Need to pass inspection - reset light after repairs or let the car figure it out?

[brages]

This evening, I am doing some work on a car for a friend. Car (2015 Fusion 2.0) has a P0456 code (slight EVAP leak) causing it to fail emissions inspection. The owner would like to get the car inspected this weekend and update the registration before taking it back to college.

I'm replacing the purge valve because the forums say that's the common cause of this code.

Assuming this fixes it (!!!) -- is it smarter to clear the code or not? I am thinking if I clear the code, then ALL of the emissions monitors (i.e. catalyst efficiency) will need to reset before the car can pass. But if I don't clear it, it will probably take a few drive cycles anyway before the car figures out that everything's good. What's the smartest approach?

FWIW, I have Forscan (free version) - so maybe there's some way to reset just the P0456 without doing a full emissions module reset. Or maybe I'm just thinking about the whole thing wrong..?

 

[brages]

Also -- this is a capless system and I will be cleaning out the fuel filler as best I can...

I guess this is the "forum-guided parts shotgun" approach to repairs... it can be an efficient way to fix cars IMO.

 

[BHopkins]

I almost always clear the codes after making a repair. By clearing a code, I get to find out if my repair was correct, as the code will soon return if there is still a problem. If I don't clear the code, as you point out, it can take a while before I find out if the code clears on it's own, or not.

 

[rijndael]

I'm replacing the purge valve because the forums say that's the common cause of this code.

I would not replace parts as part of a guessing game.

You are likely to introduce a another problem ... new does not mean it works properly, especially if you buy aftermarket stuff.

 

[crashz]

Same, I usually clear the codes and look for anything that returns.

I've done the same. I usually research common issues, costs, then use a little diagnosis and a little brain power to determine if the forum solution is applicable. Then I aim and fire the parts cannon. Its both a learning tool and repair tool. We all can't be experts, but generally my methods have still proven cost effective. But my parts cannon has laser sights now

 

[brages]

the code will soon return if there is still a problem.

Yeah, that's my question: will clearing the codes mean that the car runs the EVAP diagnostic routine sooner or will it just run whenever the conditions (whatever they are) are met regardless?

 

[rijndael]

EVAP tests sometimes only run when the fuel level is between a certain range, like < 75%.

 

[racer12306]

The readiness monitors will need to be in the clear which takes starting and driving.

I had a situation several years ago where I had an EVAP code and wasn't in the place to fix it, and I was due for emissions check. I cleared the code, drove to work (55miles each way), filled up, drove home, filled up, etc etc etc for a couple weeks (probably overkill) to ensure that the monitors were ready and to prevent the EVAP test as @rijndael mentions and then I took it in and it passed.

 

[opus1]

The readiness monitors will need to be in the clear which takes starting and driving.

I had a situation several years ago where I had an EVAP code and wasn't in the place to fix it, and I was due for emissions check. I cleared the code, drove to work (55miles each way), filled up, drove home, filled up, etc etc etc for a couple weeks (probably overkill) to ensure that the monitors were ready and to prevent the EVAP test as @rijndael mentions and then I took it in and it passed.

^This.

I had to change the battery in the Cobalt 2 years ago, no codes or repairs, just yank the old and put in the new. I thought I'd driven it enough to reset things, but my first test failed because the test flagged 2 systems as "not ready". Tech at the test site asked if the battery was disconnected and when he found it was, he suggested I drive around some more and come back. I put 50 miles on the car, went back, and *still* had one system flagged as not ready, but the test allowed for that so I passed.

No matter how clever we think we are, the computers will almost always catch us.

 

[brages]

Here is something fun: "EVAP" isn't an acronym and should just be "evap". Same with your key FOB unless you are shipping it lol.

 

[michaelluscher]

Clearing the codes may force the monitor to run faster
In my experience, Ford's set the evap monitor best with between 1/2 and 3/4 full tank
If you can set out on a cold start drive with about that fuel level, you'll be in a better position
Try to work in an 8 hour cold soak post repair and code clear, and start the drive cycle from there

Here's a pretty good write up of a Ford drive cycle procedure
https://www.totalcardiagnostics.com...cle/View/41/7/ford-motor-obd-ii-driving-cycle

 

[thastinger]

Should take 2 complete drive cycles to clear. I'm not familiar with what the drive cycle should look like for his vehicle but they aren't usually just short road trips, there are usually some timelines to drive certain speeds and some slowdown criteria.

