OBD2 makes my head hurt

[tRustyK5]

We have an '02 Durango, which has had a check engine light on for ~2 years now...

No drivability issues, just an annoying light. It needs it's first emissions test this month so I broke down and picked up an Innova scanner to see what code was set. P0440 set, evap system. Most common issue I know of for that code is gas cap related, so I pick up a new gas cap, clear the codes and re-scan. shows no codes, but I have an amber light on my scan tool. This tells me the computer has not run a diagnostic on one system (evap...duh)

I break out my google fu and dredge up the parameters the PCM looks for before running the diagnostic. It's a two part deal, the first part runs after the truck has been idling for 5 minutes, then driven at 35-45 mph for 2 minutes. The fuel tank must be between 50% and 85% full. The second part occurs after the trcuk has sat for at least 8 hours without being driven (cold soak). Start from cold, idle for 4 minutes, then stop and go traffic for at least 5 minutes (smooth accel and decel) then let it idle for another 4 minutes...

What kind of idiot comes up with this? I make a repair, and basically have to make this my daily commuter for the next week and hope against odds that the computer will finally see the stars align and do the self diagnostic...all so I can confirm we had a bad gas cap. Until it does this self diagnostic I can't take it in as their scan tool will show the evap system diagnostic is in a "has not run" condition.

Happy with my scan tool though...it does all the generic OBD2 codes, as well as the manufacturer specific codes (broken down by engine, tranny, etc), also does live data, and of course tells me which systems have or have not run self diagnostics.

Still...this is way too much tech for a bad gas cap.

 

[samsterman99]

Does disconnecting the battery clear everything? And hopefully the computer will start fresh and won't require the tests?
Also is it easy to pull the bulb for the CEL, that is always an option if you have to go get it tested and the light is still on.

 

[MTChevy]

Evap codes suck. Most of the time its a cracking rubber hose. Getting the system smoked is the fastest way of diagnosing and fixing a leak in the system

 

[tRustyK5]

Does disconnecting the battery clear everything? And hopefully the computer will start fresh and won't require the tests?
Also is it easy to pull the bulb for the CEL, that is always an option if you have to go get it tested and the light is still on.

The scan tool has an 'erase' option that clears everything. That part isn't hard, the issue is the E-test facility uses a scanner that can also tell if the PCM has run all the systems self diagnostics...same as the scanner I'm using. It's not enough to not have a check engine light. Removing the bulb would have no affect as the scanner will still be able to see any codes, and the "has run/has not run" condition of the systems self diagnostics. It's a lot smarter and more comprehensive than the older OBD1 stuff was.

Currently there is no check engine light, I'm about 99% certain it was just a bad gas cap. I'll use it to get to work and back this week and check it again on Wednesday. It should have met conditions by then...

 

[tRustyK5]

Evap codes suck. Most of the time its a cracking rubber hose. Getting the system smoked is the fastest way of diagnosing and fixing a leak in the system

Was reading that a lot of rental fleets were throwing the P0440 code a few years back. All it took was a slightly loose gas cap, or a fill with the vehicle running. This particular code is almost specific to the gas cap. There are about a dozen generic codes the Evap system can throw based on what the self diagnostics find.

A 10 year old gas cap probably needs replacing anyways. I've had three gas caps fail at emissions testing on various vehicles I've had to get tested so I know it's a pretty common problem.

 

[4X4HIGH]

On OBD2 systems ALL of the monitors have to be set before you will be able to pass an emissions test. This usually requires about 50 miles of driving without any issues after any codes have been cleared.

 

[sweetk30]

mopar had a huge problem with cracked rubber conector hose under the hood on 1 of the evap / aka charchole canister vent lines.

p0440 is a generic evep leak code and do your self a favor DO NOT JUST THROW PARTS at these 96-newer rides. if you read and use the scanner right you can pin point the problems faster and cheeper.

and gm for years has had bad evap vent solinoids and even has a fixer update kit for them.

 

[imiceman44]

I dealt with this on my wife's 2003 honda and after going to the dealership and they tell me most likely the gas cap so I change it and a week later it come back on, so I left it for a year then when it came time for smog, I went to my smog guy and talked to him, he went in checked the code, yep you guessed it, then he clears it and says, go drive it for half an hour and come back if the light doesn't come back, we'll run it.
Well the light didn't come back so we smogged it, then after a month it came back, so I talked to him about a few things and he mentionned the overfilling, and I said I always top it off, so he said THAT will also trigger it.
We stopped topping it off and with a new cap, we got a full year with no problems.
Now I don;t know if the 30 min of driving was enough time for getting all the internal testing done, and if the guy was doing anything wrong by passing me or not but he did make me drive it the 30 min before he tested it.

 

[tRustyK5]

On OBD2 systems ALL of the monitors have to be set before you will be able to pass an emissions test. This usually requires about 50 miles of driving without any issues after any codes have been cleared.

My scanner shows which monitors are in a "have run" condition and which ones are in a "have not run" condition. Evap is the only one pending.

Brett, I wouldn't call replacing the gas cap throwing parts at it. It was $9. the light initially came on and went out a half dozen times before just staying on. A cracked line would have set a code and kept it. A gas cap with a seal going bad would behave exactly like the intermittent issue we started with.

