Codes 12 and 21

My '97 Voyager 3.3L V6 is showing codes 12 and 21.

It recently went through a CA smog test and the HC levels were high --
almost at the failure point, so it is not unreasonable to think that there
is a problem with the oxygen sensor or associated wiring, but the code 12
seems odd.

I have not disconnected the battery, is there some other event that could
trigger code 12?

 

I'm assuming you can still use the key on-off-on-off-on to get codes
on your vehicle, and that that's how you're reading them.

12 is "start of codes", and meaningless beyond that when another code
appears (this isn't something I've ever seen documented, (1) but
people who know a lot more about what they're talking about than I do
tell me this, and (2) I've never seen another fault code without
seeing 12 as well). So I wouldn't worry about it.

 

I see it too. It just might be the starting code. For example, I always
see 12 and 55 for my start and finish, regardless if there are any
error codes or not. A bad oxygen sensor would give a rich mixture which
would show high HC levels, yes? As I understand it, the car is stuck in
rich mixture mode and cannot go into lean mode or "closed loop."

Since I am sitting here with the shop manual for company, on a Saturday
night, how pathetic, anyway, it says Diagnostic Trouble Code 12: Note:
This is not a code. It exists to provide reference information only.

I think this is bad technical speak for an arbitrary start to flashing
the codes at you. Not meaning to be a smarty pants, I guess 0 is hard
to show and would be ambiguous

 

Which shop manual? Real live FSM or cheap loser (Haynes, Chiltons)?
Year, vehicle?

 

I really can't use the ersatz manuals. Chiltons has always been too
obscure, as though a crib sheet for a mechanic. However, they do have
cheap CD's. Haynes is not too bad, but you can't have one tiny book
represent 10 years of different models with just one taken apart for
illustration. But sometimes it helps.

Nope, this was a genuine yellow factory shop manual from Chrysler that
I waited for and finally got on eBay at a price that was very good,
around $25 with shipping. Someone had suggested that that was possible
on this newsgroup, and that person was right.

In the future, I might be tempted to get the shop manual on paper and
on CD if I had to search for things. As it is, the index is good enough
but the CD might be nice for printing out pages to get dirty as needs
be. The cost my for car for paper and CD would be, with shipping now,
new, well over $160. And I noticed that the shop manuals are getting
more expensive with the newer cars. Maybe they are also getting a wee
bit more clear, I seem to notice. So that's a good trend.

My vehicle is not the same as the poster, but close enough, a 1994 3.0
Liter Mitsubishi. Since I am rambling on here, I might want to correct
something. I am not sure if I got 12 and 55 without any error codes. I
don't remember if only the 55 flashed when there were not any error
codes. Hold on, have to do a Boolean search in my notes ... nope, don't
know. Seems I get the 55 if no errors and a 12 and 55 if an error with
my particular vehicle. But in any case, the manual does say the 12 is
not an error code but sort of an index point if you will, a header, to
point that error codes are coming.

Say, I noticed on your web site you like binary. I'll bet you can do
assembly code then? Always wanted to know how to divide by 4 in
assemble so I could get 4 Hz bins in the FFTs.

 

I've got FSMs for a couple of vehicles in the right year range (1987
Chrysler FWD, 1995 Neon, 2000 LH is too late since 10101 with the key
doesn't work for it) and none actually document that 12 is Start of
Codes (though, like I said, people who know more than I do tell me
that's the case, and I've never found any evidence they're wrong).
Good to hear about a manual that agrees!

The details depend on the specific architecture -- but assuming you're
dealing with integer data (which you'd better be, if you're doing an
FFT), you can always divide a power of two by right-shifting by the
power. Since 4 is two squared, you can do a right-shift by two bits.
This is wandering off-topic, so if you've got questions send me an
email.