Trouble Codes
WARNING
To avoid personal injury and/or vehicle damage, refer to the service precautions at the
beginning of this section.
General Information
Scan Tools
All late-model vehicles utilize computers to monitor and control the functions of on-board
systems. These modules are known by many names such as Engine Control Unit (ECU),
Engine Control Module (ECM), Powertrain Control Module (PCM), Transmission Control
Module (TCM) and Vehicle Control Module (VCM). When problems occur in control circuits
these modules record a diagnostic trouble code that can be used to help solve the
problem. There is also freeze frame data and an OBD status report available to the
technician. Over the years there have been many different variations of systems, each with
their own unique way of retrieving these codes. On a good number of the older systems
the stored codes were flashed on check engine lights (found in the dash cluster) once a
small jumper wire was placed across the proper diagnostic terminals. However the use of
a hand-held scan tool was still preferred for these systems by dealership service
departments.
For some models produced during the 1995 model year and on almost every single 1996
and later model a new form of trouble code reporting was developed which required the
use of a scan tool. On Board Diagnostic-II (OBD-II) compliant vehicles use a 5 digit, alpha-
numeric code which would be difficult or impossible to read using a flashing light. Trouble
code reading on an OBD-II compliant vehicle requires a scan tool. Flashing trouble codes
are a thing of the past.
The scan tool allows any stored codes to be read from the ECM. The tool also allows the
operator to view the data being used by the engine management computer while the
engine is running, or with the engine OFF and the key ON. This ability has obvious
diagnostic advantages; the use of the scan tool is frequently required for component
testing. The scan tool makes collecting information easier; the data must be correctly
interpreted by an operator familiar with the vehicles operating systems.
An example of the usefulness of the scan tool may be seen in the case of a temperature
sensor which has changed its electrical characteristics. The computer module is reacting
to an apparently warmer engine (causing a driveability pro
blem) but the sensor’s voltage
has not changed enough to set a fault code. The voltage signal being sent to the module
may be viewed by connecting a scan tool. Comparison to normal values or a known good
vehicle reveals the problem quickly.
Содержание TrailBlazer
Страница 1: ......
Страница 26: ...Fig 3 Typical body and undervehicle maintenance locations Refer to chart for descriptions ...
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Страница 59: ...Cylinder head bolt removal and installation 32 Remove and discard the bolts from the cylinder head ...
Страница 175: ...Spring free length check Valve spring squareness check ...
Страница 192: ...Front of piston mark ...
Страница 361: ...5 3L Engine Except Saab Underhood Fuse Block 2003 2005 Early Production ...
Страница 469: ...Removing the outer band from the CV boot Removing the inner band from the CV boot ...
Страница 470: ...Removing the CV boot from the joint housing Clean the CV joint housing prior to removing boot ...
Страница 471: ...Removing the CV joint housing assembly Removing the CV joint ...
Страница 472: ...Inspecting the CV joint housing Removing the CV joint outer snap ring ...
Страница 473: ...Checking the CV joint snap ring for wear CV joint snap ring typical ...
Страница 474: ...Removing the CV joint assembly Removing the CV joint inner snap ring ...
Страница 475: ...Installing the CV joint assembly typical ...
Страница 506: ...Tie Rod End Removal Installation Inner Tie Rod End To Remove Inner tie rod assembly Magnasteer ...
Страница 553: ...9 Torque the lug nuts to specification 10 Lower the vehicle ...
Страница 556: ...Toe in Frame Misalignment Frame misalignment ...
Страница 588: ...Bleeding caliper ...
Страница 596: ...Inboard brake pad removal and installation 10 Remove the inboard brake pad from the brake caliper ...
Страница 624: ...Manifold gauge set components Refrigerant recovery recycling station ...
Страница 662: ...Lower instrument panel retaining volts 25 Remove the lower retaining bolts from the instrument panel I P ...
Страница 676: ...A C Specifications ...
Страница 677: ......