February 2006 Air Repair OBDII Review 19
ALL Enabling Criteria Must Be Present to Run Monitors
From the July 2005 issue of Air Repair.
By Jeff Katz, Owner, Katz Automotive, Elgin
Many techs are seeing monitors that can be very difficult
to complete. With persistence and following enabling
criteria exactly, we’ve found that enough monitors can be
completed in order to take an OBDII emission test. Our
shop recently encountered a 3.0 liter 1996 Caravan with
some very stubborn monitors.
The van originally failed with a P0443 (evap purge
solenoid circuit). It was tested
and failed six months later with
the same code. We always
baseline any emission repair
before doing anything, and the
odd thing we noticed was that
the CAT monitor was incom-plete.
All other monitors were
completed and our code P0443
was in memory.
A P0443 code indicates a
problem in the purge solenoid
circuit. This vehicle does not
have a leak detection pump and
purge is monitored similar to an OBD-I vehicle. Evap is
not supported on this vehicle; it is monitored by the
Our problem was that a transmission linkage rod
rubbed through the wiring harness and power feed wire
to the evap purge solenoid. We repositioned the harness
and soldered the wire back together. We did have to
disconnect the battery because the wiring repair was
directly underneath it. This resets all monitor status and
clears codes. No matter what we did, we could not get
this van to complete enough monitors to take the test.
The supported non-continuous monitors on this vehicle
are the CAT, O2, O2 Heater, and EGR. The O2 Monitor
would set to complete as soon as the van was started,
leaving us needing one monitor to run to take the emission
We have a specific route that we drive to run moni-tors.
It usually takes about fifteen to twenty minutes and
includes both city and highway driving. We look up the
drive traces in the NCVECS CD or Alldata, set the
scanner to monitor status, and drive until we pass enough
monitors to take the test. Eleven test drives later nothing
else would complete. I got in touch with a Chrysler
representative who helped us out. His advice was to put
the van on a lift, run it up to highway speeds, and let it
coast all the way down to idle without touching the brake.
He said sometimes the monitors would run during this
long decel. We were a little apprehensive about doing it
because it had 150,000 miles on it and one of the issues
was a small cooling leak in the area of the water pump.
You guessed it, at about 55 mph the timing belt let go.
During the repair the tech noticed that the thermostat was
also stuck open.
I wondered why a van would run a monitor on the
lift but not the highway. This
van’s temperature gauge stayed
in the middle throughout the
test drive; but we never
actually checked engine
temperature during the test
drive. One of the enabling
criteria for the EGR monitor
was an engine temperature of
above 170 degrees F. So our
next test drive we set the scan
tool to data list and recorded it.
We only needed one monitor to
When we started the test drive we were at 178
degrees F; once on the road the engine quickly cooled off
to 136 degrees F, preventing the monitors from running.
Remember, we have to maintain 170 degrees F coolant
temperature. After a new thermostat, the engine main-tained
a steady 194 degrees F on the road. The odd thing
is that the CAT monitor completed on the first test drive.
The van passed the OBDII emission test without complet-ing
the EGR or O2 Heater monitors.
Ten days later the van returned for some additional
maintenance. We rechecked it, and all of the monitors
were completed with no new codes. The customer did
mention that the van heated up faster and the heater
Watching the enabling criteria closer would have
saved a lot of time. We don’t know why the O2 Heater
initially wouldn’t complete since that monitor was
supposed to run within ten minutes after the engine was
shutdown. We also don’t know why the O2 Monitor set
to complete without the O2 Sensor even getting hot. And
finally, why did the monitors seem to run out of order?
But engine temperature was a critical factor for this
vehicle to run enough monitors to pass the test.
Remember ALL enabling criteria must be present in
order to run the monitors.
Damage done by 1996 Caravan transmission linkage rod.
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