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Sherlock Ohms

Chasing Down an Errant Engine Light

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jhmumford
User Rank
Gold
Re: Very good diagnostics, lots of effort.
jhmumford   3/12/2014 3:48:14 PM
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So, jlawton... in your earlier post, you were ranting against regulations that make vehicles more complicated and difficult to diagnose, as well as less reliable, but now you're admitting that the REAL problem is that the automakers have found a way to make diagnostics into a profit center by making it difficult for anyone but the dealer to diagnose problems.  Of course, in the given scenario the dealer had, without success, "fixed" the car without actually fixing the problem.  I have to admit that companies often try to keep some information proprietary so you are forced to use their dealers' service departments, but in this case it looks like the engineers simply didn't have the time to document all the possible cases that could result in the error code; the dealer simply replaced the most likely parts based on the engineering guestimate of the most likely failure modes. 

I wonder if the customer had returned the vehicle to the dealer a couple more times they would eventually have found the problem. This is why extended warranties are necessary these days; they force the dealer to actually fix the problem, and usually provide a loaner while they do it.

Of course the real problem is the burning of dirty fossil fuels to transport people around, when other alternatives exist, but I don't want to get into a rant or a flame war.

GTOlover
User Rank
Platinum
Re: Very good diagnostics, lots of effort.
GTOlover   3/12/2014 2:02:04 PM
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Not to be a tinfoil hat conspirator, but I believe the OBD specdifications were developed by the automakers as a means to enslave the auto-owner to the dealerships!

Totally agree jlawton, big government and crony businesses make good "legal" thieves for the little guys.

jlawton
User Rank
Gold
Re: Very good diagnostics, lots of effort.
jlawton   3/12/2014 1:57:08 PM
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GTOlover, your observation is interesting because both of the vehicles you mention are pre-OBD-II (happened in model year '96) so you clearly have experience with "company proprietary" interface software. I'm not expert in this field but certain brands (GM certainly among them) have made a bit of a "profit center" by intentionally "dunbing down" the so-called "public" interface and requiring GM-licensed tools to do the REAL diagnosis (and I recalll GM has been known to charge $50K/yr as an upfront "license fee" to anyone who even wanted to build diagnostic tools that could be used with GM vehicles). Also this problem is a classic ezample of a situation where a simple "code reader" isn't enough to resolve the issue, but it COULD have been if a code had been provided to "tie down" the problem a little better. I know there are many good reasons to justify the use of "proprietary tools" to assist in automotive troubleshooting, but the notion that in order to just keep my vehicle "on the road" if I don't have 100% confidence in my local dealer, I might need to consider the purchase of several thousand dollars' worth of proprietary "diagnostic tools" (which will only retain their value for a few model years anyway, not even long enough for ME to get full value out of them let alone sell them to recoup the price) hardly does much to endear me to the auto brands that employ this kind of strategy.

GTOlover
User Rank
Platinum
Re: Very good diagnostics, lots of effort.
GTOlover   3/12/2014 1:32:26 PM
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I cannot speak directly to the tools that this technician used, but as a shade tree mechanic, I have used my laptop with correct software and cables to trooubleshoot a 1993 Suburban problem. I have even used my laptop to run diagnostics on a 1984 Oldmobile. Assuming that the newer vehicles can output even more realtime data, the dealer should have the software and cables to properly monitor engine management parameters in realtime! The issue is probably training. And as you point out, this is not well covered in ASE classes!

lynnbr2
User Rank
Iron
Error Loops
lynnbr2   3/12/2014 12:46:20 PM
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This article also displays the typical "time crunch" design engineers are under to complete their projects. Usually too little time is spent on error loops, most of the time is spent verifing the system works properly within its range of "normal" conditions - when things are actually normal.

There could have been a diagnostic manual that explained that the air injection circuit could cause a O2 lean condition, but no, not enough time to document that. So, the maintenance guys suffer, but the sales guys are happy....

bob from maine
User Rank
Platinum
Re: Very good diagnostics, lots of effort.
bob from maine   3/12/2014 12:45:50 PM
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I'm impressed! I wonder what diagnostic instrument permits that level of analysis. I've watched dealers amass thousands of dollars of customer debt trying to troubleshoot an intermittent problem and I've never seen a scanner or analyzer with pre/post trigger storage capability of that depth. I have done some CAN buss analysis of other systems and am truly amazed at the comlexity of modern automobiles. Most mechanics have a good basic understanding of how an engine management system works but the described level of analysis is way beyond anything I've ever seen taught at any major marque training session or ASE accredited school. Nice article.

William K.
User Rank
Platinum
Very good diagnostics, lots of effort.
William K.   3/12/2014 10:43:54 AM
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Interesting post and quite an indication of how only knowledge plus understanding can provide good troubleshooting. It also points out how incredibly complex engine control systems have become in the constant effort to run within ever tightening emissions standards. It does demonstrate all of the problems that arise with a slightly inadequate engine disgnostics program. Justadding a timer to the limits checking loop would have prevented the problem of th false indication.

jlawton
User Rank
Gold
Re: Excellent example of troubleshooting
jlawton   3/12/2014 10:00:53 AM
Of course it's excellent troubleshooting. It's also an excellent demonstration of the weaknesses of the diagnostic system as it exists, since these codes are almost completely "devoid of context" so the service technician has to run movies and all these additional processes to try and extract the correct information, provided he's even trained well enough to know BOTH what to look for and how to find it! It's also absolutely disgusting that the laws in the state I live in will deprive the car owner of the ability to register his vehicle if this code is inclined to appear during smog testing, and the "punishment" for owning the misbehaving vehicle is to pay the $65/hour or more shop rate until either the heavens open up and disgorge infinite wisdom on the shop technician, or until the owner loses his patience with both the cash drain and the loss of his basic transportation, and goes down the street to trade his nearly-perfect vehicle for an entirely new set of problems! And the system complexity required to achieve the ever-increasing utopic CAFE rate goes up each year because the owners of these vehicles with their "evil" carbon-fuel-consuming, carbon-dioxide-"pollutant"-emitting internal-combustion engines simply refuse to trade them in on electric vehicles that run on energy supplied by wind and solar power that doesn't exist, isn't economically feasible and never will be, but you'll never convince the tree-hugging utopian liberal politicians who pass these laws because the vehicles that provide THEIR transportation have been chauffered for them for decades - most likely at the taxpayers' expense too! (I can't help thinking if these folks weren't such total "deadhead ideologues" the condition in question would be provided as simply "warning status" and allow us to just get on with our lives, but if I've learned NOTHING else it's that these pampered elites will never allow reality IN ANY FORM to distract their utopian vision, provided as it is at OUR expense rather than theirs!)

didymus7
User Rank
Platinum
Excellent example of troubleshooting
didymus7   3/12/2014 9:08:18 AM
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David Agans' excellent book 'Debugging' has rule #1:  Understand the System.  Here, understanding the system was paramount to solving the problem.  Mark Hicks displays all the necessary skills to track down the problem.

My experience has been that most technicians in dealer's service centers are '6 week wonders'.  They are given a couple of weeks of training and then flung into jobs without any mentoring, or, in most cases, any understanding of how to find the cause of a problem.  Here the dealer doesn't come close to finding the problem, when, by any measure, they should have been the final authority.

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