On May 15, 3:09*am, wrote:
> Dear Experts,
>
> I've had some more adventures with my 99 Lexus ES300.
> Now, about 107K miles.
>
> I had the alternator changed in the winter.
>
> Some weeks later, I was driving cross country.
> I got a check engine light.
>
> I checked the code. *It was the P0420,
> Catalyst System Efficiency Below Threshold (Bank 1)
>
> I pulled out my OBD tool, and erased it.
> But It came back again a few times.
> Sometimes, it took only about 40 miles.
> Another time, it took 200 miles.
> I probably got the code, and erased it at least 4 times.
>
> It only happened when I was driving cross country, all day long.
> Since I returned to the city, I have not got the code.
>
> Today, I went to go get a smog check in California.
>
> Before I left, I connected the OBD to my laptop, and erasad all codes,
> just to be sure.
>
> When I went for the smog test, everything was fine, except I failed:
>
> Vehicle failed the MIL/Check Engine Light due to failure to
> successfully complete all OBD self tests.
>
> I've since been reading more about the OBD hehttp://www.smogtips.com/functional_inspection.cfm
>
> One possibility I read the
>
> Step D. Drive your vehicle for one week under normal driving
> conditions. During this period the emissions computer is gathering
> data and re-learning your vehicle's emissions components and systems.
> The emissions computer OBDII (on-board diagnostics) system must
> complete at least one drive cycle (in some cases two or three). A
> drive cycle is a sequence of internal tests which the emissions
> computer runs while your vehicle is being driven. This insures all
> emissions systems are functioning properly. Proper "readiness flags"
> are set as the computer completes it's cycles. Test cycles are unique
> to a vehicle. Certain cycles run under very strict parameters, and may
> require extended driving time to trigger on. Cycle data and readiness
> flag information is available through your dealership's service
> department. The data vary widely.
>
> My questions.
>
> 1) * Does Step D make sense, given that I'd erased the codes? * If I
> do drive the car for a few days like this, should I be able to pass
> the test?
>
> 2) *If I erased all the codes, are they really all erased? *Or, is
> there still some log about them? *That they were there, I erased them,
> and they are just flagged inactive now?
>
> Thanks a lot!

Your mistake was erasing the codes immediately before going for the
test. Several parameters are not set to ready until a "drive cycle" is
completed. Next time, if the check engine light is not on, leave well
enough alone. If you complete the cycle and the check light does not
come back on, it should pass.

As far as number 2, if you successfully reset the computer, then yes,
the codes are gone. If there is a problem the code will be right back
in there though. Before you go back for a retest, read the codes but
none show up, do not reset.