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I have been monitoring my 2002 Frontier 2.4L SES light for 3 months now. It seems to come on evrey 150 miles or so, but after about 200 miles and several starts it turns off by itself. The engine runs great and I have achieved 27-28 mpg consistently.
Just to see if there are any codes in the computer, I had it scanned at Auto Zone and the code P0402 is still in the computer, even with the SES light off.

I had it scanned 2 months ago and that same code came up. It means EGR flow is excessive. I inspected visually the EGR components and saw 3 small vacuum hoses to EGR valve, Transducer, and solenoid were cracked and deteriorated; I replaced them, but apparently the code is still in and the SES comes on and goes off. Is there anything possibly wrong with the software in the computer?

This is the second Nissan that I have problems with the SES. The 1997 Sentra I used to have (before my daughter totalled it) had a code saying the rear O2 sensor was bad. I changed it, reset the light, but still kept coming on every 200 miles. I then changed the front O2 sensor, and the same thing happened.
I thought the catalytic converter must have been bad, then, and changed that too, but still no joy. In the end, I just pulled the CEL bulb out, since the engine, ran always great otherwise.
Is there something congenitally wrong with these Nissan engine computers that throw codes with no real problems?
Just wandering......:thatswck:

Val Barone
 

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I would download the factory service manual for your truck. You can find it stickied to the top of our DIY forum. It's very good on how to check everything, even without Nissan's disgnostic computer - Consult.

Heath
 

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Got the same problem, but my sel stays on, Have a actron scanner so I can turn it off, try a few fixes, but lite comes back on. On OBD-Codes.com they claim the most common problem is the DPFE sensor is not working. I believe my EGR valve is OK and have checked for carbon blockage( it was damn dirty for sure). Taking it off isn't real easy, but doable. The DPFE sits on top of the EGR valve and some of the hoses didn't look to good, may replace also may be a lack of vacum. Truthfully there are lots of thangs to diagnose on this code, it's complicated. I also removed the hex head bolts and cleaned the ports, they were dirty, but not plugged. The factory service manual gives you PLENTY of thangs to look at. IF anyone has any advice on solving this code I'd appreciate.
 

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Discussion Starter #4
Thanks for all the ideas, guys. I have also bought a scanner and a Haynes manual and am experimenting with some fixes. My computer does not seem to like downloading the zipped online manual, however. It gives me a virus warning.
So far:
I have replaced all the little vacuum hoses, which were appearing hard and deteriorated.
I have sprayed carb cleaner in the vacuum ports and they appear to be clear. I have used a large syringe to pull vacuum from the EGR valve; it opens and maintains vacuum. Also, with the engine running, moving the EGR valve disc by hand stalls the engine, which tells me it is working.
I have removed and tested the vacuum solenoid, and cleaned the ports with carb cleaner. All is OK, there as well. II have not actually tested the Backpressure transducer yet, but I have found the procedure in the manual, and that is my next step, along with checking for actual voltage presence at the solenoid with the ignition in ON.
I am leaving the EGR removal and cleaning for last, since it is such a pain to do; I just can't see the space to use tools to remove the valve, unless several other parts are removed first.
As I wrote to Heath earlier, it seems that 71000 miles should be somewhat early for the EGR passages to carbon up that badly.
I am using the scanner to erase the code (always P0402) after each attempt at a fix, to see if I am successful, and will post any progress. I am lucky that there is no smog test to pass in my area (NW Florida)
Cheers,
Val Barone
 

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THanks for the info, I haven't looked at the vacum solenoid yey, but cleaned the egr valve. I sprayed the 2 bolts down with liqued wrench along w/the flare nut. You DAMN SURE DON'T WONA BREAK ONE. You can sneak a ratchet and socket from the back side, but had to remove heater hoses from firewall to get access along with all the bpt junk. The flare nut on the tube going to the egr was a pain, I finally said to heck with it a broke it lose with a large pair of channel locks. If I hadn't sprayed down with liquid wrench I probably would have broke somethan.
Another good web site for info & to download manuals from is nissanhelp.com. Also obd-codes.com has a lot of usefull info. Hope some of this helps, let me know if you crack the code & I'll do the same.
 

