User Manual - Page 427

For 2001 XTERRA.

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Description
NGEC0279
SYSTEM DESCRIPTION
NGEC0279S01
Sensor Input Signal to ECM
ECM func-
tion
Actuator
Camshaft position sensor Engine speed
ECM IACV-AAC valve
Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
Ignition switch Start signal
Throttle position sensor Throttle position
PNP switch Park/Neutral position
Air conditioner switch Air conditioner operation
Power steering oil pressure switch Power steering load signal
Battery Battery voltage
Vehicle speed sensor Vehicle speed
Absolute pressure sensor Ambient barometric pressure
Intake air temperature sensor Intake air temperature
This system automatically controls engine idle speed to a specified
level. Idle speed is controlled through fine adjustment of the
amount of air which bypasses the throttle valve via IACV-AAC
valve. The IACV-AAC valve repeats ON/OFF operation according
to the signal sent from the ECM. The camshaft position sensor
detects the actual engine speed and sends a signal to the ECM.
The ECM then controls the ON/OFF time of the IACV-AAC valve
so that engine speed coincides with the target value memorized in
ECM. The target engine speed is the lowest speed at which the
engine can operate steadily. The optimum value stored in the ECM
is determined by taking into consideration various engine
conditions, such as during warm up, deceleration, and engine load
(air conditioner, power steering and cooling fan operation).
SEF040E
COMPONENT DESCRIPTION
NGEC0279S02
The IAC valve-AAC valve is moved by ON/OFF pulses from the
ECM. The longer the ON pulse, the greater the amount of air that
will flow through the valve. The more air that flows through the
valve, the higher the idle speed.
DTC P0505 IDLE AIR CONTROL VALVE (IACV) — AUXILIARY
AIR CONTROL (AAC) VALVE
KA24DE
Description
EC-427
FE
CL
MT
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
GI
MA
EM
LC
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