Oxygen sensor performance.pdf

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May & June 2012
Oxygen Sensor
Performance
Oxygen
sensors have
been used in
automobiles
for over 30
years but are
often taken for
granted as part of the engine controls
system. They have progressed from
single wire non-heated oxygen sensors
to heated oxygen sensors and, in some
vehicles, wide band oxygen sensors.
Proper oxygen sensor operation
is critical for vehicle emissions, fuel
economy and engine performance.
However, technicians may misdiagnose
the performance of an oxygen sensor
if they are not familiar with how one
works or are just reading a Diagnostic
Trouble Code (DTC) from a scan tool
without properly diagnosing the engine
control system. Here’s a closer look at
what an oxygen sensor does and how it
works.
The switching Oxygen Sensor (O2S)
is unique among the engine control
system sensors because, when hot, it
acts like a battery and is able to generate
its own low voltage signal that is sent
to the Engine Control Module (ECM) to
monitor the amount of oxygen in the
exhaust. The O2S provides feedback to
the ECM, which uses the information to
manage fuel delivery and maintain the
stoichiometric air-fuel ratio of 14.7:1 (for
gasoline engines).
The electrically heated oxygen sensor
(HO2S) is used to reduce the amount
of time it takes for the sensing element
to become hot and active, allowing the
fuel control system to go into closed
loop more quickly, which helps reduce
emissions. On some vehicles, it is also
used to help keep the engine control
system in closed loop when the engine
is at idle and may have a low exhaust
flow rate. On newer vehicles, the ECM
determines the heater temperature by
measuring the current flow through
the heater and calculating the heater
resistance, which correlates to sens-
ing the element temperature, and then
the control module can predict sensor
element temperature based on heater
resistance.
IN THIS ISSUE
Oxygen Sensor Performance . . . . . . . . . . .1
ACDelco Battery Warranty Changes . . . .2
Updated Wheel Alignment
Specifications . . . . . . . . . . . . . . . . . . . . . . . .2
ACDelco Online Specialty Catalogs . . . . .4
Competitive Parts Analysis
Helps Ensure ACDelco Quality . . . . . . . . . .5
The GM Supplier Discount Pays Off . . . . .6
Potential History DTCs after
Servicing a Vehicle. . . . . . . . . . . . . . . . . . . .6
Take the TechConnect Reader Survey . . .6
Tech Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Training Update. . . . . . . . . . . . . . . . . . . . . . .8
Measuring Oxygen
The switching O2S has a center
element made of ceramic material,
zirconia, and two platinum electrodes
that make up the inner and outer
surfaces of the center element. The
inner surface of the sensor — exposed
to outside air through its wire out to
the harness connector — forms the
positive terminal of the O2S circuit. The
platinum coating on the outer surface of
continued on page 3
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e-EDITION
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www.acdelcotechconnect.com,
click
the TechConnect Magazine link
ACDelco Battery
Warranty Changes
ACDelco is transitioning away from a pro-rated battery replacement warranty to
a new, simpler, free replacement strategy for ACDelco batteries to help reduce
customer confusion and dissatisfaction.
Here’s how it works: On a 30-month free replacement battery, for example, if
the battery is up to 30 months old, it’s replaced for free. If it’s 31 months old, a
new battery is sold to the customer. It’s that simple.
The new free replacement warranty batteries will have new part numbers,
which began being rolled into inventories in March. Batteries purchased under the
previous part numbers and warranty will still be warranted on the pro-rata basis.
The warranty is what the battery has on it. Here’s a quick look at the batteries
and their new part numbers:
• Professional 24-5YR (18-month free replacement warranty) – part number
24P (Professional)
• Professional 24-6YR (30-month free replacement warranty) – part number
24PS (Professional Silver)
• Professional 24-7YR (42-month free replacement warranty) – part number
24PG (Professional Gold)
The previous 60 Series battery is transitioning to the Advantage brand and
will also carry a free replacement warranty; in the example above, it will be part
number 24A and have an 18-month free replacement warranty.
In addition, non-automotive batteries have been moved to a simplified and
improved free replacement warranty.
New point-of-sale materials have been developed to support these changes.
For more information, contact your local ACDelco representative.
– Thanks to Dan Carter
Volume 19, Number 3 (TS-PU-0007-12)
ACDelco TechConnect is published bi-monthly
and online for technicians of Total Service
Support (TSS) and Key Fleet accounts to
provide timely service information, increase
knowledge and improve the performance of the
service center.
