AIR REPAIR OBDII REVIEW 2008 7
determined by using propane enrichment tool “blipped” propane
while pattern was still lean, voltage rise from lean to rich in less
than 100 mS from 300 mV to 600 mV). If this were an IM240 failure
I would recommend replacing the Bank One sensor. That is exactly
what I did in this case and after doing so (not an easy task on this
baby), the Explorer set both of the O2 monitors after driving it only
two blocks from the shop. The Mode 6 numbers quickly evened out
as well, 787 for B2S1 verses 804 for B1S1.
I don’t know why the PCM didn’t flag the Bank One upstream
O2 sensor and turn on the MIL light. It obviously thought there was
a problem so it didn’t run the monitors.
The two lessons that I will remember from this experience are,
first, if the monitors won’t run, there is a problem in the OBDII sys-tem
and all of the fancy drive traces in the world probably won’t set
those monitors. The second lesson is that despite what I suspect
a lot of us learned in our OBDII training, the OBDII system will not
recognize every problem by illuminating the MIL light. If the moni-tors
will not set, after a reasonable amount of driving, even if there
are no codes, I am going to diagnose the vehicle as if it is an IM240
failure and start scoping the individual sensors with my DSO.
If anyone has any input on this issue, please feel free to con-tact
me, Scott Kendall, at (847) 394-3030.
Stubborn Monitors
Continued from page 6.
OBDII Readiness Case Study
From the April 2005 issue of Air Repair.
By Angelo Vitullo, Emissions Program Instructor,
Automotive Technology Department; St. Louis Community
College, Forest Park Campus
The owner of a 1998 Chrysler Cirrus, with a 2.5L engine and
A/T, SMPFI, and odometer at 91,000 miles informed a service
manager of an OBDII emissions test reject because of monitors.
The inspection reports showed the service manager that the
vehicle had been rejected at the test station seven times over a
five-month period. Setting monitors during normal driving wasn’t
an issue since a cross-country trip was taken during that five-month
period. The repair facility scan tools also confirmed the
test station monitor status report. Many unsuccessful things were
tried, including the installation of a remanufactured PCM, and the
technician driving the vehicle according to drive trace procedures
also accomplished nothing. Finally the vehicle was returned
with instructions to “drive the car for a few days.” The customer
departed more frustrated than ever.
Once I got involved at Outreach’s request, I contacted the
repair facility and the customer directly to get the information I
needed to repair the vehicle. Using my scan tool to check the
OBDII system, the only monitor that was complete was the HO2S
monitor. This monitor is enabled at idle after a cold start with
engine temperature
below 127 degrees F
and battery temperature
within +/-27 degrees
of engine temperature.
I wondered why that
monitor ran and no
others did?
When eyeballing long
lists of live sensor data, it is easy to overlook key pieces of
information while trying to rationalize every value displayed. But I
did notice the Ambient/Battery Temperature Sensor was sending
an erroneous very cold signal of -7.6 degrees F. On a 70 degree
F day, this was a red flag.
By researching the “enabling criteria” necessary to run
monitors for the EGR, HOS2 and CAT monitors, I found they all
require a minimum ambient temperature of 19 degrees F.
Also, the OBDII Misfire Counter was not functioning. This
vehicle, as with most others, must “learn” the specific electrical
characteristics of the crank sensor, the crank sensor air gap,
the machining characteristics of the crankshaft tone wheel,
and so on. Chrysler calls this learning process the Adaptive
Numerator. There is a drive cycle consisting of a series of
vehicle decelerations required to perform this learning process
for this particular vehicle. Some brands of vehicles can perform
this learn function in
the shop bay. Only
research will reveal
the proper procedure
for the subject vehicle
in your shop. Without
guidance, we are lost.
The scan tool readout
stated the vehicle did
not complete the Adaptive Learn procedure, hence the misfire
counter, a continuous component monitor (CCM) was disabled.
In researching the enabling criteria for the Misfire Monitor, I
learned it also would be disabled due to the ambient temperature
requirement of 19 degrees.
While researching the wiring diagrams and component
locations guide, I saw there was a temperature measurement
thermistor located behind the left headlamp housing. It was a
three- wire sensor called the Battery Temperature Sensor. The
calibration error had suspended the running of all monitors
except the HO2S Heater Monitor. Why? Because that monitor
will run as long as there is a cold start and battery temperature
is within +/- 27 degrees of engine temperature. In other words
if the engine coolant temperature is 18 degrees or less during
a cold start the HO2S Heater Monitor will run. Knowing a prior
repair shop replaced the PCM in vain, I double checked the part
number to confirm it was correct.
I was confident the problem was the Ambient/Battery
Temperature Sensor. After a wiring check I replaced the sensor
and, using the scan tool, recorded a realistic temperature
OBDII MON
DISABLED S TATUS
OBDII MON DISABLED LoTemp : YES
OBDII MON DISABLED LoBatt : NO
OBDII MON DISABLED LoBaro: NO
(Continued on next page)
SENSORS
CURRENT ADAP CELL ID : O
ENG COO LANT TEMP DEG : 73.4F
ENG COO LANT TEMP VOLT: 2.59V
IN TAKE AIR TEMP DEG : 68.0F
