Greetings!

On my '98 SE with 120K Service Engine Soon light came on and stays. Pulled code P0450 "EVAP Fule line Pressure Sensor Circuit".
Anybody has had this problem? An Advice would be very helpful...

From what I was able to found on the Net, the EVAP Canister might need to be replaced.
Does anybody have a write-up how to do it? The Hayes manual only says "replace canister".
Thanks,

Eugene

 

Its pretty easy to change the canister. Its in the back of the car driver side. Right under the rear left wheel well. If you slide under your car and see it...you'll see that it is being held by only 2 10mm bolts and 2 or 3 hoses. Get underneath and look at for a few...u'll see how easy it is...but i am not sure if you need the whole canister replaced or if there is some sensor that is causing this....better find out for sure before u change the whole canister. I dont think they are cheap.

 

Thanks kenju4u!

I was wondering if fuel lines' pressure must be relieved, as with fuel filter replacement?

Eugene

 

If you replace your Canister, you do not need to releive pressure from the fuel system..... There are no fuel lines connected to the canister... Like Kenju said, check the sensor that might be causing your problem.....

 

This code is typically caused by a loose fuel cap or failed one. Try replacing it. If something else was wrong, I would have expected another code say (0446). 0440 with 0446 is a failed evap vent valve. This valve lets fresh air into the charcoal canister. Replacing the valve may require replacing the canister because the bolts holding the valve to the canister may freeze(rust) in place. A good price for the parts would be ($35 valve, $55 for the canister) dealer price. Shop around because the prices vary significantly. I just did this job a few weeks ago. BTW, the vent valve fails open because of corrosion. Don't waist your time trying to fix the valve.

Added:
Had a slight brain freeze when first posting above message. 0450 is Evaporative Emission Control System Pressure Sensor. This pressure switch is used for diagnostics by the ECU to make sure the evap system is not leaking and functioning properly. Three things could cause this. In order of likely hood: 1) vent valve (as listed above), 2) the sensor has actually failed, 3) the wiring to the pressure sensor has failed, ie corrosion. BTW, the switch actually triggers with vacuum.

 

Thanks Sandman1098!

 

U R Welcome!!

 

Thanks DougAtoms!

Indeed, there was a second code, something about solenoid, not a evap valve - unfortunately I didn't write it down, recet the ECU and this second code never came back. I recet several times the codes, but P0450 would come back in about a minute after engine's start.

The scanner I used was AutoTap which displayed "EVAP Fule Line Pressure Sensore Circuit". I don't mind replacing the canister with the valve, but where is the "Pressure Sensor Circuit"? I couldn't find it in my Hayes manual :-(.

Fuel cap seem to be alright - I wonder what could be wrong with it and is there a method to test it?

Thanks for your help!

Eugene

 

Dump the Haynes manual, its not what you need to properly diagnose and repair your car. Spend the money for the factory manual. It will pay for itself in the first repair you perform yourself. The payback off a Haynes is hit or miss. It's your money. My 2 cents is also free.
Now your questions answered:
The fuel cap always looks OK unless your kids play hockey with it. A new one is cheap (<$6). I'm 95% sure your problem is with the canister vent control valve (the solenoid valve directly bolted to the front of the canister, can't miss it). Replace this first and clear the DTC's. You can check the valve easily by appling 12vDC to the valve (polarity doesn't matter). You should hear a thunk as the valve actuates. It you don't, it's stuck. Don't try to repair the valve because this will only be temporary, replace it. BTW, no fuel should ever be in the evap system, only fuel vapors (don't smoke).
Onto the sensor: The evap system includes the gas tank void above the fuel (where the fuel vapors will collect). In order for the ECU to perform the evap diagnostic procedure, the fuel cap must be able to hold tight for the pressure test as well as the vacuum test. The pressure sensor (not really a switch) output is ~0.5volts at -2.76 inHg (vacuum) and rises to ~4.6 volts at +1.18 inHg (Pressure). As measured between the middle pin (terminal 2) and a good electrical ground. The connector needs to be connected to the sensor and the ignition key on. Use a small hand actuated pump (with gage) to generate the pressure/vacuum. The sensor is located about 6" fwd of the evap cannister and about 8" up from the bottom of the canister. Canister is located behind left rear tire. The sensor is bolted to the frame body of the car. Unbolt the bracket and disconnect the hose for the test, keep the electrical connector on the sensor. If all this seems too much, go see a qualified mechanic who uses the factory manual. BTW, the factory manual will also educate you on how all these systems work and make your car perform.

 

I replaced the EVAP canister vent control vavle a few weeks ago too. I was getting multiple EVAP solonoid codes even after reseting the ECU, but the most consistant code that came up was the EVAP canister vent control vavle. I replaced that and everything else was just fine.
About the bolts that hold the Vent control vavle. Make sure you take your time and spray some WD40 on it before turnging them. I had a hell of a time with one of the bolts. Its such a easy job but the bolt was stuck in the canister. I had to remove the entire canister and saw the head of the bolt off. Everything turned out fine but i dont think you will have that problem unless the bolts are over tightened on the canister.

 

I might have to sell my car because of all this EVAP BS...... My car has been giving me alot of problems with the EVAP system, and I might have to sell it..... I cant get it to pass the emissions test here in Georgia, and that means I cant register the car....... So, I may have to sell my car...... That Sucks!!!!!

 

Thank you DougAtoms and kenju4u!
Your advices were worth well over 2C...
Having sad that, I ordered Nissan Shop Manual from Courtesy Nissan ($135). They had four solenoids/valves listed in EVAP system and only two had in stock... So I ordered the Canister with the valve - the price sandman mentioned were about right - the canister was $39, the rest I don't remember but can post if anyone interested when I'll receive the parts, hopefully next week.(Courtesy is very good with shipments/tracking).

Anyway, I'll post the follow-up and thank you fellow maximatics again!
Eugene