ECU code P0440: Fuel Management System

[03_ga_se]

My check engine light came on, so I took it to Autozone and the code that came up was Fuel Management System. They said check the gas cap, did that and looks ok. Then check the EVAP and all connections for cracks. I'll do that tonight. Then it says to replace the purge valve.

Does anyone have any other ideas about what it could be or things I can check without spending too much money?

[rixGAphx]

Here is the complete list of related codes, from http://www.obdii.com/codes.html:
P0440 Evaporative Emission Control System Malfunction
P0441 Evaporative Emission Control System Incorrect Purge Flow
P0442 Evaporative Emission Control System Leak Detected (small leak)
P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction
P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0446 Evaporative Emission Control System Vent Control Circuit Malfunction
P0447 Evaporative Emission Control System Vent Control Circuit Open
P0448 Evaporative Emission Control System Vent Control Circuit Shorted
P0449 Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction
P0450 Evaporative Emission Control System Pressure Sensor Malfunction
P0451 Evaporative Emission Control System Pressure Sensor Range/Performance
P0452 Evaporative Emission Control System Pressure Sensor Low Input
P0453 Evaporative Emission Control System Pressure Sensor High Input
P0454 Evaporative Emission Control System Pressure Sensor Intermittent
P0455 Evaporative Emission Control System Leak Detected (gross leak)

Those are all relative to scavenging the vapors AFTER fuel injection/combustion/turning engine 'off'.
They are (almost) completely different from "Fuel Management System".

By all means, check those tubes and hoses.
Both visually, and using spray-starter fludi when the engine is running (if any gets sucked into the engine trhu a vacuum leak, the engine rpm increases).

'Check the gas cap' means
1) Make sure it's on square and tight.
2) Make sure the washer is sealing perfectly; this is easy for a shop to do if the have a fuel cap test rig. For us amatuers, it's easiest/cheapest to just buy a new cap, ~$10, once every 50k miles or so.

Do NOT buy a new purge valve!
That's what Checker/AutoZone want you to do: Just throw money at the codes, rather than analyzing what they really mean.
See codes P0443, 444, 445? If you get one of those codes, look more closely at the purge valve (if it's only about $10, I would be tempted to replace it as part of the analysis).

But for the time being, replace that 4-yr old gas cap and look over the entire SYSTEM.

Hope this helps,
-Rick

PS:
Your vehicles emissions system, including the vapor control system, is still under the federal (EPA) mandated 10-yr/100k warranty.
This is completely different from the original 24 mo/24 miles OEM bumper-tobumper warranty, and different from all extended service agreements.
GM is responsible if the car won't pass emissions, for just about everything except damage and neglect.

But they will charge you a non-refundable $80 diagnostic fee every time you roll in, and they'll blame you for damaging the gas cap washer.

Just keep this federally-mandated warranty in mind, and don't spend any big $$$ for a malfunctiong part.
Make GM pay if it's something major.

[daman]

The purpose of the Evaporative Emission system is to limit the amount of Hyrdocarbons released into the atsmosphere.
Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.
So in a nut shell if the control module senses a leak in the system that will allow more than a prescribed amount of fuel vapors escape, the module will illuminate the yellow engine light also know as the Check Engine (CEL)or Service Engine Soon (SES) light.
Depending on the year, make and model of your vehicle, this leak could be as small as .020” or twenty thousands of an inch ( a hole equal the point of a sharpened pencil lead)

Now with any diagnosis, the first thing we what to do after verifying the concern is to check the codes. This can be done at just about any chain auto parts store or if you own a code scanner, you can do it yourself.
DO NOT CLEAR THE CODE!!!!!!!!!!!!!!!!!!!! This is your key to finding out what is going on……we will clear the code after we repair the vehicle.

