[kwlug-disc] OBD-II/OBD2 Diagnostic Scanner

CrankyOldBugger crankyoldbugger at gmail.com
Fri Mar 7 13:06:20 EST 2014

Well, in all of this good discussion on car parts, I heard somewhere in
there that they won't pass an e-test if the check engine light is on?  This
is troubling as my light has been on for years and I'm due next month for
new plate stickers.  None of the mechanics I've seen can figure out how to
turn the light off and keep it off (they can reset it, but it comes back on
a week later).
Does anyone have an idea of how I can resolve this?

On 7 March 2014 12:18, John Johnson <jvj at golden.net> wrote:

> On 2014-03-07 11:32, Chris Irwin wrote:
>> It's amazing how long this technology has been sitting around in cars,
>> though. I just bought a bluetooth adapter for my 1987 Fiero, (it pre-dates
>> ODB-II, and doesn't work with my existing adapter). I haven't used it yet,
>> though.
> As a kid in the 1960s I got hold of a wiring diagram for a car, maybe my
> father's. Even without an ECM the car had built in diagnostics. If one is
> familiar with the cars of the day, when starting, the dashboard 'idiot'
> lamps should light up in a particular patter, if all is well. IIRC With the
> ignition on but before cranking the starter the oil lamp would come on. The
> Oil lamp would go out while cranking but the Alt light would come on. When
> the car started both the Oil lamp and the Alt lamp would go out. The patten
> that these lamps (and others) would follow, during starting and at other
> times, would give an indication of the health of other systems not just the
> area associated with their labels.
> A 1970s Volvo had an 'idiot' light that would give an indication if a
> headlight or taillight was out. It would do this with a circuit that would
> compare the current in the light circuit on the right side of the vehicle
> with that on the left. And if there was an imbalance, light the 'idiot'
> light. The circuit was comprised of a reed switch inside two coils. The
> right side current would flow through one coil. The left side current
> through the other. The coils were arranged such that the generated magnetic
> fields would cancel each other out if all was well. If all was not well,
> the resulting magnetic field would activate the reed switch lighting the
> 'idiot' lamp. (Aside: A similar differential measurement is used in
> electrical ground fault monitors.)
> Some early ECM / OBD systems (circa 1980s 1990s) had a mechanism where a
> trigger action, like connecting a wire on the diagnostic plug, would cause
> one of the dashboard lamps to flash in pattern that indicated the codes.
> One would need to have a good eye to count the flashes to determine the
> code. At the same time, codes would be signaled on another connector in the
> diagnostic plug where one could connect a voltmeter. And one could count
> the swings from 0V to 12V. Again, one would need to have a good eye to
> count the voltmeter swings to determine the code.
> And while I am writing this, I will toss in a personal trick, learned
> while trying to maintain old cars. To distinguish between electrical
> problems cause by a possible failing battery and a possible failing
> alternator I would, sometimes use the radio. I would set the radio to the
> AM band and tune it off station. If the audio sounded like a 'motorboat'
> them there could be a failing diode in the regulator circuit in the
> alternator. (The term 'motorboat' is commonly used in these situations.)
> With a degree of certainty, I would pull the alternator and take it to the
> Parts Source (shill intended) and use their free diagnostic system to
> verify my findings.
> Attn: Kwartzlab members: The KWLUG list has a good thread on OBD-II/OBD2
> diagnostic tools.
> And in the thread a DIY solution has been mentioned.
> Regards
> John Johnson
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