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A Mechanic's Life - Tales From Under the Hood

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  • thecardoc3thecardoc3 Posts: 1,656
    Yes, I remember it. The link was the owner of that car instructing another driver about how to drive through wheel shake. :shades:
  • steverstever Viva Las CrucesPosts: 41,992
    What is the next step and why?

    Go to the Chevy dealer and buy an OEM gas cap and quit using aftermarket ones from the auto parts stores. :D

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  • thecardoc3thecardoc3 Posts: 1,656
    Go to the Chevy dealer and buy an OEM gas cap and quit using aftermarket ones from the auto parts stores.

    All kidding aside, that of course would have only cost the owner more money and you just added yourself to the list of people who failed to give this owner an answer, the first time that you looked at the car.

    This is a real case study, either you know the correct proceedure to diagnose the car, or you don't.
  • steverstever Viva Las CrucesPosts: 41,992
    edited December 2012
    Although, per forum posts here over the years, that option has "fixed" quite a few recurring CEL problems for people.

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  • thecardoc3thecardoc3 Posts: 1,656
    Although, per forum posts here over the years, that option has "fixed" quite a few recurring CEL problems for people.

    That mistaken belief is one of the reasons why I (or at least someone who really does know better) should have been around here a long time ago.
  • steverstever Viva Las CrucesPosts: 41,992
    edited December 2012
    It's pretty simple from the point of view from the other side of the counter.

    The most common reason for a CEL coming on is a loose gas cap. If tightening that doesn't work the next step I'd take is to get on the net and find the bad cap and O2 sensor posts. Then I'd go buy an OEM gas cap. If that doesn't work, I'd take it back to the dealer and get my money back (less a 20% restocking fee perhaps). So far I'm out my time and maybe $4 and some gas or shipping costs). Big whoop. If it works I'm golden.

    If the easy stuff fails I look for real help (since 02 sensors can be pricey and typically can't be returned as easily as non-electrical parts).

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  • thecardoc3thecardoc3 Posts: 1,656
    Then I'd go buy an OEM gas cap. If that doesn't work, I'd take it back to the dealer and get my money back (less a 20% restocking fee perhaps)

    So then if they try to sell it to the next person and they realize that it's already been enjoyed once by someone else and they get upset because they have been sold a "used part" instead of a "new one". In that customers eye's someone is being a theif and ripping them off.

    It's pretty simple from the point of view from the other side of the counter

    Yea, you might just as well keep the new cap and out your old one back in the box to return.... That's how it would look to another customer on your side of the counter. That's how it would look to you if you opened the box and found the cap you just bought had already been tried.

    In real numbers, barely 1% of evap failures are caused by faulty gas caps, claiming anything else is intentionally misleading to the consumer. Now why would you want to do that?

    Loose caps are caught by the systems because today they run a specific series of tests that are triggered by an increase in the level in the fuel tank.

    You have said numerous times that you want the cars to be able to 'self diagnose" more completely and to a certain extent that has happened. They have managed to make it pretty cut and dry how diagnostics should be performed and just how obvious blind guesses by untrained individuals are nothing more than that.

    Feel free to admitt that you have no clue about how to really approach this anytime. The sad part is, what I use is a very simple, repeatable routine that has a technician arrive at the correct answer THE FIRST TIME, and EVERY TIME, no matter where the failure is. Guess you should be able to see why it was somewhat refreshing to have had a customer that was glad we were there to help him.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,687
    (Any ideas why I mentioned that right here?)

    Make assumptions that something isn't a problem because it was already tested/replaced, and you're going to make the whole process that much more difficult for yourself.

    What is the next step and why?

    Assuming an understanding of the system (which you noted as step 1), I'd say that the next step is to replicate conditions that should cause that DTC to set, in order to verify that the OBD system is working correctly.

    How would you proceed with testing this system to repair the problem?

    Then, I'd test the parts of the system that fed into it to determine which part(s) was(were) out of spec.

    Sorry, but since I haven't a clue how that system is looped, I can't get any more specific than that.

