[Vwdiesel] *CEL light on middle of road trip*

[James Hansen]

Only way the ECU has to detect EGR flow is to detect a drop in the MAF
measured flow.  When the EGR valve opens, the ECU looks for a drop in the
measured flow, if it doesn't see a drop, it turns on the light, because you
are making too much emissions, or have blocked off the egr.  Correspondingly
you can also get too much drop in flow, meaning there is too much
recirculation of exhaust gases.  Thing is, it is outside the specification
that the ECU is calling for, so the light comes on.  None of what has
transpired so far should cause stuff like this Rolf.  The ecu drives a pulse
width modulation solenoid, that regulates vacuum to the diaphragm that
controls the EGR valve. Maybe the egr valve needs cleaning, and is stuck in
open position, or the return spring has failed inside the dashpot that moves
the egr vlave.   Thing is , it is a feedback driven system, so something
physical has to quit working to effect a change like this.  I'd pop the egr
valve off and inspect it first, and go from there.
-j

> -----Original Message-----
> From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com]
> On Behalf Of Rolf Pechukas
> Sent: Sunday, May 09, 2010 1:55 PM
> To: vwdiesel at vwfans.com; VW-TDI at yahoogroups.com
> Subject: Re: [Vwdiesel] *CEL light on middle of road trip*
> 
> ok, so I had the code pulled at AutoZone
> CEL is on b/c "EGR excessive flow detected"
> 
> (reminder: 2001 Golf TDi, smelly exhaust, CEL, recent shop error
> alternator replacement forgot intake hard pipe, 30 mi driving w/ turbo
> disconnected)
> 
> now I don't understand these fancy TDi's at all
> but my simpler N/A mind sees 'excessive exhaust' and thinks 'burnt
> valves'
> 
> is this just a matter of faulty EGR valve? possibly caused by
> unfiltered intake air? driving 'hard' (shop suggestion to 'reset
> computer')?
> 
> any other thoughts on this result?
> 
> thanks for all the input,
> 
> Rolf in MA
> 
> 
> > You should have them pulled sooner than later; but I wouldn't allow
> it to ruin a drive.  Nor would I be unduly bothered by waiting a few
> days.  "Serious" faults will trigger an idiot light: oil, temp, ABS.
> OTOH, if the CEL is blinking, then it is serious, and you shouldn't
> drive it.  [At least that is what I think the manual said.]  Just find
> out what is causing it before the next inspection, and get it fixed
> between now and then.  There is a good chance that you can ignore it,
> once you find out what the code is, and have it repaired at your
> leisure.
> >
> > Shawn Upton, KB1CKT
> 
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