Evaporative Emission Diagnostic P0446

John Instructor Beaver, Pennsylvania Posted   Latest   Edited  
Case Study
Driveability
Emissions
2005 Chevrolet Cobalt 2.2L (F L61) 4-spd (4T45-E)
P0446 - EVAP System Vent Control Circuit
Cannister Vent Valve
Performance

Here is a video for an evaporative emissions system diagnostic for a cannister vent valve performance code. The key points being how to leverage scan tool functions while making physical changes to the vehicle in order to prove exactly what is going on with the vehicle.

+9
Albin Diagnostician
Leavenworth, Washington
Albin
 

Thanks for the very well detailed and very well thought out testing procedure

+1 Ð Bounty Awarded
Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Way way too long John. Any case study video should be five minutes max. Think about your target audience. Remember, anyone who misses something can just watch it again.

0 Ð Bounty Awarded
John Instructor
Beaver, Pennsylvania
John
 

Noted, but don't agree. Subsequent efforts on this subject can be shorter, but the only other way to cover that much information and build this foundation would have been to do multiple video's. I considered it but chose to keep this intact. Diagnostics doesn't fit into some a cookie cutter pattern, learning how to be good it doesn't either.

+3 Ð Bounty Awarded
Albin Diagnostician
Leavenworth, Washington
Albin
 

Great reply John, some things just need to be covered in their entirety

0 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

I think you're missing the boat Geoff. There are dozens of professional automotive diagnostic youtube channels that routinely post videos of 30 min or longer and these get thousands of views. I have watched many of them myself. 

There are many good ones but here are a couple that have some of the largest subscriber bases. There is a ton of quality stuff here but it's just the tip of the iceberg.

youtube​.​com/channel/UCtAGz…

youtube​.​com/user/ScannerDa…

+1 Ð Bounty Awarded
Geoff Diagnostician
Lahaina, Hawaii
Geoff
   

Missing what boat?

I have watched every video both of those guys have made. Watching Eric Obrocta bang on a ball joint for twenty minutes is not a diagnostic case study, nor is watching Paul Danner lecture on injector driver theory..

Long videos for the youtube audience at large and good diagnostic case studies are two different things. A good diagnostic case study is five minutes max.

With more and more videos being made every day, being concise and to the point are #1 in my book.

Edit edit edit!

0 Ð Bounty Awarded
John Instructor
Beaver, Pennsylvania
John
 

Hmmm. Five minutes. I'll give you all of the material that I have for the Nissan Frontier no start, no communication that I worked through last year. Let's see you produce a good diagnostic video for it that only runs five minutes. FYI. You'll have about twenty seconds for each issue. This was a lighthing strike that had two people into it before I got it and they only succeeded in adding more problems to it. 

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Nobody learns anything from a lightning strike repair except you shouldn't try them John. You would do a series of short ones for something like that. People making videos need to remember the rest of us are watching them in our SPARE TIME.

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John Instructor
Beaver, Pennsylvania
John
   

That's what pause and time stamps are for. One of the first things that had to be figured out was a code that was setting in the BCM for ignition switch power mismatch. The silver bullet answer to just that one problem was that the IPDM was fried (it was the third one that had been installed) because of a wiring harness connection error from one of the previous repair attempts. There is no way that I can envision a five minute video to instruct anyone on how to figure that out. It took walking through five separate issues to find the path to that and there was still ten more issues to address.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Yes, indeed, you have just proved it would NOT BE a good case study. Convoluted ridiculous fff-ed messes do not generally make good case studies. If it's far too big a mess nobody can follow along. In your case you could just title-splash "AFTER THREE FRIED IPDM, we found THIS" and you show where the wires were ruined by the last guy. Of course then you are just bashing another shop and that's not good for the trade, so once again it's not a good case study. Man made problems are always the hardest to find and you generally can't teach that skill. Good case studies give us the confidence, knowledge, and "virtual experience" that help get us to that next level, that we can go search and solve those advanced problems, out on our own.

0 Ð Bounty Awarded
John Instructor
Beaver, Pennsylvania
John
 

There were no wires ruined. A wiring harness had to be disconnected inside of the power distribution center in order to get the IPDM out. The body of one of the connectors for it was identical to one that actually plugs into the IPDM, and the two connectors were cross connected. If I do the video, it's going to have to show all of the vehicle issues noted on the first step of the examination. That was the loss of communication to specific modules, the codes in the BCM, and things like the power windows being inoperative. Then it would go into developing a strategy as to what to test first and why. There is a half an hour right there which leads to a half a dozen fuses blown, the BCM having all of the correct power inputs, the transmission control module fuse failing at key on and the IPDM being partially dead on top of the fact that there are three more of them in the car. (Both the first and second designs)

The IPDM connector issue never becomes apparent until PCM operation is examined. At that point it was already known that the ABS module was not communicating because of an issue with the data bus. The PCM was powering up but it wasn't able to communicate and wasn't commanding on the EFI relay in the IPDM, it was troubleshooting that failure that resulted in discovering the wiring harness issue. Once that was solved then the first part could be installed on the car, a new IPDM. Only then the process could continue for each additional failure.

The biggest reason to do all of this as one video and not a dozen little ones is trying to demonstrate that the entire process is dynamic. While different choices can be made as to what to check first you just don't usually get to see the logic behind the choices that the technician made if there was any. All too many times we have someone who will come along and say something like, "You should have checked that wiring harness connector first" or even worse if I do the video in little chunks someone will without any game plan just do that because they saw that's what the problem was on one of my videos. I could have done the video above in about two minutes if all you wanted or anyone needs is a silver bullet, but how much does that really help? The whole idea behind the video isn't that a clogged cannister will cause a cannister vent performance code, it is how do you really analyze the system by manipulating it during active testing. It's not about diagnosing just that one problem it's about being prepared to diagnose any problem with that system.

+3 Ð Bounty Awarded
Anthony Student
Hudson, Wisconsin
Anthony
 

John, couldn't agree more. you are targeting an audience that is particular to this kind of training. don't change a thing.

+2 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

John, your last paragraph here says it all. The important thing is not so much "what" fixed it but rather, how did you go about figuring it out.

Do you remember the Diagnostic Donut books by Bill McGrath? I still have one from the mid 90's and it was really a book full of silver bullets. At the time, they were very useful since cars of that era did suffer from a lot of pattern failures. However, as technology in the cars has advanced, the silver bullet method is less relevant. The most valuable skills today are not memorization but instead, logic and comprehension.

You need to be able to decipher service information, formulate a game plan, do the appropriate tests, analyze the results and then repeat as needed until the problem is found. That's why I love seeing how other techs diagnose difficult problems. I can always learn a new or different technique.

BTW, Bills books were very well done and usually included a lot of good tips. Ahhh, the good old days

+1 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

Personally I don't watch any of the ball joint type videos. I dislike it enough when I do it so i dont want to watch anyone else do it.

I pick and choose different diag videos because I like seeing the thought process employed in ferreting out difficult and intermittent problems.

I have definitely learned a few things from those guys and I can handle more than 5 minutes too. ;-)

0 Ð Bounty Awarded