Range Rover P38
LAND ROVER V8
21
DESCRIPTION AND OPERATION
Mass air flow (MAF) sensor - (up to 99MY)
The ’hot wire’ type mass air flow sensor is mounted
rigidly to the air filter and is connected by flexible hose
to the plenum chamber inlet. The MAF sensor is a hot
wire anenometer. The main sensing element of the
sensor is a heated wire, positioned in the stream of
intake air. Changes in intake air flow changes the
temperature, and hence resistance, of the wire. The
ECM measures this change in resistance and
calculates the amount of air flowing into the engine.
As there is no default strategy, failure will result in the
engine starting, and dying when it reaches 550
rev/min, when the ECM detects no MAF sensor
signal. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
Intake Air Temperature (IAT) sensor - (up to 99MY)
The IAT sensor is another resistive sensor, located in
the body of the air cleaner. The sensor resistance
varies with changes in air temperature. The signal
from the IAT sensor is used to retard the ignition
timing if the air temperature rises above 55
°
C. If the
sensor is disconnected or failure occurs, a default
value will be used by the system. The default value
selected will represent nominal operating conditions.
The fault may not be evident to the driver, there may
be slight power loss in high ambient temperatures.
The fault is indicated by illumination of the malfunction
indicator light (MIL) on North American specification
vehicles.
Throttle Position (TP) sensor - (up to 99MY)
The throttle position sensor is mounted on the throttle
body in line with the throttle plate shaft. The sensor is
a variable resistor, the signal from which (0 - 5V)
informs the ECM of the actual position of the throttle
disc and the rate of change of throttle position. This
information is used by the ECM for regulation of
acceleration enrichment fuelling. Sensor failure will
adversely affect the acceleration performance. The
closed throttle voltage is continuously monitored and
updated when engine conditions indicate that the
throttle is closed.
The GEMS ECM performs a throttle potentiometer
range check by cross checking with the measured air
flow. If the two values do not correlate and fuelling
feedback indicates that fuelling and therefore airflow is
correct, the potentiometer is assumed to have failed.
In the event that a fault is detected, GEMS supplies a
default value dependent on air flow.
The throttle angle is also supplied to the gearbox
ECM, the loss of this signal will result in poor gear
change quality and loss of kickdown.
WARNING: If the throttle potentiometer is
changed, it is necessary to reset the
closed throttle voltage.
Fault codes:
•
P0121 - Throttle potentiometer signal
inconsistent with MAF, IACV, air temperature
and engine rpm.
•
P0122 - Throttle potentiometer circuit low input
•
P0123 - Throttle potentiometer circuit high input
