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Generator Operation and Troubleshooting 1
May 2002
Volume 4, No. 5
A monthly publication for GM Dealership Service Professionals
Service and Parts Operations
Contents
Generator Operation and Troubleshooting . . . . . .1
Which Password Should I Use? . . . . . . . . . . . .1
Tech Tips
Tracker Cruise Control Characteristics . . . . .2
Launch Shudder . . . . . . . . . . . . . . . . . . . .2
No TCC Command . . . . . . . . . . . . . . . . . .3
Headlamp Washer Relay . . . . . . . . . . . . . .5
HVAC AUTO Indicator Lamp . . . . . . . . . . . .6
Exterior Light Lens Guidelines . . . . . . . . . . .7
Class 2 Corner . . . . . . . . . . . . . . . . . . . . . . .2
Engine Oil Capacity Chart . . . . . . . . . . . . . . . .4
New A/C Testers Now Available . . . . . . . . . . . .5
Wiring Schematic Books Now Available . . . . . . .6
TAC Tips
Squeak/Rattle in Pillar . . . . . . . . . . . . . . . .7
Rattle in Roof Area . . . . . . . . . . . . . . . . . .7
Metallic Spring Rattle Noise . . . . . . . . . . . .7
Workhorse Custom Chassis . . . . . . . . . . . .7
A/C Squeak or Moan . . . . . . . . . . . . . . . . .7
Liftgate/Glass Wont Lock . . . . . . . . . . . . .7
CHMSL Loose or Fallen . . . . . . . . . . . . . . .7
Bulletins . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Techline News
site also contains links to SI 2000, TIS
2000, Techline Information, TechLink On-
Line, and Vehicle Calibration Information.
You will need an ID and password to
access any of these (other than TechLink).
The ID and password can be obtained
from your Area Service Manager. Or you
can call the Techline Customer Service
Center (TCSC) at 800.828.6860.
Thanks to Matt Singer
Which Password Should I Use?
Since we ran the introductory article
about the Service Information Forums
(technician chat room) in the March
issue, weve had numerous inquiries about
which ID and password to use.
TIP:
You cannot access the Service
Information website using your GM Dealer
World or GM Common Training passwords.
TIP:
This service is for the U.S. only.
To access the Forums, you must first go
to the http://service.gm.com website. This
Generator Operation and Troubleshooting
Over the past few model years, GM has
improved generator reliability by installing
larger generator bearings, higher temperature
greases, and high temperature press-fit diodes
across all generator lines. However, while
these design changes have improved
generator warranty over-all, the percentage of
good generator replacements has increased. A
recently completed analysis of generators that
were replaced shows that roughly half were
functioning properly. This raises concerns with
proper on-vehicle generator diagnosis.
Generator Operation
The generator's purpose is to provide
electrical power and maintain the battery
voltage at the proper level. When electrical
loads are switched on, the generator senses
this change and increases its output current
(amperage) to maintain the proper voltage,
until maximum generator output is reached.
Electrical loads in excess of generator
capability will cause the system voltage to
drop below normal. Example: a generator is
heavily loaded (summer city traffic) and is
attempting to recharge a discharged battery.
Generator maximum output increases
with engine speed, and typically at low idle
speed the generator output capability can be
exceeded.
Troubleshooting
When measuring generator output
amperage, make sure you are measuring DC
amps in the cable attached to the generator
B+ stud and that the current probe is fully
closed. Do not measure generator current at
the battery. Also make sure your voltage
measurement is correct and that the meter is
operating properly.
Q: What battery voltage level is proper, or
normal?
A:
The generator senses underhood
temperature and adjusts the voltage level
for proper battery charging. A warm
battery will accept a charge more readily,
continued on page 3 2
GM TechLink is a monthly magazine for
all GM retail technicians and service
consultants providing timely information
to help increase knowledge about GM
products and improve the performance
of the service department. This
magazine is a companion to the GM
Edge publication.
Publisher & Editor:
Mark Stesney
GM Service Operations
Mark.Stesney@GM.com
Technical Editor:
Jim Horner
Jim.Horner@SandyCorp.com
1-248-816-3641
Production Manager:
Marie Meredith
Desktop Publishing:
Greg Szpaichler, MediaWurks
spake@mediawurks.com
FAX number:
1-248-649-5465
Write to:
TechLink
PO Box 500
Troy, MI 48007-0500
GM TechLink on the Web:
http://service.gm.com
General Motors 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 technicians have the equipment,
tools, safety instructions and know-how
to do a job properly and safely. If a
condition is described, do not assume
that the bulletin applies to your vehicle
or that your vehicle will have that
condition. See a General Motors dealer
servicing your brand of General Motors
vehicle for information on whether your
vehicle may benefit from the information.
Inclusion in this publication is not
necessarily an endorsement of the
individual or the company.
Copyright© 2002 General Motors Corporation
All rights reserved.
No-Start or No-Start/No-Crank complaints
can occur for multiple reasons. However, one
of the reasons can be a shorted Class 2 bus.
Vehicle Theft Deterrent systems utilize the
Class 2 bus to communicate security
information between various controllers. For
instance, the BCM will get information from
the Passlock module and then communicate
with the PCM to allow or disallow fuel
delivery and/or starter enable.
When the Class 2 bus is shorted to either
ground or battery voltage, the controllers are
unable to communicate with each other. This
is because the voltage on the line is held
static at either ground or B+. The Class 2
message toggles the voltage on the bus
between 0 and 7 volts, but when the bus is
shorted, the toggling cannot take place.
Because the voltage remains static at either
ground or B+, the Class 2 message can't be
sent or received.
Without these Class 2 messages being
sent and received, the PCM won't get the
proper security messages which would
normally enable fuel and/or starter enable
and the customer will have a No-Start or No-
Start/No-Crank complaint.
TIP:
If the problem is intermittent,
remember to search for the U1300 - Class 2
Data Link Low, and U1301 - Class 2 Data Link
High--in "History". This will help determine the
source of the problem.
Thanks to Mark Harris
Tracker Cruise
Control Characteristics
On 1999-2002 Chevrolet Trackers, these
operating characteristics are considered
normal.
The first two conditions are related to built-
in time delays. If the customer attempts an
input during the time delay, the cruise control
module will ignore it. When the customer tries
a second time, the time delay is past, and the
input takes. The customer may comment
that it takes two inputs to get the system to
respond.
1. There is a 1 second delay between the
time the cruise control is turned on and the
time it will accept a set speed input.
Instruct the customer to wait at least 1
second.
2. There is a time delay from the moment a
brake or cancel input is received by the
module until the module will accept a new
set speed input. This delay increases with
vehicle speed, and at highway speeds may
be up to 3 seconds. Instruct the customer
to wait at least 3 seconds.
3. When braking or canceling cruise
operation, the cruise control module
immediately releases the throttle cable,
allowing it to snap back to the closed
position. If the operators foot is not in
position to catch the pedal, it will hit its
stop with a thump. This is normal and does
not require repairs.
4. Most GM cruise control systems will retain
a previously set speed in memory, allowing
the Resume feature to return the vehicle to
the previous speed. On the Tracker, when
the vehicles speed drops below 25 mph,
the previous set speed will not be retained
in memory. It is necessary to set a new
speed input. This is normal and does not
require repairs.
Diagnostics for other conditions, including
resistance specifications to bench test the
cruise control switch, are located in SI 2000.
Thanks to Donald B. Sherman
On some 1998-2002 S-10 and Sonoma
extended cab models with 4-cylinder engine,
owners may comment that the vehicle
vibrates at take off. Use