My wife's 03 Maxima just popped the service engine light. Came up with code p1491 EVAP vacuum cut valve/bypass circut malfunction. Does anyone have a good suggestion as to where to begin looking to diagnose/fix the problem. My first real dealing with the Nissan. Will take any help I can get. Thank you...

 

The FSM (Factory Service manual) tells you what might be wrong and what to check when your car throws P1491:
- Vacuum cut valve bypass valve
- Vacuum cut valve
- Bypass hoses for clogging
- EVAP control system pressure sensor and circuit
- EVAP canister vent control valve
- Hose between fuel tank and vacuum cut valve clogged
- Hose between vacuum cut valve and EVAP canister clogged
- EVAP canister
- EVAP purge port of fuel tank for clogging

I would start by checking the hoses. Re. the FSM, you can get it from here: http://boredmder.com/FSMs/Nissan/Maxima/

 

Thanks for the info. Can you tell me what part of that manual I would need to download??

 

Find 2003 folder... Download the IDX file... Search for EVAP... Download the EC file...

In the EC file search for your code p1491... Takes you to page EC-598.. Try out the testing without a CONSULT-II

Some of the parts are located underneath the car near the rear driver side area...

 

Check the purge valve attached to the EVAP canister behind rear driver side wheel- it is prone to get stuck in open position. If you're lucky and will be able to remove it you can spray it with some WD40 and cycle few times with battery voltage, it cured mine just fine (already put several months on it). To check the valve you can try to blow air through it with your mouth- you should not be able to when it is closed. You should also hear distinct clicks when it is engaged/disengaged 'manually' from external 12V power source.

Another option would be to spray / cycle with valve in place. This would spare you trouble of dealing with those M6 (10 mm head) bolts holding canister in place. Due to rust I broke 3 of them holding canister to its bracket and then other 3- holding bracket to the body. I had to drill out the remainings and re- cut the threads, not fun. 2 other bolts holding valve to the canister also broke, the canister's plastic around one of them was cracked too. I epoxied cracks, re- cut the threads and all is well since then .

New canister costs ridiculous money and it's nothing more than plastic box with charcoal inside, it doesn't go bad. It is one of few places in the car where I consider 'ghetto approach' to repair acceptable.

 

^Sometimes they do go bad by the charcoal getting loose and clogging up the lines making you have to replace the unit and blow out your evap lines with compressed air to get the charcoal out. Sad, but true.

 

Start by checking the hoses as Maxiiiboy said. They could be getting stiff and brittle, which makes them crack and leak.

Next step would be to remove the wire harness connector and check the coil of the valve resistance. I don't know what the resistance reading should be, but in general these things should be in the 20 to 50 ohm range. If the resistance reading is real high, then it is bad.

Then see if the valve is getting the voltage to operate. Follow the FSM for how to do this.

 

Thank you Dennis for the picture . Statistically speaking- EVAP Canister Vent Control valve on the picture is the prime suspect following by the cracks around the place it is attached to the canister. I had this problem twice on each of the Maximas I owned and nothing else ever went wrong in EVAP system in those cars. Valve usually remains stuck in open position due to rust/debris, its coil checks fine, wiring is fine but if you take it out you either don't hear the clicks when applied battery voltage or you can blow the air through with your mouth when it is supposed to be closed, hence creating the leak. The rubber hoses are usually good at this age of our cars.

I have never heard of the charcoal clogging the EVAP lines in Maximas and creating problems. I don't actually see why clogged EVAP line would be a problem or how this could even happen- there's not much flow there to suck something in. Usually EVAP system fails the vacuum test regularly performed by ECU and that place is famous for causing this.

 

Thank you very much for all the info. This should be a big help. You guys are great.

 

The FSM mentions pulling off the hose at the base and checking to see water doesn't drain out.

 

https://maxima.org/forums/4th-genera...-up-lines.html

https://maxima.org/forums/4th-genera...-charcoal.html

I'm not seeing any threads on this in the 5th gen section.
Must have been a defect in 4th after it gets real old or just no one has noticed it for the 5th yet.

