12 Air Repair OBDII Review Volume 3 Number 1
On a hunch I highlighted and compared the data for
the two upstream O2 sensors. The numeric value for the
Bank Two sensor was lower than the one for the Bank One
sensor: 1024 for Bank One sensor one verses 787 for Bank
Two, sensor one. This was important because the Bank
Two sensor was new and the Bank One sensor was original
to the vehicle.
So at this point I had a perfectly running sport utility
vehicle with no codes or pending codes. All of the data
viewed through my scanner appeared normal except the
differential in the Mode 6 numbers for the two upstream
O2 sensors, but the PCM gave both of them a Pass. I had
to fix this thing after shooting my mouth off on the phone
to the Explorer’s owner. With the confidence of Ralph
Kramden on the old Honeymooner’s TV show, I had told
him, “I can fix any emissions failure sir, bring it in”.
I made some calls to some of the contacts I have found
in the industry and none of them had seen this problem
themselves. This is not surprising because if you think
about it, the Explorer was actually fixed from the perspec-tive
that the MIL light, which had illuminated because of
a bad O2 sensor, was now off and there were no Codes in
memory. Were it not for the retesting issue, no Tech would
consider the Explorer to have a problem. The monitors
needing to be set have only been an issue in Illinois since
January 2, 2004, so it is unlikely that any Tech would have
any significant experience at setting them.
It was time to break out my DSO and further test the
only suspicious sensor I could find, the other upstream O2
sensor. The only reasonable way to do this on the Explorer
is at the PCM, which is located at the center of the firewall.
Continued from page 11.
It was obvious on my scope that the Bank One sensor was
slow and lazy (as 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 recom-mend
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 experi-ence
are, first, if the monitors won’t run, there is a problem
in the OBDII system 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 contact me, Scott Kendall, at (847) 394-3030.
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.
Continued on page 13.
The repair facility scan tools also confirmed the test sta-tion
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
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
Click tabs to swap between content that is broken into logical sections.