    ---

    I'm curious about two things (in addition to your general solution methodology & the actual problem in this case): 1. How long did it take to diagnose, and then fix, the issue, and 2. Appx. much did the customer end up paying?

    I'm glad to hear that the customer was appreciative in this case. He tried the other method, failed, and knew it was time for something better! :shades:
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • steverstever Viva Las CrucesPosts: 41,992
    edited December 2012
    I take "used" stuff back all the time and store repackage and resell it all the time. Go in to the back of most any store and you'll see a shrinkwrap machine they expressly use for this purpose. Bit of a red herring issue; if a parts store doesn't want parts returned, they can post a sign and not accept returns, and check boxes when they do take returns and make sure the part isn't scratched and dinged.

    In real numbers, barely 1% of evap failures are caused by faulty gas caps, claiming anything else is intentionally misleading to the consumer. Now why would you want to do that?

    In the real world many CEL lights come on because of loose gas caps. A $20 exercise at AutoZone or NAPA is cheaper than going to the shop.

    If a customer called you and said their CEL was on but they couldn't stop by your shop for 3 days, would you tell them to check their gas cap and perhaps ask them when someone last filled up the car?

    (As an aside, did you see where the most recent Ford recall for potential engine fires is going to be addressed by a software fix?).

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  • thecardoc3thecardoc3 Posts: 1,656
    I take "used" stuff back all the time and store repackage and resell it all the time

    Many returned items never make it back to a stores shelves. Too much of a risk of dissapointing the next customer. These items need to be sent back to the manufacturer who can inspect them, and then they must use another routine to re-release them or else just scrap them.

    In the real world many CEL lights come on because of loose gas caps. A $20 exercise at AutoZone or NAPA is cheaper than going to the shop.

    Not anymore they don't. My 2002 Ford Explorer has a check fuel cap light that is seperate from the check engine light. When you refuel that car (and many others just like it) the computer runs the large leak test and compares that result to stored test results from previous tests. The system then knows for certain if the newest result is different from previous test results and in the case of my Explorer would turn on the loose cap light and not store a pending code for the evap system. Now the next time the test runs and it detects a leak, then the system stores the pending code. Then only after the third time the test would find a leak it sets the gross leak code and now turns the light on.

    Cars not equippped with the loose cap light set a specific code for a large leak, seperate from the SAE code and again it's because of weighted testing results that are compared to previous tests.

    If a customer called you and said their CEL was on but they couldn't stop by your shop for 3 days, would you tell them to check their gas cap and perhaps ask them when someone last filled up the car?

    No. The questions that I am going to ask are:
    Is the car running normally? Are you having any trouble with it running rough, stalling, difficult to start or is or has the check engine light been flashing?

    The moment someone touches the cap once the light has come on, the only thing that they really accomplish is make it impossible to prove if the cap's being loose caused the light to be on. To a technician it ends up being an intermittent failure condition and you can only assume the cap must have been loose, you don't actually know for certain if it was or was not.

    By touching the cap, and now we get a "no trouble found" it's quite common for the light to come back on within the next few weeks and now it's "a second trip back to the shop" because they didn't fix it the first time.

    BTW, with some cars that have ORVR (on-board refueling vapor recovery) systems you can leave the cap completely off and it doesn't care because the filler neck is sealed off down below closer to the tank. Cars that test themselves with pressure cannot test the filler neck with an ORVR system and it makes for a nice little puzzle for the technicians when I do as a hands on portion of an evap class that I teach. We make the monitor run with the gas cap off of the car and it passes. This does not work with cars that use vacuum to test themselves, they will catch the cap loose/missing.

    As an aside, did you see where the most recent Ford recall for potential engine fires is going to be addressed by a software fix?.

    No, haven't paid any attention to that at all. First we don't do recalls as an independent. The reflashes that we do but are totally software driven and pretty much a hands off operations outside of telling the computer yes, do the reflash and then exercising the ignition switch as the system commands.
  • thecardoc3thecardoc3 Posts: 1,656
    Assuming an understanding of the system (which you noted as step 1), I'd say that the next step is to replicate conditions that should cause that DTC to set, in order to verify that the OBD system is working correctly.

