EGR P0402 chat GPT

[mosilvia]

Hi, P0402 came on so I clean up the O2 sensor, MAF sensor, EGR valve, check EGR bpt valve.
All parts are good.But still came on.
So I asked Chat GPT.He said replace EGR temperature sensor.
Is that true?

[VStar650CL]

Possible, but that code is usually from carbon fouling in the intake manifold, fooling the temperature sensor and making the ECM think the EGR is stuck open. The code is nominally caused by too much EGR flow, but the ECM derives that from the temp sensor.

[mosilvia]

So the most important thing to do is to clean the exhaust manifold?
If so,Is it possible to clean it up without removing the exhaust manifold ?

[mosilvia]

Sorry, intake manifold

[VStar650CL]

One of the guys at our shop still has an old speedo cable he used for that, you stick it in a drill and snake it in to knock the carbon off the intake runners. Short of pulling the whole plenum, that's the only quick fix I know about.

[mosilvia]

What about carbon after cleaning?
Vacuum?

[VStar650CL]

Once it's broken loose it will pass through the cylinders and burn up in the cat. You don't get any "chunks" like you get when decarboning valves, so there's little risk of damaging a spark plug either.

[mosilvia]

Nice!! Thank you for the great idea.
I clean 29years of carbon.

[VStar650CL]

[mosilvia]

I cleaned the interior of the intake manifold last November. I removed the Idle Air Control (IAC) valve and the throttle body, then cleaned them using parts cleaner, a brush, and a towel. The check engine light went off after that, but recently—once again—the P0402 code has started appearing. I consulted with Claude, and he suggested that the EGR solenoid valve is the likely culprits; I intend to replace them, but I would like to confirm: is the correct part number 14956-41U00? Also, since this part is located between the engine and the firewall, is it possible to remove it without having to pull the engine?

[mosilvia]

I cleaned the EGR valve and IACV too.

[mosilvia]

https://imgur.com/a/nX3gWrl
https://imgur.com/a/dvEPfk0
https://imgur.com/a/j314E7G

[mosilvia]

Also, could you double-check that the tubing for the EGR BPT valve is connected correctly? The tube on the right side of the BPT valve connects to the EGR solenoid valve. (Note that this differs from the service manual, as I have installed an aftermarket fuel pressure regulator.) Furthermore, is the EGR solenoid valve typically located somewhere to the left of the IACV? In the second final photo, it appears to be situated directly beneath the cylinder head; however, on my KA24DE engine, it is not located there.https://imgur.com/a/ajn0udj
https://imgur.com/a/vdRvQ3V

[VStar650CL]

P0402 basically means the ECM thinks there's too much EGR flow. Carbon restricting the intake port (what I suggested you clean previously) holds heat causing the EGR temp sensor voltage to read artificially hot (low) after the EGR shuts off. That makes the ECM think the valve is still open even though the solenoid is off and the valve is closed. If intake carbon isn't it, then the next most likely cause is that your EGR actually is stuck open. I seriously doubt it's a problem with your hose routing because the code didn't come back for 8 months.

[mosilvia]

Thank you as always for your replies. I have confirmed that the EGR valve is operating within the 2,000 to 4,000 RPM range, exactly as described in the service manual. It is possible that my cleaning of the intake manifold was insufficient; however, I only cleaned the section between the throttle body and the IACV, rather than the entire intake manifold assembly. By the way, is the EGR temperature sensor located within this specific area that I cleaned? I looked inside, but I couldn't find anything that resembled it.

[VStar650CL]

IIRC (it's been a long time) it's in the lower manifold right between 2~3.

[mosilvia]

Thank you. I will clean the intake manifold once again. Incidentally, I inspected the EGR BPT valve, and it tested normal. Just as a hypothetical—if the P0402 code persists even after cleaning, what other causes might be possible?

[mosilvia]

I replaced new rubber hose connecting the gas tank to the filler cap because fuel was leaking whenever I filled the tank to capacity; however, the leak persists, and I suspect there may be a crack somewhere near the top of the tank. Could this issue be related to the P0402 diagnostic code? I suspect the tank is indeed cracked because—with very few exceptions—I rarely hear any pressure being released when I remove the fuel cap.

[VStar650CL]

If the BPT and EGR circuitry all passes muster and the EGR functions when it's supposed to, then the only things besides carbon/heat buildup which can cause it are an EGR valve leak (opening and closing normally but not sealing) or a bad EGR temp sensor. The temp sensor is the only dynamic feedback the ECM has, so what it looks for is high or low temperatures persisting when they shouldn't. It interprets high as a valve stuck open and low as a clog or stuck shut. The thermal conductivity of carbon is awful, it takes forever to shed heat which is why it makes the sensor read higher than it should long after it should have cooled down. That fools the ECM. For P0402, anything that makes the sensor read artificially higher temperature (lower voltage) than it should at idle will trip the code.

[VStar650CL]

I replaced new rubber hose connecting the gas tank to the filler cap because fuel was leaking whenever I filled the tank to capacity; however, the leak persists, and I suspect there may be a crack somewhere near the top of the tank. Could this issue be related to the P0402 diagnostic code? I suspect the tank is indeed cracked because—with very few exceptions—I rarely hear any pressure being released when I remove the fuel cap.

Very doubtful. The EGR has no direct link to the evap system, and while the arrangement of a manifold could conceivably dump purge on the temp sensor and artificially cool it, I can't imagine any circumstance where it would heat the sensor up. On an old ride like that, you may just have an evap canister that's seen better days and is leaking or is too flooded to function when you fill up.

[mosilvia]

How do I check for leaks in the EGR valve? Also, is it possible to replace the EGR temperature sensor without removing the intake manifold?

[VStar650CL]

How do I check for leaks in the EGR valve?

Compressed air. Turn the engine to about 90 deg past TDC so there's no valve overlap and pressurize the exhaust pipe. Then listen for air coming past the EGR into the plenum.

Also, is it possible to replace the EGR temperature sensor without removing the intake manifold?

IIRC the upper has to come off but not the lower.

[mosilvia]

Thank you I try if turn the light after cleaning

[mosilvia]

https://imgur.com/a/7YVsr6l

Do you think these parts would fit an S14? Or has anyone here already installed them? Judging by the photos, they appear to be absolutely identical to the stock S14 parts. Also, the listing states that the EGV450 is for manual transmissions while the EGV482 is for automatics; is there actually any difference between the manual and automatic versions?

[VStar650CL]

I'd imagine the M/T valve would have less damping and be faster responding than the A/T to account for sudden shift conditions, but I doubt there would be any difference in flow. So I'd say it's probably okay to use the M/T version on an A/T, but maybe not the other way.

[mosilvia]

Thank you Vstar650cl !!

[VStar650CL]

[mosilvia]

https://imgur.com/a/vyn3oXL

[mosilvia]

https://imgur.com/a/J9YrtW5

[mosilvia]

Hi, these are same parts?
I replaced brand new this parts every 2 years.
This part breaks every two years—is that normal?