[s-cars] check engine light: officially bewildered

[chris chambers]

Mike,

I would operate under the assumption that the ECU can somehow sense
when the computer is plugged in/powered up.

Assuming this I would recommending reseting the ECU in order to purge
this learned behavoir.

Other than that I got nothin.....

Chris

 


----- Original Message ----
> From: Mike Fitton <rfitton at vt.edu>
> To: s-car-list at audifans.com
> Sent: Tuesday, September 15, 2009 10:49:44 PM
> Subject: [s-cars] check engine light: officially bewildered
> 
> Lemme start at the beginning.  Some may recall that I thought it would 
> be a good idea to hardwire a PC into my trunk.  So I did.  And then I 
> got one of those Chinese vag-com cables off ebay to do that sort of 
> thing.  I had it permanently plugged in and under the carpet.  Worked 
> great.  I could pull codes and scope sensors whenever I wanted.  All was 
> well.
> 
> At some point I needed to rearrange some of the wiring in the car.  Part 
> of that wound up seeing the cable unplugged from the computer for 
> several months.  And at some point my check engine light started coming 
> on.  Not sure on the correlation with that.  I left the USB side of the 
> cable in the glovebox so I could use it.  I kept plugging my laptop in 
> and wouldn't get any codes, yet the CEL remained.  I know that the light 
> without a code is usually a clear indicator of impending CPS doom, so I 
> replaced it.  Engine always starts as if the CPS is fine, before and 
> after replacement.  CEL remains.  No big deal, so I have a new 
> CPS...worse things have befallen me.  I continue to noodle on the CEL.
> 
> A couple days ago I finally get around to plugging the vag-com cable 
> back into the trunkputer permanently.  And now I notice that when I 
> switch the machine on, the CEL goes out.  When the machine turns off, 
> CEL comes back on.  And I don't mean in the Windows sense.  The light 
> seems correlated to when the USB port has power applied, basically 
> immediately after power-on while POSTing all the way up to power-off.
> 
> I'm confused as hell.  It seems that having the cable plugged into the 
> car but without a running computer on the other side causes the CEL to 
> come on, even if that computer were to be just staring at me with a 
> blinking cursor.  It didn't used to do this and I've never seen any VW 
> behave this way with any nationality of cable.  I guess I'll go out and 
> like reseat some connections or something, but um...any ideas?  Any 
> ideas at all?  Have I gone mad?
> 
> -Cheers!
> Mike
> 
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