We'll find out for sure soon enough, and I'll post up an update after the monitor for evap "has run".

 

[sweetk30]

not saying isnt a cap or your tossing parts. just info for you and others to use.

seen dozens of the mopars get fixed with the hose bad. its about 2-3" length .

and evap monitor is last to run and must be over 1/4 tank and no more than 3/4 tank on most models to run.

and yes bad to cram gas in 96-newer rides. once it clicks round to next buck and stop is safe. but dont keep cramming gas in tank .

 

[496truck]

To answer the question "Why do they go through all that?" It's to make sure the vehicle is fixed and not polluting. There once was a time when you could clear the codes right before the test, pull it in for the plug in test, no codes would pass and get a sticker, then pull it out. Light would come back on as the car pulled out of the lot cause it was never fixed.

Now you have to wait for the computer to be in readiness mode, basically meaning it has run all it's self tests and all is good. Every car brand is different. For some all it takes is a 30 minute drive time. Others want 50 miles with no time line. And some want different parameters for each system self test (lucky you).

 

[tRustyK5]

I understand the reasons behind the self tests etc, what annoys me is the parameters for some of the self tests the computer does are pretty 'out there'. If I just told my wife to drive it like she normally does it'd never self check the evap system...

 

[sweetk30]

fyi be glad its not a gm s10 with 4.3 v6 and stick shift. . . .

seen a few take over 500 miles to run and one took 1k miles.

some vehicles are so bad to run monitiors that in new york state thay are exempt from monitor check only codes get read.

 

[1BEATK5]

The fuel cap will not fix your problem. If you had a fuel cap leak, you would have had a P0442, P0455, or P0456. Those dtc's are for leaks after the pump.

What you have (P0440) is a general evap failure. Which means that the leak is before the pump. So, you need to do some investigating. Follow all the hoses from the throttlebody to the canister and pump.

if its a 4.7l. Find the hose on the drivers side, just behind the t-body. It goes from there, under the battery tray and over the the purge solenoid. The purge solenoid is behind the headlamp by the battery. Replace all cracked hoses. Then look under the truck on the drivers side in front of the fuel tank. There are 3 "u" shaped hoses that connect the canister to the hard lines and the pump. Replace all cracked hoses.

If you didn't find any cracked hoses, then you will need to replace the pump.

If it has a 5.9l the only difference is that the hose connects on the side of the intake. Not by the t-body.

 

[diesel4me]

Most of the time when my friend has a vehicle that shows an "EVAP" code on the scanner--it turns out to be a severely rusted filler neck going to the gas tank more often than not!....salt eats them rapidly here!...and new ones aren't cheap,up to 200+ bucks in a few vehicles he had to buy new ones for,when none could be found in junkyards that were any good...one car had such large rust holes in the filler neck,the tire slung about 2 gallons of water and mud into the gas tank!.....

 

[tRustyK5]

The fuel cap will not fix your problem. If you had a fuel cap leak, you would have had a P0442, P0455, or P0456. Those dtc's are for leaks after the pump.

What you have (P0440) is a general evap failure. Which means that the leak is before the pump. So, you need to do some investigating. Follow all the hoses from the throttlebody to the canister and pump.

if its a 4.7l. Find the hose on the drivers side, just behind the t-body. It goes from there, under the battery tray and over the the purge solenoid. The purge solenoid is behind the headlamp by the battery. Replace all cracked hoses. Then look under the truck on the drivers side in front of the fuel tank. There are 3 "u" shaped hoses that connect the canister to the hard lines and the pump. Replace all cracked hoses.

If you didn't find any cracked hoses, then you will need to replace the pump.

If it has a 5.9l the only difference is that the hose connects on the side of the intake. Not by the t-body.

So as predicted P0440 reset and the check engine light is back (at least the gas cap is good for sure now...lol). I've gone through and checked all the rubber lines, the three "U" shaped ones by the tank and everything under the hood. All the lines are pliable and normal feeling, no cracks that I can find, no rub spots etc etc.

Three questions: First is I see midstream on one line a green cap covering a schraeder valve. I can snap a pic or two if that helps. Is this part of the EVAP system and is that valve used for test purposes or?? Second, is there a way to test the purge pump? Third, how is the "smoke test" done and do you need special tools or??

I was willing to waste $9 on a gas cap, but beyond that I'm not a big fan of throwing parts at a problem and hoping for resolution.

 

[sweetk30]

green cap is test port for evap.

takes special size core tool to remove the core to testand IS LEFT HAND THREADS NOT RIGHT HAND if removed wrong will strip out the plastic threads.

and smoke machine setup of some kind is needed. and psi is under 1 pound of pressure to test basicly its so small you can hurt it if you blow in it wrong.

and mopar has test options if you have a fancy scanner .

and you need a good scanner for smoke test to turn vent valve on/off for testing.

 

[tRustyK5]

So...best to take it in somewhere then?

 

[sweetk30]

if your not setup to do it and dont wana pull what hair you have left out then best to man up and say screw it pay the garage.

i hate to say it my self but this is a tricky area there is not much way around on evap leaks.

 

[tRustyK5]

Thanks, doesn't sound like something I'm gonna mess with. I really hate paying a shop to do stuff, but I do know a decent place.