EVAP codes are considered either TYPE A or TYPE B codes..which in simple terms means the control module must see 1 failure for a TYPE A or 2 or more back to back failures for a TYPE B before the SES or CEL light is turned on.
Lets take a look at the codes and what they mean
P0440 or a P0455 – This is a Large leak indication or as people call it “The GAS CAP code”
This is a TYPE B code. Usually the code is caused by the gas cap being left off or loose after a refuel. This code could also be caused by any failure of the EVAP system that will cause a large leak.

for example P0442 – This is a Small leak indication.
This is a TYPE A code. This indicates a leak as small as .020”.
This code needs some serious diagnosis and knowledge of the system to find and repair the leak. Usually specialized equipment will be used to identify the leak.

and a P0446 – This indicates there is a restriction or blockage of the Vent Solenoid.
This is a TYPE B code. Any thing that prevents the venting of the EVAP system will set this code…usually dust and debris in the Vent solenoid or a damaged vent hose will cause this.

The other EVAP codes (P0443,449 etc) are electrical codes related to various components of the EVAP system.
Electrical codes need some good diagnostic skills, knowledge of the system and some specialized equipment.

With any car repair concern, there is a logical flow to follow when trying to identify what is going on..here in the GM world, we call it Strategy Based Diagnostics or 7 simple steps to diagnose a concern.
As always, verifying the concern and then doing a thorough visual inspection is key. It’s amazing how quickly a problem can be fixed by just the results of a visual inspection.
Now getting back to EVAP concerns….once you have identified the problem, you must come up with a repair, then a verification that the vehicle is repaired properly.
With EVAP leaks, usually a large leak is caused by a loose gas cap. Reinstalling the cap and clearing the code will be a quick remedy. But remember that you must always verify your repair..this could include professional intervention…(EEK!!!!!!!!!PAYING SOMEONE TO WORK ON MY CAR…..NO WAY!) . Well yes, this may be necessary..I have seen many times where people have come in to have a EVAP code cleared and refuse diagnosis only to have the light come back on…then blame me for the light coming back on…(then post on AF how the “stealership” did not fix their car).
But this isn’t a rant, this is information on what is going on.
Repair verification could include EVAP system testing with specialized equipment to verify that there are no leaks present..I personally check every EVAP system for leaks even if I find the customer left the gas cap loose…this insures that there are no other problems with the system that would cause the customer a trip back to see me. Far too many times have I seen someone tighten a gas cap and clear a code only to have the vehicle come back a few days later with a “real” EVAP leak…masked by a loose gas cap.
If you have a SES or CEL light caused by an EVAP concern and you have the code cleared and it comes back on after a few days….get to your local repair shop ( I recommend your local dealer with factory trained technicians) and have the system tested and repaired properly.
If you want to DIY the repairs, feel free, there are plenty of resources on the internet, but just don’t jump in and replace parts…educate yourself on the system and perform some diagnosis…many times a part will not fix the problem…$.02

[Jchiasson]

I did some research on this last week for my ride.... can't seem to find the link to the thread on it that I found most informative right now. But just putting on the new gas cap will not immediatly clear the light. The vehicle needs to go through 2 "drive cycles" before it will clear, if it's your gas cap seal.

[03_ga_se]

Thanks everyone for the information. The light turned off today after driving for about 10 miles. I think it was the gas cap. The car was last filled up by someone else, so I would assume that was the cause.

rixGAphx - thanks for the clarification. I must of heard the tech correctly or got confused when he told me what it was.

If the light comes back on, then I'll take it to a dealership.

[daman]

Glad to hear it..

[psychobooe]

I've been getting the same P0440 code for a while now also. It comes and goes randomly and it really is starting to bother me. I'm going to replace the gas cap and see where that gets me first.
Hey daman, how much would an EVAP system diagnosis cost at a dealership?
Thanks for the help.

[daman]

Originally posted by psychobooe

Hey daman, how much would an EVAP system diagnosis cost at a dealership?
Thanks for the help. [/B]

Not shure,, they probably would charge ya by the hour..

[HeyDace]

Depends on the hourly rate. We get $75 an hour. Which for diagnostics is pretty cheap. Most dealers in my area get $85-$95 an hour.

Problem is, that most people think for $75 dollars we will spend all day on it. If it will run over an hours time, we call and let them know it will take longer and they are responsible to pay the extra time. Its their call.