On Sunday, September 20, 2015 at 7:58:13 PM UTC-4, wrote:

Actually it is not pending codes that are the issue. It is the
readiness monitors.. Can't remember how many readiness monitors there
are - but there's a catalyst monitor, a O2 sensor monitor, and EGR
monitors, and O2sensor heater and cat heater monitor on some vehicles.
These are the intermittent monitors that need to be "set" .

Setting the monitor just means they have been through one or more
test sequences and have aquired valid data..


I was thinking that too, ie that it's the monitors, not pending codes.
Pending codes would be fault conditions that have been detected but
haven't occurred enough to put activate the check engine light. The
emissions monitors are flags that are set on the critical emission
related systems. If you clear the computer, those flags get cleared.
When the car is driven, they get set again over time as the system
accumulates info that shows they are working. There are about 10,
I think. Most get set within minutes. The fuel evap system takes the
longest, probably takes multiple drive cycles to set.

Here in NJ with older cars you can pass inspection with two not
set. Newer cars, no more than one can be not set. Maybe some states
are concerned with actual pending codes, but I doubt it, because
they don't necessarily mean anything is wrong and would just create
a lot of drama for nothing.