    In a round about way that is correct. The code sets because the computer seals the system by closing the cannister vent valve and then opening the purge valve in order to pull the system into a vacuum. (about 8"-12" in water) Then the purge valve is then turned off and the computer watches the vacuum bleed up rate. By knowing the fuel level, and therefore how much space is air/vapor in the tank it can calculate if the bleed up rate is excessive (leak detected) or not (system sealed).

    So the first step is to command the vent valve closed with the scan tools bi-directional 'controls. The vent valve will make an audible "click" when it opens and closes.
    The Cobalts cannister vent valve could not be heard to be closing/opening.
    That means the system cannot test itself. Two questions need to be thought of and then proven/disproven at this time.
    If the problem is electrical, why isn't there a code for the vent valve's circuit?
    The customer (allegedly) already replaced the vent valve so does that mean it's a mechanical issue with the "new" valve?

    With these two questions in mind it's time to do pinpoint testing on the vent valve and it's circuit.

    The purge valve is tested in a similar fashion, first command it to operate with the engine off and simply listen for it. If you cannot hear it, then specific testing for it, and/or it's circuit is required. If you can hear it then you need to start the engine and see if you can control the vacuum to the system. The Cobalt's purge valve passed these checks.

    1. How long did it take to diagnose, and then fix, the issue, and 2. Appx. much did the customer end up paying?

    The time to locate the exact failure was about half an hour, the time to actually repair the wiring harness damage that I found was about an hour, including doing the post repair testing that was required to make sure that the car would then pass it's monitor the next time that it ran. Our diagnostic/electrical labor rate is $115/hr. People often gasp at that but in reality a shop hanging brakes or doing suspension work or exhaust is realizing more profit per hour than we are with that diagnostic rate and they don't have to spend a dime to do that kind of work they way we do with scan tools, software and schools.

    1.5hrs at $115 with the sales tax and he was out the door with the car working correctly for about $185. Consider that he had already spent over $400 while failing to fix this over the last year.

    Now one of the things we don't do is go on a treasure hunt on the cars. I don't go over the whole car trying to find a grocery list of services to sell. We go straight in at the problem that the car came in for, and straight back out. I wouldn't be able to keep a job at a chain store working like that, I wouldn't be selling enough to keep the management happy.
  • steverstever Viva Las CrucesPosts: 41,992
    The moment someone touches the cap once the light has come on, the only thing that they really accomplish is make it impossible to prove if the cap's being loose caused the light to be on. To a technician it ends up being an intermittent failure condition and you can only assume the cap must have been loose, you don't actually know for certain if it was or was not.

    Heaven forbid if I need to get to your shop and I'm two hours away and my fuel light just came on too. :shades:

    The Escape recall was interesting to me because the only other reflash fixes I remember had to do with driveability issues, like shift points. Being able to reduce the risk of an engine fire with software is a pretty good trick and illustrates how the new cars aren't your father's Oldsmobile.

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  • qbrozenqbrozen Posts: 17,708
    Our diagnostic/electrical labor rate is $115/hr. People often gasp at that

    Hell, that's cheap compared to a BMW dealer.

    I didn't get to answer your question originally, but I did just go through this on my volvo. Its a '98 and I've already had extensive experience with another '98 some years ago. Code was the massive evap leak. First thing I did was go to the dealer and buy a gas cap because, in my experience with this car, it is what was stated above: the most common issue.

    Cleared the code and drove for about 5 days before it came back. There are 2 more common things on this car. One being the purge valve and the other being clogged vent. Before testing the valve, I decided to get underneath and inspect the vent. No clog. But then I inspected the canister and after removing some brackets in the way, I found a split air line. Removed, trimmed, reinstalled, and cleared the code again. So far so good, but I'll want to see a couple of weeks without a light before I feel I've solved it.

    Now, I know you aren't happy with my process. Should I have jacked up the car and gone through the whole troubleshooting first? Maybe some people should. But if $24 for the gas cap saved me the 30 mins I spent on fix #2, it would have been worth it to me. And, certainly, $24 total spend is a helluva lot less than a professional shop diagnostic fee. And, no, I'm not returning the cap because I know it to be such a common failure point that I might as well keep this one and know I'm good for about 4-5 years.

