I/M Readiness Code
The readiness function is implemented based on the J1979 format. A battery disconnection or clearing codes
using a scan tool results in the various I/M readiness bits being set to a “not-ready” condition. As each noncontinuous
monitor completes a full diagnostic check, the I/M readiness bit associated with that monitor is set to a
“ready” condition. This may take one or two driving cycles based on whether malfunctions are detected or not.
The readiness bits for comprehensive component monitoring, misfire and fuel system monitoring are considered
complete once all the non-continuous monitors have been evaluated. Because the evaporative system monitor
requires ambient conditions between 40 and 100
oF and BARO > 22.5 " Hg (< 8,000 ft.) to run, special logic can
“bypass” the running the evap monitor for purposes of clearing the evap system I/M readiness bit due to the
continued presence of these extreme conditions.
Evap bypass logic for 1997, 1998 vehicles:
If the evaporative system monitor cannot complete because ambient temperature conditions were encountered
outside the 40 to 100
oF and BARO range at speeds above 40 mph during a driving cycle in which all continuous
and non-continuous monitors were evaluated, the evaporative system monitor is then considered complete due
to the continued presence of extreme conditions. If the above conditions are repeated during a second driving
cycle, the I/M readiness bit for the evaporative system is set to a “ready” condition. (Note: Some 1997 and 1998
vehicles do not require catalyst monitor completion to bypass.)