 

One more question. Since its insanely cold at the moment. Is it going to cause any serious issues, if I don't get to it for a couple of days?

 

No, nothing will happen in months, let alone days. The only unpleasant side effect is SES light which you have to live with and inability to see if other unrelated problems happen to trigger the light later on since it will be already lit for this reason. Good OBD reader will pull all the codes though.

 

Good deal. Not planning on letting it go anywhere near that long. But, with wind chills well below zero. And, not enough room in garage. Its gonna be a day or two.

 

I lost gas pressure (the gas **** didn't make that noise) and lower fuel consumption until I fixed it :S

 

That is hardly possible- gas pressure is created by fuel pump, completely different device. If anything you should've gained the pressure as EVAP system maintains negative pressure above gasoline surface. Something else was amiss.

IMO EVAP system prevents gasoline vapors from escaping into atmosphere. It has to maintain negative pressure so in case of small leaks it would suck in air instead of releasing gasoline vapors. I'm not sure about fuel consumption as well- it's not part of fuel ratio loop but I might be missing some indirect effect here. In any event it would be much less noticeable compare to failed O2 sensor or to short daily commute pattern for example.

 

One of the hoses connected to valve opens to atmosphere. If you can reliably extend it or replace with longer one you could check its operation without removing it from the canister. I really do not envy you with those rusty M6 bolts and cold temperatures. Something happens to the metal of those bolts- their heads simply shear off under not so high torque when you try to unscrew them.

You might want to soak those bolts WD40/Liquid Wrench/PB Bluster meanwhile. Didn't work for me though after 2 days and around 70 degrees temp: the car smelled like Liquid Wrench itself, everything there was dripping it and I still couldn't unscrew even single one of them. If someone knows how to tame those suckers please share the experience as heating them is out of question due to proximity of gasoline vapors.

 

As annoying as a couple of things have been on this car. Using fire to remove bolts is starting to sound like fun. Its just had some issues (none super major). But, annoying. Good thing for it, that my wife loves it.

 

 

Folks,

I know this is a really old thread, but I have the issue. . .
I have a 2003 Maxima. I have been getting this code for a while now. It disappeared for a while, and lately it pops back up after maybe 20 miles after CEL clear.
I followed what this thread says, I have checked hoses and the valves as suggested. I see no issues. I did the activation tests and all. Did them using the diagnostic tool I have, and also by removing the valves and giving them direct 12V. All is well and works as expected.
Years ago I had a code which turned out to be the canister so mine is not the original with the car, but an OEM Nissan one still. I tried with another canister and the valve that came with it (used), but the issue did not resolve.
I am currently at a loss. Ideas?

 

OEM senors, and check the Evap Purge Volume Control Valve (in the engine bay)

sometimes the valves connected to the canister rust and cuase a leak and you can caulk them to get by. but don't forget theres one more sensor in the engine bay,

i did circles and it ended up being the on EPVC in the engine bay. heres a nother thread form 4th gen that relates to 5th gen EVAP set up

https://maxima.org/forums/4th-genera...-p446-bah.html

 

Thank you, I will check that out as well.

 

Well. . . I went through everything again almost two weeks ago after the last post. I gave it time to see what happened. The CEL did not come on with the P1491 until yesterday, but it still did.
I am at a loss here now. . . Unless I just start replacing parts and hoses idk what else to do. But all 3 of the valves checked out. The two by the canister, the one on the manifold under the hood. . .

What do I do? It is annoying more than anything since we have no emissions tests here, but I hate the CEL being on, and resetting it all the time means the ECU cannot function in normal mode. It is always in learning after a reset.

 

new oem sensors only, and if you still have the one code used advanced search around here for that code. it sounds like u didnt replace the valve by the canister, just with a used one.
if no luck take it to a mechanic to do a smoke test etc etc.

i dealt with that code it takes a while to narrow down and some parts. the most expensive you already did was the OEM canister, but if that wasn't NEW it can't be ruled out.