# 2001 Altima and P0402



## brownsfan3785 (Mar 23, 2015)

I've got a 2001 Altima, 231k miles, runs great but the P0402 is pissing me off. I had the PCV valve changed for the first time and had a diagnosis completed for the P0402.

I had a tech tell me my EGR ports could be partially blocked which results in the exessive flow to the others.

Car runs great out of the garage when motor is cold.
After it warms up, i get a slight hesitation when i accelerate slowly from a stop.
1100 RPM @ 15-20 MPH and i can feel a small shake thru the gas pedal. Give it more gas and it goes away.

Does this sound like P0402? 
Sometimes I get P0303 along with it. CEL comes and goes. Gas mileage was crappy all winter long too.

Is it possible to clean this out without pulling the intake manifold off?

I replaced the BPT valve back in the fall.
I checked the EGR solenoid. works the way it should with battery voltage applied / removed.
All vacuum hoses (that i can see from above) look good. I've replaced a few over the past year or two.
Trying to knock out the simple stuff first.
FSM mentions camshaft position sensor and MAF sensor. Is there any other way to check these components other than thru the ECM? I'm not crazy about back-probing into the car's brain and having something go wrong.

Any help would be appreciated.

Thanks


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## brownsfan3785 (Mar 23, 2015)

Question about the hose that goes from the bottom of the BPT valve to the small pipe.

Inspected the hose today at lunch time. Hose is good.
I removed the BPT valve from the car.
I applied vacuum to one of the top connections and plugged the other. Bottom port remained open. Vacuum does not hold. If I understand the FSM correctly, this is the correct way to test this component and it is working as it should.

Now the real question:

Does the small metal tube that the bottom hose from the BPT valve connects to supply vacuum or exhaust pressure to the BPT valve?? is there an orifice built into this tube?? I'm wondering if I am missing a part.

I hope someone can help.


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## brownsfan3785 (Mar 23, 2015)

*weekend update*

Saturday morning i cleaned out the exhaust tube with the orifice the connects to the bottom of the BPT valve. That thing was gunked up real good. Got some bottle brushes and tried to clean out the EGR pipe at the EGR valve connection and EGR temp sensor location as best as i could. Used some seafoam and throttle body cleaner. Now I'm thinking maybe the problem was blockage on the exhaust side. No exhaust pressure to the bottom port of the BPT valve would trip the light. Correct? Anyhow, put everything back together, drove to auto parts store and got the light turned off. Still off as of this morning. Still have that little hesitation stutter going on every now and then.

Any thoughts?


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## brownsfan3785 (Mar 23, 2015)

*Monday update*

Monday afternoon check engine light returned.
Autozone verified P0402 again by itself.
Checked BPT valve operation on car.
At idle, applied vacuum to top port while plugging the other, vacuum does not hold.
Had a buddy hold the motor to 2200 RPM, applied vacuum to top port while plugging the other, vacuum holds. BPT valve functions as it should. 
I'm guessing the EGR pipe from the exhaust manifold is flowing the way it should as well. Producing enough exhaust pressure at 2200 RPM to activate the BPT.

Nissan FSM mentions testing the camshaft position sensor for the error code.
I'm wondering if this is the issue because of the hesitation the motor gets at low RPM.

BTW, i feel like i'm having a conversation with myself due to the lack of interest in this topic. Just sayin'..... 
..


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## rhsquicksilver (Mar 9, 2015)

Wish I could help, but it sounds like your working mechanical knowledge is much greater than mine, and have already tested what I would have suggested. Have you looked at replacing the O2 sensor and/or cat?
Even though I have a Honda, I did experience the same kind of hesitation you're describing, only I didn't know what to look for at the time, and later found a hose was just barely hanging onto a rubber sleeve on my intake. After that, good as new.
Currently throwing 0420 in my car too, but I know the downstream sensor is WAY overdue.

And yeah, I've tried posing questions/comments here too... Very slow and inactive, aside from the time that someone passive-aggressively called me out for being a spammer.


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## brownsfan3785 (Mar 23, 2015)

I appreciate the compliment about the mechanical knowledge. Turns out, I'm just following the Factory Service Manual step-by-step for code P0402. I'm thinking if it was the cat or o2 sensor, i'd be getting a different code.
Can't help but think it is the camshaft position sensor, mainly because of the hesitation coming off idle, like the timing is shaky but only at low RPM.

Cleaning the EGR ports is a task I'm not willing to perform just yet.
Only If i can do it without pulling the manifold. Any thoughts on internal cleaning agents. Can i dump a can of seafoam down there?


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## rhsquicksilver (Mar 9, 2015)

I guess that's where Nissan and Honda differ, as 0420 for me is a direct cat/downstream O2 sensor malfunction. Don't know much about the cam position sensor, but my guess is if it's reading wrong, your motor will let you know while there's no excessive force (I.e., throttle) masking the symptoms.
For SeaFoam, I've read a LOT of mixed reviews, but in terms of people using it wrong and then complaining about their car corroding before their eyes. I think so long as the pathway that agent will take won't scrub the lube off of any moving parts, that you'll have to then re-lube, or disintegrate an already half-gone seal or something (which it shouldn't) it should be fine. It definitely does its job when applied correctly. The motor oil will still protect the internals while running since it's actively pumping at the same time SeaFoam flushes through. Worth a shot!

Here's a link I used to read a little while doing a quick search if you want to read more about it. Granted, it's the company itself so take it with a grain of salt: http://seafoamsales.com/sea-foam-problems/


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## brownsfan3785 (Mar 23, 2015)

*Wednesday afternoon update*

I just noticed today, (Wednesday), that the tachometer seems to be behaving strangely. I acts like the "seconds" hand on a watch when accelerating with the O/D off. "ticks" its way up to 3,000 RPM. Put the car in neutral and rev it and the needle moves smooth and quick. I expect that in neutral. Does the camshaft position sensor trigger the tachometer on the dash?


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## rhsquicksilver (Mar 9, 2015)

Now that is odd, and unfortunately where my knowledge ends! I could only speculate from here that you're right. I think smj999smj needs to weigh in here, he's an ex-Nissan master tech. If he doesn't see this thread pop up, send him a PM to check out what you've expressed here.


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