ACDelco 360 represents our mission to look
at our businesses at every possible angle to
provide value and assistance to our distributors
and their customers as well as offer a full circle
of support with programs, tools, training and
marketing focused on enhancing and growing
our partnership successfully.
Publisher:
Rick Balabon
ACDelco
E-mail
/
richard.balabon@gm.com
Editor:
Greg St. Aubin
ACDelco
E-mail
/
gregory.staubin@gm.com
Technical Editor:
Mark Spencer
E-mail
/
mspencer@gpworldwide.com
Production Manager:
Marie Meredith
Desktop Publishing:
5by5 Design LLC
E-mail
/
dkelly@5by5dzign.com
Write to:
*
ACDelco TechConnect
P.O. Box 500
Troy, MI 48007-0500
On the Web::
To read and search recent issues of
TechConnect
online:
– www.acdelcotechconnect.com,
click the
TechConnect
Magazine
link, or
– Log in to the ACDelco LMS, click
the Resources link
ACDelco service tips are intended for use by professional
technicians, not a “do-it-yourselfer.” They are written to
inform those technicians of conditions that may occur on
some vehicles, or to provide information that could assist
in the proper service of a vehicle. Properly trained techni-
cians have the equipment, tools, safety instructions and
know-how to do a job properly and safely. If a condition
is described, it cannot be assumed that the information
applies to all vehicles or that all vehicles will have that
condition.
All materials and programs described in this magazine
are subject to change. Submission of materials implies
the right to edit and publish. Inclusion in the publication
is not necessarily an endorsement of the individual or
the company.
TechConnect
is published for ACDelco by Sandy
Corporation, Troy, MI.
Updated Wheel Alignment
Specifications
Before performing a steering wheel
angle/front toe set or wheel alignment
check/adjustment, be sure to verify the
wheel alignment specifications for the
vehicle in order to avoid any complica-
tions from using the incorrect wheel
alignment specs. This can occur if the
wheel alignment rack specifications
are not updated regularly. In addition,
the vast variation in specifications,
depending on the type of vehicle and
tire, suspension and engine options,
make it easier to use the wrong wheel
alignment specs.
The only recommended source of
current, accurate wheel alignment
specifications (both targets and toler-
ances) is the Service Information for
the particular vehicle make/model.
The specifications indicated on the
wheel alignment rack should always
be verified with the appropriate Service
Information.
In the first quarter of 2012,
the following GM models had
updated/changed wheel alignment
specifications:
• 2007-2012 Acadia
• 2007-2012 Enclave
• 2009-2012 Traverse
• 2010-2012 Corvette
• 2010-2012 LaCrosse
• 2011-2012 Regal
Check the alignment specifications for
these models in the appropriate Service
Information against the alignment
machine specifications before perform-
ing an alignment. Be sure to take into
account all related option content on
the vehicle, including optional tire and
suspension packages. These updated
specifications most likely will not be
included in the latest specifications from
alignment machine manufacturers.
– Thanks to David MacGillis
2
©2012 ACDelco. All rights reserved.
Oxygen Sensor Performance –
the sensor element — exposed to the
exhaust gases — forms the negative
terminal of the sensor circuit.
This oxygen-sensing cell becomes a
galvanic device (battery) when heated,
(the exhaust gases keep the sensor at
about 600° F/315.5° C) and it generates
an electrical signal as the result of the
interaction of outside air, the inner sur-
face of the element, the exhaust gases,
and the outer surface of the element.
The amount of voltage the O2S gener-
ates is proportional to the difference
between the amount of oxygen in the
outside air and the amount of oxygen in
the exhaust gases.
continued from page 1
because it indicates a hot engine. The
coolant gauge is only an indicator of the
condition. The engine is overheating,
not the gauge
The exhaust from a rich air-fuel ratio
will contain almost no oxygen. With a
large difference between the amounts
of oxygen contacting the two sur-
faces of the sensor, the sensor is
able to generate more voltage. When
the exhaust gas indicates it is rich,
the voltage output is high (above 450
millivolts) and the ECM will try to lean
the mixture out.
Lean:
The exhaust from a lean air-fuel ratio
has about 2% oxygen. With a smaller
difference between the amounts of
oxygen contacting the two surfaces
of the sensor, the sensor generates
less voltage. When the exhaust gas is
lean, the sensor’s voltage output is low
(below 450 millivolts) and the ECM will
try to enrich the mixture.