    '13 Stang GT; '15 Fit; '98 Volvo S70; '14 Town&Country

  • xwesxxwesx Fairbanks, AlaskaPosts: 8,687
    he was out the door with the car working correctly for about $185.

    That's a great deal for him. Plus, he's a happy customer that will be back (but only when another problem comes up that stumps him). If I could have found a local mechanic that could solve my '96 Outback's issues a decade ago, I would have stumbled over myself trying to get to that place! As it was, I spent around that same $400 for no resolution at all.

    Also, thanks for sharing more information on the process - it's very interesting stuff and clearly illustrates the investment required (time, tools, and education/training).
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 46,007
    Where I live common labor rates are at $140/hr now. I'm fine with that, if they are efficient AND correct.

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  • srs_49srs_49 Posts: 1,394
    ...to actually repair the wiring harness damage that I found ...

    So, what caused the damage to the wiring harness?

    And didn't you tell us about another problem (SUV liftgate?), that people were throwing BCMs at and that turned out to be a wiring harness issue?
  • thecardoc3thecardoc3 Posts: 1,656
    Cleared the code and drove for about 5 days before it came back

    Snip

    Now, I know you aren't happy with my process. Should I have jacked up the car and gone through the whole troubleshooting first? Maybe some people should

    If there is something that I'm not happy about it's the fact that there are those who keep claiming that all someone has to do is tighten or replace a fuel cap for an evbap issue when what you have here is the reality, the caps rarely fix the evaporative system problems. .
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,687
    *sigh*

    As we talk about the complexity of modern cars and all these systems they have, I still can't help but appreciate how "clean" cars operate today. Last night, I used my plow truck ('76 F250) for about an hour clearing mine and my neighbors' driveways along with our cul-de-sac. I had my coat, boots, gloves, and hat donned at the time.

    This morning, when I put on my coat to go to work, it still smelled like "old truck." You know, that mixed fume smell that only an old vehicle can create. ;)
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • qbrozenqbrozen Posts: 17,708
    the caps rarely fix the evaporative system problems

    I can't speak for all makes models. I only know what I know, which is a cap solved exactly the same code on my last '98 S70, as well as the same code for dozens of other owners.

    I would never claim that to be the fix for any other make/model unless I knew it to be a common problem for that car.

    '13 Stang GT; '15 Fit; '98 Volvo S70; '14 Town&Country

  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,549
    The cap has been the problem on my leSabre 3 times over 8 or more years. Each time cleaning the o-ring and the mating surface, lubing same, and reinstalling then waiting for the car to have the requisite conditions to run the check for leaks showed the problem had been solved.
  • steverstever Viva Las CrucesPosts: 41,992
    Even if the cap is the problem in only 1% of the cases, with 300 million cars on the road, that's still pushing two million cars (even after throwing out ~100 million older ones that may not be OBDII cars - like Xwes's lol).

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  • xwesxxwesx Fairbanks, AlaskaPosts: 8,687
    Hey now, don't make fun of my old beast(s)! :cry:

    -Wes-
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • steverstever Viva Las CrucesPosts: 41,992
    OBDII came out in 1996. My Subie made the cut with a few months to spare. :D

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  • thecardoc3thecardoc3 Posts: 1,656
    Replacing the gas cap first failed to fix 100% of the cars that have had an evaporative emissions issue that then had to be taken to a shop to be properly diagnosed and repaired.
  • thecardoc3thecardoc3 Posts: 1,656
    OBDII officially came out in 96. Honda drug their feet and got in trouble with some of the vehicle systems. Some manufacturers like GM and Ford actually had the systems on the road as early as 94, they just didn't call it OBDII.

    Evaporative systems didn't need to be fully enhanced fleet wide until 99. The non enhanced systems couldn't test for leaks, and only had to prove that they could/would purge.
  • srs_49srs_49 Posts: 1,394
    Replacing the gas cap first failed to fix 100% of the cars that have had an evaporative emissions issue that then had to be taken to a shop to be properly diagnosed and repaired.

