Range Rover P38
LAND ROVER V8
45
DESCRIPTION AND OPERATION
IAT SENSOR
The intake air temperature sensor utilises a thermistor
with a negative temperature co-efficient (as
temperature rises, thermistor resistance decreases).
The change in resistance causes a change in input
voltage at the ECM. The ECM converts the voltage
value it receives to provide an indication of the
temperature of the inlet air.
If the IAT sensor fails, the ECM substitutes a default
value for air temperature of 45
°
C (113
°
F). An IAT
sensor failure may result in the following symptoms
being experienced:
•
Catalyst monitoring affected due to exhaust
temperature model.
•
Warm-up ignition angle affected.
•
ISC speed adaption disabled
•
ISC actuator blocked test disabled
•
Fuelling adaptions disabled.
•
Condenser fan hot restart inhibited
An IAT sensor failure is likely to occur for the following
reasons:
•
Sensor open circuit.
•
Sensor signal line short circuit to vehicle 12V
supply or ground.
•
Damaged sensor element
•
Bad connection or increased resistance in wiring
harness.
If the IAT sensor should fail, the following fault codes
will be generated by the ECM diagnostics, which can
be retrieved by Testbook:
•
P0112 - (air temperature signal is less than the
minimum threshold - after a sufficient time (more
than three minutes) for exhaust warm-up has
been allowed).
•
P0113 - (air temperature signal greater than the
maximum threshold).
Throttle Position (TP) sensor - (from 99MY)
The TP sensor is located on the rear of the throttle
body assembly in the engine compartment and fixed
to its mounting studs by two screws.
The TP sensor is a potentiometer having a resistance
track that is connected to a stabilized 5V supply at
one end of its track and ground at the other end of the
track. The potentiometer wiper arm is connected to
the throttle plate assembly and provides a signal to
the ECM which is an analogue voltage between 0.3V
(closed throttle) and 4.5V (wide open throttle),
corresponding to the throttle valve angle. The TP
sensor connector terminals are gold plated for good
conductivity and corrosion resistance; care should be
exercised if it is necessary to probe the connector and
sensor terminals.
The TP sensor enables the ECM to determine the
throttle valve’s position and angular velocity. The ECM
uses the data from the throttle valve position for
determining intake-air volume, which it uses for
calculating the necessary fuel injection duration under
various operating conditions. The data from the
throttle valve’s angular velocity is used mainly for
acceleration/deceleration compensation. The ECM
also uses closed throttle position for idle speed control
in conjunction with road speed.
The TP sensor also supplies the ECM with information
to enable the overrun fuel shut off strategy to be
implemented. When the ECM receives closed throttle
information from the TP sensor, it closes the injectors
for the duration of the closed throttle time.