This is where having a good
understanding of engine controls and
oxygen sensor operation is particularly
important. For example, when a mis-
fire occurs, incomplete combustion
leaves an abundance of oxygen in the
exhaust, which passes the O2S and is
interpreted by the ECM as a lean (lots
of oxygen vs. fuel) condition. The ECM
responds by increasing the fuel deliv-
ery. This condition is very hazardous to
the catalytic converter.
OEM Sensors
If proper diagnosis leads to replacing
a malfunctioning oxygen sensor, what
are you going to replace it with? There
are instances of aftermarket oxygen
sensors that may fit but have question-
able functionality; the sensor tip open-
ings may have different configurations
or the length of the sensor body may
cause interference issues. ACDelco has
learned of one aftermarket supplier that
has consolidated several GM/ACDelco
O2S part numbers and applications into
a single aftermarket part number.
Using the Data
The ECM typically applies a reference
voltage, also known as bias voltage, to
the sensor of 450 millivolts (some new
ECMs use 1.9 volts as its bias voltage).
The ECM uses this reference voltage
with the voltage generated by the O2S.
A normal oxygen sensor reading varies
above and below the bias voltage; in
a normally operating engine, the pre-
catalyst O2S output voltage fluctuates
rapidly between 100 millivolts and 900
millivolts. This rapidly changing volt-
age reflects the changes in the air-fuel
ratio. The ECM adjusts injector pulse
width in response to the changing
O2S signals to try to keep the correct
air-fuel ratio. This data also is used by
the ECM to determine short-term and
long-term fuel trim. Here are a couple
of examples:
ACDelco O2 sensor tips monitor oxygen
content while shielding the sensor from
thermal shock.
Catalyst Efficiency
GM engineers spend a lot of time
designing the OEM sensors to work
properly, in both fit and function. In
OEM and ACDelco sensors, the open-
ings in the tip are specifically designed
to monitor the oxygen content and the
tips are designed to shield the sensor
from thermal shock, which is caused
by condensation in the exhaust system
hitting a hot sensor. Plus, the wire lead
lengths are designed to fit (not be too
short and possibly pull wires out of the
connector or too long and rub against a
chassis component or melt against the
exhaust system), and the O2 electrical
heater resistance tolerances are set to
properly maintain the correct tempera-
ture of the internal sensing element, all
ensuring proper operation and perfor-
mance.
Finally, be sure to follow the appropri-
ate Service Information when replacing
an O2 sensor or making repairs to the
wire lead as there are specific repair
instructions and torque specifications
for this procedure.
– Thanks to Rick Balabon
In addition to fuel control, the ECM
uses O2S information to perform
diagnostics and monitor catalyst
efficiency. A post-cat O2S will not
Rich:
vary the voltage reading as quickly
The Earth’s atmosphere contains
as a pre-cat O2 sensor if the catalytic
about 78% nitrogen and 21% oxygen.
convertor is operating properly. A leak
in the exhaust system
can lead to misdiagnosis
of the pre- or post-cat
O2 sensor if proper diag-
nosis is not followed.
Anything that will allow
extra oxygen into the
exhaust stream can
change the amount of
oxygen the O2S mea-
sures and may set a
DTC. Just because an
O2S DTC is set does
not mean it is caused
by a bad sensor; it may
just be that the sensor
is seeing information
outside of the expected
range. This would be
similar to blaming the
The ECM uses the bias voltage and the O2S voltage
engine coolant gauge
to adjust the air-fuel ratio.
3
ACDelco Online Specialty Catalogs
WISE Internet Parts (WIP) is an online parts catalog
and ordering system that connects you to your ACDelco
distributor’s inventory, pricing and parts information 24 hours
a day, seven days a week. In addition to the regular ACDelco
parts catalog, WIP offers several specialty catalogs.
New 2nd quarter catalog enhancements include:
• Search by the last 8 digits of a VIN for easier look up
• Show/hide price so service center owners can remove
their cost from the screen
Illustrated Catalog
ACDelco’s Illustrated Catalog provides a unique view and
navigation style that makes it easy to find and order the parts
you need. The online catalog features GM vehicle applications
with aftermarket categories and sub-categories.
A/C Catalog
The unique, horizontally-aligned online ACDelco Air
Conditioning Catalog emulates the style of many paper cata-
logs. After identifying a vehicle, all the A/C parts are listed
horizontally across the page, making it quick and easy to view
all the A/C parts needed for a vehicle in one efficient catalog
search.
