Avalanche 1500 2WD V8-5.3L VIN T (2002)
also a requirement to renew license plates in some areas.
Using a scan tool, the technician can observe the System Status, complete or not complete, in order to verify that the vehicle meets the criteria to comply
with local area requirements. Using the System Status display, any of the following systems or combination of systems may be monitored for I/M
Readiness:
^
The catalyst
^
The Evaporative Emission (EVAP) system
^
The Heated Oxygen Sensors (HO2S)
^
The HO2S heater
^
The Exhaust Gas Recirculation (EGR) system
^
The secondary air injection (AIR) system
IMPORTANT: The System Status display indicates only whether or not the test has been completed. The System Status display does not necessarily
mean that the test has passed. If a Failed Last Test indication is present for a DTC associated with one of the above systems, diagnosis and repair is
necessary in order to meet the I/M requirement. Verify that the vehicle passes all of the diagnostic tests associated with the displayed System Status prior
to returning the vehicle to the customer. Refer to the Typical Drive Cycle table, more than one drive cycle may be needed, to use as a guide to complete
the I/M System Status tests.
Typical Drive Cycle
Following a DTC info clear, System Status clears for one or all of these systems. Following a battery disconnect or a PCM replacement, all System
Status information clears.
Primary System Based Diagnostics
There are primary system-based diagnostics which evaluate the system operation and their effect on vehicle emissions. The primary system-based
diagnostics are listed below, with a brief description of the diagnostic functionality.
Oxygen Sensor Diagnosis
Diagnose the fuel control heated oxygen sensors (HO2S) for the following conditions:
^
Heater performance, heater current monitor
^
Response switches, number or switches R/L or L/R
^
Response time, time to switch R/L or L/R
^
Inactive signal, output steady at bias voltage - approximately 450 mV
^
Signal fixed high
^
Signal fixed low
Diagnose the catalyst monitor HO2S for the following functions:
^
Heater performance, heater current monitor
^
Signal fixed low
^
Signal fixed high
^
Inactive sensor
Heated Oxygen Sensors
The main function of the pre-catalyst HO2S is to provide the PCM with exhaust stream information in order to maintain proper fueling to hold emissions
within acceptable levels. These oxygen sensors are always located between the exhaust manifold and the 3-way Catalytic Converter (TWC). After the
sensor reaches the operating temperature, the sensor generates a voltage inversely proportional to the amount of oxygen present in the exhaust gases.
The PCM uses the signal voltage from the fuel control HO2S in a Closed Loop in order to adjust the fuel injector pulse width. While in a Closed Loop,
the PCM can adjust fuel delivery in order to maintain an air to fuel ratio which allows the best combination of emission control and driveability.
