad rust. Good Luck.
This is an interesting topic, because I get the P0401, but only when I've driven at around 53ish mphs for 15mins or so. If I drive around town and keep it below 50mph it doesn't throw the code. I've used the fsm and replaced the modulator, all valcume lines, the vsv is new and within spec, and egr valve is working. I've also cleaned the 'intake port,' Yet I still get a code :(. last things is the temp sensor, which i've pulled a temp sensor from a 97 Carola as I noticed they have the same specs in the fsm to the lx's temp sensor, I just need to stick it on later this week.

All that being said, maybe p0401 doesn't ping at low speed is everything appears to work except the temp sensor.
I'm sorry I read to quickly My code was the p420 not PO401, good luck.
I seem to throw that code more often in warm temps Anything below freezing it does not seem to throw a code. Not sure what this means but that is what I have noticed.
Just follow the FSM tests to lead you to what may need replaced. That is the best way to save $$

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