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Sherlock Ohms

Chasing Down an Errant Engine Light

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Amclaussen
User Rank
Platinum
Re: Excellent example of troubleshooting
Amclaussen   5/28/2014 1:47:39 PM
Well said...

I call them "Eco-Illogical" politicians. Their pride resides in their enormous capacity to inflict more damage than they can prevent (if any). Most of them pululate in European countries, have caused much damage as they like to prohibit a lot of things, all "in the name of the ecology". Take the damn prohibition on incandescent lightbulbs to increase the sales of their favorite replacement: the Compact Fluoroescent Lightbulb, that causes more ecological damage as those contain sizable quantities of mercury (convenently hidden from public knowledge, as mercury de-contamination of a single room is very expensive...). They also perform poorly when connected to dimmers, or placed inside non ventilated enclosures; they also produce a lot of contaminant garbage when their shorter than promised life ends up, and demand more valuable materials to be fabricated. Or look at the much increased failure rate of all kind of electronic devices that now must use "lead-free" solder, again producing much more electronic garbage than when industry used old reliable Tin-lead solders. I've seen more than enough cars displaying false "check-engine" troubles that simply do not exist and the vehicle still perfectly meets its emissions, frequently at levels well below the legal limits. It is more of a justification to show overly "green" people and tree-huggers that they are working hard to "save" the planet. Many measures impossed by those arrogant politicians are truly counter-productive, like the badly under-used bus lanes that only are traveled by "ecological" buses less than 5% of the time, but prevent common drivers to use them, which produces terrible traffic congestion and heavily increases the total emissions, a complete non-sense!.  Frequently, some cars manufacturers give some of their electric models to these corrupt politicians, which become ardent proposers of that technology, and then start to lie to people about the real total emissions from their whole life-cycle, often completely ignoring the emissions produced during manufacturing, disposing of and recycling of batteries, which falsely make their use as a completely "Zero Emissions vehycles" which is false of course. And the recent prohibition directed at one automaker from using a proven refrigerant in order to impose a newer "greener" one that resulted in more serious risk of fire for the vehycle occupants... all in the name of ecology!

OLD_CURMUDGEON
User Rank
Platinum
Re: I CAN'T FIND IT!
OLD_CURMUDGEON   4/24/2014 8:34:52 AM
NO RATINGS
The main reason I made that comment was because I had the blog set for THREADED mode, and I read the lengthy discussion between two of the bloggers that quickly degenerated into a political argument without due cause as far as I'm concerned.  There are forums for technical discussions & exchanges of ideas, AND there are forums for political debate.  But, I don't believe these lines have to cross, especially in this DESIGN NEWS arena.

warrens60
User Rank
Iron
Looking for suggestions
warrens60   4/24/2014 3:03:49 AM
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Really great and timely set of comments. I have a 2001 Saab 9-5 with a turbo 6. It has painfully been doing a similar thing that Mark described. Almost word for word with exceptions as noted. It has been in the shop several times to fix the trouble light codes.

A couple of variations, if I drive the car at higher RPM, such as in 3rd at speeds of 45-50 and RPM around 2k, the inevitable P0181 code takes longer to show up.

Another issue is a rare P0420 that shows up. About the time this shows up, the car runs rough at startup and then does a dieseling thing after being turned off. The typical run time is about 10-15 minutes. The sequence is after running the car for no less than 10-15 minutes, i stop the car, place it in park, turn it off and the engine diesels for 5-8 seconds.

I thought that the new engines had anti-dieseling soilenoids. Correct me if not all do.

The car runs OK (not in limp mode) however, the milage is terrible. 

Most of my travels occur in town with speeds of between 35-55 mph for 15-20 minutes. 

If I travel on the highway, at speeds of 65-70, I can travel for hundreds of miles without one trouble light issue. 

Suggestions are much appreciated?

dnason@kicmail.com
User Rank
Iron
You may have solved my problem!
dnason@kicmail.com   4/23/2014 4:51:36 PM
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Generally a 171/173 code combination (lean bank 1/lean bank 2) code indicates a vacuum leak as it did on my wifes 2004 and was solvable with a new o-ring.

Since buying a 1996 motorhome last summer with a Ford E-360 chassis we have had a random pair of these codes with no symptoms and taking anywhere from 20-200+ miles before it triggers. When we first looked at the vehicle the light was set but the seller got it to pass smog by fixing something that was 'sticking' but I never found out what it was. After reading your post, I am going to stop looking for vacuum leaks and focus on the smog solenoids because maybe that's the problem.