 

[SC Maintenance]

Does the manual give any hints as to how that actual system is monitored by the OBD?

The problem with clearing all the codes is then you have to wait for ALL the readiness monitors to reset. If that code resets on its own then only the evap monitor would need to reset - which may be faster than some of the others?

However sometimes it can take forever for the code to reset, and you don't know if what you just fixed did anything. Hence my first question.

You don't need to drive around randomly hoping the readiness monitors are set - a decent code reader - or even a cheap one these days, will tell you how many and which are set, so you can just monitor it and when there set head over for the test.

 

[dadto2]

I replaced a purge valve about 18 months ago, did not reset the CEL. After I finished my work, I started the car and the CEL cleared itself in like 300 feet of driving. I would just leave it and and drive. If you solved the problem, the CEL will turn off on it's own pretty quickly.

 

[AZjeff]

From the original post:

The owner would like to get the car inspected this weekend and update the registration before taking it back to college.

 

[John105]

The readiness monitors will need to be in the clear which takes starting and driving.

I had a situation several years ago where I had an EVAP code and wasn't in the place to fix it, and I was due for emissions check. I cleared the code, drove to work (55miles each way), filled up, drove home, filled up, etc etc etc for a couple weeks (probably overkill) to ensure that the monitors were ready and to prevent the EVAP test as @rijndael mentions and then I took it in and it passed.

My wife's used to have a P0420. Clear it, light goes off, but the car had to clear the shadow/pending. Disconnecting battery does not erase it. And yes, now 7/7 I/M categories are all not ready. After about 70 miles, 6/7 are. But the last one, EVAP, took 800-1200 miles.

Finally I proved it that 1 category can be not ready.

I've never looked at it this way--fix the fault, and drive, car will remove it. Will it? I think so?

I've done it the reverse. Once convinced parts needed, fix the fault, clear the code, drive to a ready state.

Again, will the car see after x cycles that the fault is gone, and turn off the check engine? I think yes, but have never done that.

 

[iCurious]

EVAP purge valve is one of the most common failure for small leak.

You can easily test it before you replace it. Blow air through the purge valve and it should not pass any air through. If it does, then it's defective.

 

[brages]

I actually watched a good South Main Auto video where he did some checks on the evap system (on a Ford Taurus). I am thinking I could run the same checks in Forscan.

Basically, he closed the purge valve and the vent valve and noticed that the tank pressure was going into vacuum, indicating a purge valve leak.

Then he put a vacuum gauge on the purge valve and showed that even when the purge valve was disconnected, the engine was still drawing vacuum through it.

 

[eljefino]

https://gatewayvip.mo.gov/readiness-monitors/

You're allowed two incomplete monitors, so, absolutely clear the code. Evap is the last monitor to run and if you're on the fence if you really fixed it, clear it, fill the gas tank, drive it around 40 miles, fill the tank AGAIN and take it in for the test. Having the tank near full precludes the test from running.

 

[ArrestMeRedZ]

https://gatewayvip.mo.gov/readiness-monitors/

You're allowed two incomplete monitors, so, absolutely clear the code. Evap is the last monitor to run and if you're on the fence if you really fixed it, clear it, fill the gas tank, drive it around 40 miles, fill the tank AGAIN and take it in for the test. Having the tank near full precludes the test from running.

Not all states allow two incomplete monitors. Evap will fail the smog test if it is in a fail condition and trips the CEL. Because the test requires so many conditions (see above) the smog test will pass if it is either in a pass or incomplete test state.
If you don't have the time to do the repair, or if you are unsure if the repair actually fixes the problem and you need to pass inspection, just do the above (fill tank, clear DTCs, do a couple of drive cycles, verify other monitors reset) and get it tested.