    Think about what you just said - "...that then had to be taken to a shop to be properly diagnosed and repaired".

    So what you're describing is a limited subset of the total population of cars that have had evaporative emissions issues - that is, those that were brought into a repair shop.

    If the total number of vehicles that experience an evaporative emissions failure is 100, and replacing the gas cap solves the problem in 90 of those cases, but doesn't in 10, those 10 are the ones you or someone else is going to see in your shop. So from your or some other shop's experience 100% of the cars (that you diagnosed and repaired) needed something other than a gas cap replacement. You (or some other shop) never see the other 90 cars.
  • steverstever Viva Las CrucesPosts: 41,992

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  • thecardoc3thecardoc3 Posts: 1,656
    Experience has proven that what you linked fails to fix the cars, the majority of the time. It is a lack of knowledge and experince that has you clinging onto your perception that a gas cap being loose or bad is the most common cause for evap issues.

    It's almost funny how you are ignoring what it really says.

    Possible Solutions With a P0442, the most common repair is to:

    •Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
    •Otherwise, replace the gas cap, or
    •Inspect the EVAP system for cuts/holes in tubes/hoses


    By far the "most common" repair is a close tie between the filler neck corroding and leaking, and the vent valve failing to seal for one reason or another so the car simply cannot test itself. Why is it that your link doesn't mention either one of those? That's what you get when someone who really doesn't know anything about how the system works, nor how they fail, and yet they still try to give people advice.

    In many way's it's similar to an instructor, VS a teacher who each are presenting a continuing educational class for auto repair. You can take the greatest teacher in the world, and while he/she may do a great job teaching if they have no idea that the material they are trying to present is flawed, that makes the training, just like your link be worthless. It takes a truly qualifed instructor, who knows how to do the work to recognize when there are flaws in the material and he/she must correct it so that the educational material is worth the techs time to attend.

    Is there a reason why you don't want consumers to understand how the cars really fail, and what it takes to diagnose and repair them, correctly?
  • steverstever Viva Las CrucesPosts: 41,992
    edited December 2012
    I know you don't see many new cars since you don't do warranty work, but I doubt that many 2012 models with the CEL on throwing a P0442 have corroded filler necks.

    Well, up here in the UP, it's a definite possibility. :shades:

    [Edit] This is good timing. Check out this cry for help over in Edmunds Answers. A 2005 Ford Five Hundred throwing P0442. Place your bets. :shades:

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  • thecardoc3thecardoc3 Posts: 1,656
    Take note of the enabling conditions for the onboard computer to run a P0442 test. Especially note the line I highlighted in BOLD

    Conditions for Running the DTC

    IMPORTANT:

    The following conditions must be met prior to ignition OFF.

    •Before the ECM can report DTC P0442 failed, DTCs P0446, P0455, and P0496 must run and pass.
    •DTCs P0112, P0113, P0116, P0117, P0118, P0120, P0125, P0128, P0443, P0446, P0449, P0452, P0453, P0463, P0503, P1106, P1107, P1111, P1112, P1114, P1115, P1516, P2101, P2108, P2120, P2125, P2129, P2138, P2610 are not set.
    •The diagnostic runs once after a cold start drive cycle.
    •The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
    •The start-up engine coolant temperature (ECT) is less than 30°C (86°F).
    •The start-up IAT and ECT are within 8°C (15°F).
    •The barometric pressure (BARO) is more than 74 kPa.
    •The ambient air temperature is between 2-32°C (36-90°F).
    •The engine run time minimum is 10 minutes.
    •The vehicle has traveled more than 5 kilometers (3 miles) this trip.
    •The ECT is more than 70°C (158°F).
    •The fuel level is between 15-85 percent.
    •The ignition is OFF.
    •A refueling event is not detected.
    •DTC P0442 runs once per drive cycle when the above conditions are met.
    •One test occurs at ignition OFF after a drive cycle, and may require up to 45 minutes to complete. No more than 2 tests per day are allowed.
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