Thanks for the great idea!

cwoodhouse
User Rank
Silver
Re: I CAN'T FIND IT!
cwoodhouse   4/23/2014 3:59:56 PM
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Ha Ha!

Fibber
User Rank
Iron
Re: Very good diagnostics, lots of effort.
Fibber   4/4/2014 12:49:18 PM
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A couple of things come to mind after reading this.  The author clearly understands the complex system.  Bravo.  The OBD-II standard dictates that we shall have clean air, and a bunch of systems that must be monitored for compliance.  Exactly how the auto maker chooses to attain this is largely up to them.  The current standard dates to 1994, (first implemented around 1996) and has a unified list of a few hundred codes.  20 years later auto manufactures have thousands more proprietary codes as they monitor things never dreamed of back then.  It's really time for OBD-III. 

1) Shortly after the fuel system goes into closed loop, at a steady state speed and when other conditions are met the Catalytic Efficiency Test is conducted.  On my cars this is typically around the timeframe you called out – 8 minutes after a cold start.   At that time the mixture is by program intentionally cycled rich for a period and then lean.  The front A/F sensor is ignored, and the rear sensor monitored to see if the cat bed can hold enough oxygen to maintain clean exhaust.  If it fails two successive drive cycles you get a P0420.  While reading your description the first thing that came to mind was that the ECM wasn't ignoring the feedback of the front (A/F) sensor and was flagging the lean output as a problem. 

2) Good catch on the air pump!  I understand the use of air injection to increase the oxygen content in the exhaust stream and speed the reaction driven heating of the catalyst bed.  This is particularly important during the open loop operation when the engine is cold.  But putting it prior to the A/F (the air fuel upper oxygen sensor) really is a flawed design.  Once the engine goes into closed loop operation (the mixture is solely regulated by that sensor) there shouldn't be anything that it could ever see other than combustion chamber exhaust output – under any circumstances.  Yes, I know it's always been done this way, relying on the solenoid valve as an engineering control to prevent this conflict. But there's certainly a better layout.

OLD_CURMUDGEON
User Rank
Platinum
I CAN'T FIND IT!
OLD_CURMUDGEON   4/3/2014 8:13:50 AM
NO RATINGS
 

Does anyone know where the OBD II plug is on my 1957 Chevy Bel Air w/ the 283 cu in engine?  I've looked all around under the hood.  I even looked in the glove compartment & I couldn't find anything there either.

Cabe Atwell
User Rank
Blogger
Re: Very good diagnostics, lots of effort.
Cabe Atwell   3/26/2014 4:42:48 PM
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Another great piece! I find it amazing as well, that such a short post brings about a heated debate.

GTOlover
User Rank
Platinum
Re: Very good diagnostics, lots of effort.
GTOlover   3/13/2014 12:43:46 PM
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bob, you are technically correct.

http://www.epa.gov/obd/index.htm

It was SAE and ISO the standardized a lot of the physical and codes used in modern vehicles. What was interesting about this debug was the tools used by this technician was not the simple parts store code reader. The idea of reading codes and diagnosis of a problem would seem to part and parcel for the dealership. But time and time again, I read of stories of people going to the dealer getting soaked for some 'mechanic' to swap out enough parts until the problem goes away. It matters little if they continually beat the standard rate if the part they replace was not the faulty component!

And if this is warranty work, how is this helping the engineers from identifying components that need to be re-designed for more robustness? All the parts seem to be junk if the tech at the dealer is changing everything they can think of to make the light go away. Now if an engineer got this troubleshooting report, he could look at revising the code (as suggested by others) or visit the air valve solenoid to see why it might be sticky.

bob from maine
User Rank
Platinum
Re: Very good diagnostics, lots of effort.
bob from maine   3/13/2014 11:12:28 AM
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I thought the OBD programs were mandated by the Government. I do know that many manufacturers have proprietary software to enhance the 'normal' OBD diagnostics. I do have a fairly decent scanner and it does not have the memory to capture a significant time window BEFORE and AFTER a triggering event. Most scanners offer either a fault tree starting with a specific code, or they offer an off-line search with a fault-tree: neither of these would permit the detailed analysis described. At $100/hour with mechanics getting paid based on a flat-rate book, there is no incentive for the mechanics to troubleshoot. A good mechanic can beat the 'book' by 3 or 4 to 1, so like a lawyer, can actually bill a hundred hours in a 40 hour week - no time in that schedule for detailed troubleshooting. Intermittent problems are the bane of a mechanics life - often call-backs must be performed at no cost to the customer unless it can be shown to be the service writers misdiagnosis or something.

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