Codes Stored with no CEL?

[Brett Dikeman]

On Wed, Jul 22, 2009 at 1:37 PM, Dan DiBiase<d_dibiase at yahoo.com> wrote:

> Will the on-board computer store any codes that may be generated even though there is no
> , nor has there been, any Check Engine
> Light flashing or warnings?

I've slowly been learning about more modern (hah) engine management
with my new Volvo, which appears be Motronic ME7-ish based.  I think
the S4tt is 7.1; dunno about the newer A4, but I'd suspect the 1.8 is
similar.  The 2.0 probably uses a new generation.

One thing that seems consistent since the first Motronic Audis like
the 200q20v: they store intermittent fault codes that don't trigger
the CEL (and for example, in the case of the 3B, you will not get that
intermittent code if you do a blink retrieval.)

  It is very common for there to be several different misfire counters
(which are also per-cylinder), and unless you drive the car in such a
way that it repeatedly triggers the misfire, it might not actually
store a major fault code and pop on the CEL.  The counters are still
there, though, and when one cylinder has a bunch of misfires and the
others don't, boom, you know where to look.  If it's just one
cylinder, a failing coilpack is certainly a strong suspect.

  On the Volvo, the CEM also stores counts...so, for example, when I
had my car PPI'd, they found an "interior air quality sensor" code,
but it had happened once out of hundreds of power cycles.  No sweat.
Reset, never came back. Same with some suspension errors, like sensor
values being out of range.  The count was 1, so the shop suspected it
happened from when they put the car on a lift and turned the ignition
on.

It would definitely be worthwhile to try and connect with someone who
has VAG-COM.

Brett