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Knock Sensor (KS) System Description
You can diagnose all of the sensors and most of the
input circuits with a scan tool. Within this section is a
short description of how to use a scan tool wherever
possible to diagnose these circuits. You can also use the
scan tool to compare the values for an engine that is
running normally with the engine you are diagnosing.
The knock sensor (KS) system detects engine knocking
or pinging. The ECM will retard the spark timing based
on the signals from the KS system. The KS produce an
AC voltage that is sent to the engine control module
(ECM). The amount of the AC voltage produced is
proportional to the amount of knock.
The ECM monitors the voltage of the sensors after each
cylinder has fired.
If knock occurs in any of the cylinders, the ignition will be
retarded for that particular cylinder. If the knocking then
stops, the ignition will be restored to what it was before
in steps.
Should knocking continue in the same cylinder in spite of
the ignition being retarded, the ECM will retard the
ignition an additional steps, and so on, up to a maximum
of 12 degrees of retard. The ignition will also be retarded
at high ambient temperatures in order to counteract
knocking tendencies provoked by high intake air
temperatures.
Should either bank 1 or bank 2 sensor fail to work, or
should an internal circuit problem occur, the ignition
timing will then use a default strategy. The default
strategy will retard the ignition the maximum allowed
amount to protect the engine from possible damage.
Throttle Actuator Control (TAC) System
Description
The throttle actuator control (TAC) system is used to
improve emissions, fuel economy, and driveability. The
TAC system eliminates the mechanical link between the
accelerator pedal and the throttle plate. The TAC system
eliminates the need for a cruise control module and idle
air control motor. The following is a list of TAC system
components:
• The accelerator pedal assembly includes the following
components:
– The accelerator pedal
– The accelerator pedal position (APP) sensor 1
– The APP sensor 2
• The throttle body assembly includes the following
components:
– The throttle position (TP) sensor 1
– The TP sensor 2
– The throttle actuator motor
– The throttle plate
• The engine control module (ECM)
Engine Electrical Devices:
The ECM monitors the driver demand for acceleration
with 2 APP sensors. The APP sensor 1 signal voltage
range is from about 0.98-4.16 volts as the accelerator
pedal is moved from the rest pedal position to the full
pedal travel position. The APP sensor 2 range is from
about 0.49-2.08 volts as the accelerator pedal is moved
from the rest pedal position to the full pedal travel
position. The ECM processes this information along with
other sensor inputs to command the throttle plate to a
certain position.
The throttle plate is controlled with a direct current motor
called a throttle actuator control motor. The ECM can
move this motor in the forward or reverse direction by
controlling battery voltage and/or ground to 2 internal
drivers. The throttle plate is held at a 7 percent rest
position using a constant force return spring. This spring
holds the throttle plate to the rest position when there is
no current flowing to the actuator motor.
The ECM monitors the throttle plate angle with 2 TP
sensors. The TP sensor 1 signal voltage range is from
about 4.86-0.86 volts as the throttle plate is moved from
0 percent to wide open throttle (WOT). The TP sensor 2
voltage range is from about 0.82-4.14 volts as the
throttle plate is moved from 0 percent to WOT.
The ECM performs diagnostics that monitor the voltage
levels of both APP sensors, both TP sensors, and the
throttle actuator control motor circuit. It also monitors the
spring return rate of both return springs that are housed
internal to the throttle body assembly. These diagnostics
are performed at different times based on whether the
engine is running, not running, or whether the ECM is
currently in a throttle body relearn procedure.
Every ignition cycle, the ECM performs a quick throttle
return spring test to make sure the throttle plate can
return to the 7 percent rest position from the 0 percent
position. This is to ensure that the throttle plate can be
brought to the rest position in case of an actuator motor
circuit failure. Observe, under cold conditions, the ECM
commands the throttle plate to 7 percent with the ignition
ON and the engine OFF to release any ice that may
have formed on the throttle plate.
1C-7
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Troubleshooting
