This is just a WAG (or something to discuss) based on fighting this thing for 3 years. I think the problem I'm seeing is a malfunction of the circuits or software that does this:
The term “Trip” has different meanings depending
on what the circumstances are. If the MIL (Malfunction
Indicator Lamp) is OFF, a Trip is defined as
when the Oxygen Sensor Monitor and the Catalyst
Monitor have been completed in the same drive cycle.
When any Emission DTC is set, the MIL on the
dash is turned ON. When the MIL is ON, it takes 3
good trips to turn the MIL OFF. In this case, it
depends on what type of DTC is set to know what a
For the Fuel Monitor or Mis-Fire Monitor (continuous
monitor), the vehicle must be operated in the
“Similar Condition Window” for a specified amount of
time to be considered a Good Trip.
If a Non-Contiuous OBDII Monitor, such as:
² Oxygen Sensor
² Catalyst Monitor
² Purge Flow Monitor
² Leak Detection Pump Monitor (if equipped)
² EGR Monitor (if equipped)
² Oxygen Sensor Heater Monitor
fails twice in a row and turns ON the MIL, re-running
that monitor which previously failed, on the
next start-up and passing the monitor is considered
to be a Good Trip.
If any other Emission DTC is set (not an OBDII
Monitor), a Good Trip is considered to be when the
Oxygen Sensor Monitor and Catalyst Monitor have
been completed; or 2 Minutes of engine run time if
the Oxygen Sensor Monitor or Catalyst Monitor have
been stopped from running.
It can take up to 2 Failures in a row to turn on the
MIL. After the MIL is ON, it takes 3 Good Trips to
turn the MIL OFF. After the MIL is OFF, the PCM
will self-erase the DTC after 40 Warm-up cycles. A
Warm-up cycle is counted when the ECT (Engine
Coolant Temperature Sensor) has crossed 160°F and
has risen by at least 40°F since the engine has been
This problem never occurs when the Catalyst monitor is not complete. Also it never has pending or active codes prior to or after failure.