Intake Air Temperature (Iat) Sensor; Knock Sensor - Isuzu 1999 RODEO Workshop Manual

result in lower sensor response.
incorrect catalyst monitor diagnostic results.
Legend
(1) Bank 1 Sensor 1 (Fuel Control)
(2) Catalytic Converter
(3) Bank 1 Sensor 2 (Catalyst Monitor)
(4) Bank 2 Sensor 1 (Fuel Control)
(5) Bank 2 Sensor 2 (Catalyst Monitor)

Intake Air Temperature (IAT) Sensor

The intake air temperature (IAT) sensor is a thermistor
which changes its resistance based on the temperature of
air entering the engine. Low temperature produces a high
resistance of 100,000 ohms at –40°C (–40°F). High
temperature causes low resistance of 70 ohms at 130°C
(266°F) . The PCM supplies a 5-volt signal to the sensor
through a resistor in the PCM and monitors the signal
voltage. The voltage will be high when the incoming air is
cold. The voltage will be low when the incoming air is hot.
By measuring the voltage, the PCM calculates the
RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS
This may cause
TS24067
TS23365A
incoming air temperature. The IAT sensor signal is used
to adjust spark timing according to the incoming air
density.
The Tech 2 displays the temperature of the air entering
the engine. The temperature should read close to the
ambient air temperature when the engine is cold and rise
as underhood temperature increases. If the engine has
not been run for several hours (overnight), the IAT sensor
temperature and engine coolant temperature should read
close to each other. A fault in the IAT sensor circuit will set
DTC P0112 or DTC P0113.

Knock Sensor

Insufficient gasoline octane levels may cause detonation
in some engines. Detonation is an uncontrolled explosion
(burn) in the combustion chamber. This uncontrolled
explosion results from a flame front opposite that of the
normal flame front produced by the spark plug. The
rattling sound normally associated with detonation is the
result of two or more opposing pressures (flame fronts)
colliding within the combustion chamber.
detonation is sometimes considered normal, but heavy
detonation could result in engine damage.
A knock sensor system is used to control detonation. This
system is designed to retard spark timing up to 20
degrees to reduce detonation in the engine. This allows
the engine to use maximum spark advance to improve
driveability and fuel economy.
The knock sensor system has two major components:
f The knock sensor (KS) module.
f The knock sensor.
The knock sensor, mounted in the engine block near the
cylinders, detects abnormal vibration in the engine. The
sensor produces an AC output signal of about 10
millivolts. The signal amplitude and frequency are
dependent on the amount of knock being experienced.
The signal voltage increases with the severity of the
knock. This signal voltage is input to the PCM. The PCM
then retards the ignition control (IC) spark timing based
on the KS signal being received.
The PCM determines whether knock is occurring by
comparing the signal level on the KS circuit with the
voltage level on the noise channel. The noise channel
allows the PCM to reject any false knock signal by
indicating the amount of normal engine mechanical noise
present. Normal engine noise varies depending on the
engine speed and load. If the voltage level on the KS
noise channel circuit is below the range considered
normal, DTC P0327 will set, indicating a fault in the KS
circuit or the knock sensor. If the PCM determines that an
abnormal minimum or maximum noise level is being
experienced, DTC P0325 will set.
The PCM contains a knock sensor (KS) module. The KS
module contains the circuitry which allows the PCM to
utilize the KS signal and diagnose the KS sensor and the
KS circuitry. If the KS module is missing or faulty, a
continuous knock condition will be indicated, and the
PCM will set DTC P0325.
Although it is a plug-in device, the KS module is not
replaceable. If the KS module is faulty, the entire PCM
must be replaced.
6E2–493
Light