The easy-to-use navigation of the GM vehicle application
catalog enables technicians and parts department personnel
to instantly find the desired parts. It's as easy as 1, 2, 3.
1. Click the part groups
2. Explode the view to navigate from part group down to
the specific parts needed, without having to know or
guess the correct categories
3. Order the part
Catalog features include:
• VIN filtering, application and ystem illustrations all on the
s
SAME page.
• Aftermarket-friendly categories and sub-categories
– Notepad tool to view and compare application notes
• Exploded view of GM system llustrations with part
i
number identification
– Zoom controls for accurate part identification
– Color coded to identify ACDelco parts
– Fast moving parts identified with a flame icon
• Vehicle search options
– Year, Make, Model
– Complete VIN filtering using vehicle options and build
• Part search options
– Category/Sub-category
– Part name/Part number
– Key word
• Parts detail
– Imaging
– Supplier Part availability
– Ordering capability
4
Catalog enhancements include:
• A new layout to optimize the orizontal alignment
h
• Rear parts (where applicable)
• An order summary added to the main page
• Multi-view images and product information on a "smart"
page that links from the part number
• Labor references
In addition to the A/C catalog on WIP, a stand-alone A/C
catalog is available on acdelcotechconnect.com.
Chemical Catalog
The specialty ACDelco Chemical Catalog allows users to
search by the GM and/or ACDelco part number as well as
chemical type. In order to make it easier to find what you’re
looking for, the catalog details 20 chemical types, such as air
conditioning, power steering fluids, brake fluids and motor oil.
continued on page 5
Competitive Parts Analysis Helps Ensure
ACDelco Quality
ACDelco routinely performs testing and analysis of
products with competitive parts to ensure that the high-
est quality products are delivered to ACDelco customers.
Recently, an analysis of an ACDelco fuel pump and a compet-
itor’s fuel pump for 2002-2003 GM full-size trucks and SUVs
showed some striking differences that can impact durability
and performance.
ACDelco electric fuel pumps are designed to provide
outstanding fuel delivery, quick engine starts, long-lasting
durability, and proper fit. Quality testing and tear-downs are
part of ACDelco’s commitment to continuous improvement.
When comparing the fuel pumps, here are some of the
built-in quality features that were evident on the ACDelco
pump.
The ACDelco pump has 10 motor contact points, while the
competitor’s pump has 8 contact points. More contact points
makes the spinning of the fuel pump turbine more efficient
and quieter.
The fuel sender of the ACDelco pump has internal springs
in the reservoir, which eliminates the potential for pinching
wires or rubbing through the fuel line. The competitive fuel
pump has external springs on the guide rods.
In addition, the ACDelco fuel sender has thicker, more
robust fuel level sensor wiper contacts and wear pads for
enhanced durability.
ACDelco’s wear pads are designed for long-lasting durability.
The ACDelco fuel pump also features a jet pump to pre-
vent fuel pump starvation when the fuel level is low. The
competitor’s pump doesn’t have a jet pump.
Finally, ACDelco uses 100% new parts, and the quality
testing of those parts is evident when tearing down these
fuel pumps. The wear marks on the armature of the motor,
for example, indicates the end-of-the-line quality testing all
ACDelco fuel pumps go through to ensure full functionality
More contact points provide more efficient turbine operation.
The ACDelco fuel pump also has a shorter fuel reservoir,
reducing the chance to pinch the fuel lines.
Wear marks indicate the quality testing performed
on ACDelco pumps.
The ACDelco fuel pump, left, has internal springs in the reservoir,
unlike the competitor’s external springs on the guide rods.
and proper performance. The competitive pump is clean with
no marks, showing it has not completed the same extent of
full-functionality testing as the ACDelco part.
– Thanks to Dan Carter
• 40 Chevrolet and GMC medium-duty models
• Over 1,800 part numbers
• Over 280,000 applications
• Virtually all ACDelco product lines
For more information about WIP and the ACDelco
specialty catalogs, go to acdelcotechconnect.com and click
the eBusiness tab.
– Thanks to Kelli Abbott
The motor oil category offers a search by weight or by type:
conventional/mineral, synthetic blends, or full synthetics.
In addition to chemical type, specification information by
application is offered with the ability to link to the desired
product from the specification area.
In addition to the WIP chemical catalog, there also is a
stand-alone chemical catalog on acdelcotechconnect.com.
GM Medium-Duty Applications
GM medium-duty applications will be released in all catalogs
in June and will include:
5

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