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THanks for the info, I haven't looked at the vacum solenoid yey, but cleaned the egr valve. I sprayed the 2 bolts down with liqued wrench along w/the flare nut. You DAMN SURE DON'T WONA BREAK ONE. You can sneak a ratchet and socket from the back side, but had to remove heater hoses from firewall to get access along with all the bpt junk. The flare nut on the tube going to the egr was a pain, I finally said to heck with it a broke it lose with a large pair of channel locks. If I hadn't sprayed down with liquid wrench I probably would have broke somethan.
Another good web site for info & to download manuals from is nissanhelp.com. Also obd-codes.com has a lot of usefull info. Hope some of this helps, let me know if you crack the code & I'll do the same.
I have done quite a bit of research on the web on EGR systems, including the obd-codes.com. Even though they all work the same way, on our vehicles they are the computer-controlled pulse type. The solenoid operating voltage from the battery is either applied or removed by the PCM computer several times a second so that the resulting pulse opens and closes the vacuum passages through it, and, consequently, through the BPT, which, in turn opens and closes the EGR valve itself. Therefore, it is good to check that the solenoid receives voltage to begin with. That is easy to check with a voltmeter applied to its connector and the key in ON.
What I also learned is that the SES light comes on when the fault has been detected at least twice, which is stored by the computer as a "pending" code.
Immediately after the SES came on, I shut off the engine and scanned the PCM: sure enough, the code was in there twice. After driving several trips with the light on, however, the light turns off by itself on startup, but another scan indicates the code is still in, but only once. This tells me that the problem is intermittent. Infact, it has acted that way for the last 4 months. I have been tracking the odometer readings each time the light comes on and goes off. After I am done checking that the vacuum is present at all components (EGR valve, BPT and solenoid) and voltage is present at the solenoid, logic steers me into thinking that some amount of carbon prevents the EGR valve poppet from seating fully when no EGR flow is required. That is why I want to clean it as a last step.
As far as I can tell, I have no driveability issues with the truck, but only a slightly elevated idle speed on cold startups. Then, everything is normal with a warm engine.
Until next time......:noworries:
 

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Good info. I have about the same symptons as you, elevated idle speed on cold start, course once my sel goes on it stay's on. As far as the egr valve was I figured as dirty as it was that cleaning it would solve my problem, no such luck. From reading your post I can tell you would probably have better luck than me at understanding the service manual, it's easy to download on nissanhelp.com. After registering just punch in p0402 in the search engine, you will get some vary intesting post's, one gives a link for a 2001 frontier, by using that limk it's quit simple to go to your year. untill next time...
 

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As far a checking the egr control solenoid spray a small amount of silicone lube in it and tap it with a srewdriver, then with the key on/engine off just work the wiring connection on and off tall hear the solenoid working the valve.
Don't forget the fuel filter as I'm sure changing that was what cleared my code for good. With my actron9180 the freeze frame data was showing the fuel was leaning out each time the code was set.
 

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Discussion Starter #9
As far a checking the egr control solenoid spray a small amount of silicone lube in it and tap it with a srewdriver, then with the key on/engine off just work the wiring connection on and off tall hear the solenoid working the valve.
Don't forget the fuel filter as I'm sure changing that was what cleared my code for good. With my actron9180 the freeze frame data was showing the fuel was leaning out each time the code was set.
What finally fixed it was cleaning the 4 EGR ports on the intake manifolds. They are accessible with an allen socket only after removing the throttle body itself.
The shop that replaced the throttle body following my problems with the Seafoam application took care of that, and the SES light has not come back in almost 2 months. I had a bad argument with that shop because they replaced only the top part of the throttle body along with the MAF sensor, while replacing the lower part, (the part with the butterfly) with a used part.
The idle speed is finally within limits, now (750+/-50 RPM).

Val in Florida
 

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Yep I cleaned the EGR ports but wuz still getting the code, my problem was most likely a pluged fuel filter that was causing problems, course I'm glad I cleaned the EGR valve and vacum lines.
 

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What size allen wrench do I need? It seems to be between an 8mm and 9mm wrench. Is it an 8.5mm or SAE?
 

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First, I am not a car mechanic by trade, but make a fairly good living pulling wrenches.
Could not remember which allen wrench I used so went and looked at my metric and SAE allen wrenchens in my garage and it is a guarentee I pulled mine with a 5/16 allen wrench, yep it's the only one marked up. You better have a vary good set, as a cheap set WILL NOT remove these and it ain't a job for the faint of heart. Got real ugly getting these out, hope this helps
 
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