[s-cars] Smog Check - high HC Level?

[Michael Wakefield]

With regard to the Engine coolant Temperature Sensor (G62), which is
located on the back of the head, the Audi Service Training Manual No
218 says: "Self-diagnosis recognizes two faults in the circuit of the
coolant temperature sensor, break/short to positive and short to
ground.  If the signal from the engine coolant temperature sensor
fails, and the air intake temperature is above 68 F, a fixed engine
coolant temperature of  158 F is assumed.  If the intake air
temperature is below 68 F, a fixed engine coolant temperature of 158 F
is assumed after three minutes of engine operation.  Adaption of oxygen
sensor control and idle speed control are stopped if the engine coolant
temperature sensor signal fails.  The evaporative emission system is
activated once the assumed engine coolant temperature of 158 F is
utilized by the Motronic engine control module."

The "adaption" sentence is especially of concern, although they don't
say what "sensor signal fails" really means.  Apparently it's pretty
important that G62 is functioning correctly.  I have no access to a
resistance vs temperature chart, but the Bentley says that at 68 F the
resistance between the two terminals should be between 1500-3000 ohms

MIke Wakefield
93S4

On Tuesday, April 15, 2003, at 10:10 AM, MLP wrote:

> Have you checked to see if your MFTS (multi-function temperature
> switch)
> &/or thermostat are functioning correctly.  From C Cohen's recent
> series of
> postings w/ regard to his S2 (below), and other prior threads on the
> list,
> it sounds to me like engine emissions are closely tied to, and greatly
> affected by running the correct temperatures.
>
> The adjustments have notable effects on gas mileage too ~ I believe
> some
> listers have reported changes in the order of 3 to 4+ mpg, just by
> getting
> the engine to operate at correct temperature levels!   Sounds like if
> you
> were idling long enough, maybe things finally got warm enough to get
> you in
> range.  What kind of gas mileage are you running?
>
> mlp
>
> -----Original Message-----
> From: Joe Petersack
>
> My 1993 S4 with 107K miles almost failed smog check. HC measured 84
> PPM, max
> allowable in CA is 100 and average is 17 under idle test.  tech had to
> run
> test twice to get it to pass.  One thing different this time was the
> car was
> idling for almost 30 minutes while they were doing other things before
> they
> actually ran the test.  Is this to be expected? Or should I start
> thinking
> about a new car converter?  O2 sensor was replaced at 80K. Joe
>
>
> -----Original Message-----
> From: ccohen5 [mailto:ccohen5 at compuserve.com]
> Sent: Monday, April 14, 2003 5:44 AM
> To: qlist; urq at audifans.com; Audi S Car List;
> Audi20V_Kruemmer at yahoogroups.com
> Cc: Frederic L'Huillier; Joern
> Subject: [Audi20V_Kruemmer] SQ problem ... solved
>
>
> It was the temp sensor at the back of the head!  Many thanks to all
> for some
> good advice.
>
> The old one was functioning but the tech could not tell if it was
> working
> within spec.  However some advice from Joern regarding its similarity
> to the
> 90/91 200, allowed me to extract some data from a Audi Training Manual
> for
> this engine which had the Ohm/temp spec for this sensor.  AUDIJIM
> found the
> sensor (a Baru equivalent of the Bosch OEM) item as well as the
> multifunction/fan sensor jic.
>
> The tech at Currys (VA) had tested the leakdown, fuel system and vacuum
> which all cam out ok.  He found after replacing the sensor that he
> still had
> to tweak the MAF.  now I do not know if he had played with this before
> he
> isolated the problem to the temp sensor and had to correct it.  By way
> of
> information, the first emission test run showed the idle at 250 ppm HC
> which
> was over the 200 ppm limit.  Just a half turn clockwise on the MAF adj.
> screw brought that down to the high 180s.  This was sufficient to pass
> the
> idle and 2500 rpm tests.  The cat is still not hot enough, but I am
> hoping
> that the next track visit will cure that.
>
> Idle and smoothness throughout the rev range are detectably better.
> Boost
> may be a little down from its 1.7 BAR spec with the leaner mixture and
> probably some Winter Gas.  So before I tweak it richer I am going to
> wait a
> few months.
>
> Colin
>
>
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