Range Rover P38
19
FUEL SYSTEM
NEW RANGE ROVER
44
DESCRIPTION AND OPERATION
When the intake air passes the heated element, it
cools it down, so lowering the resistance of the hot
film element. In order to maintain the same
temperature, the circuit to the heated element has to
supply more current. The change in current causes a
corresponding change in potential difference to be
detected in the monitoring circuit. This change is
supplied to the ECM as a voltage between 0 and 5V,
where it is processed by the ECM’s internal mapping
to interpret the data as a measure of the mass of air
flow.
The measured air mass flow is used by the ECM to
determine the fuel quantity to be injected in order to
maintain the stoichiometric air:fuel mixture for
optimum engine performance and low emissions.
The MAF sensor receives a power supply via the
engine compartment fusebox, and a 5V reference
signal from the ECM. The MAF sensor and the IAT
sensor share a common ground connection and each
provide a separate signal input to the ECM.
CAUTION: Do not apply 12 V directly to the
5 V supply terminal, this will destroy the
internal circuitry. The connector terminals
are silver plated - avoid probing with multimeter
test leads.
If the MAF sensor fails, the ECM implements a
backup strategy which is based on throttle angle, air
temperature and engine speed. A MAF sensor failure
may result in the following symptoms being
experienced:
•
The engine rpm may relapse slightly during
driving and then recover.
•
Difficulty in starting and/or frequent stalling of
engine.
•
Poor throttle response
•
Degraded engine performance.
•
Emissions control and idle speed control
inoperative.
•
MAF sensor signal offset.
A MAF sensor failure is likely to occur for the following
reasons:
•
Sensor open circuit of voltage supply, signal or
ground lines.
•
Short circuit of signal line to vehicle supply or
ground.
•
Contaminated / damaged sensor element.
•
Air leak after the MAF sensor.
•
Inlet air restriction.
•
Poor connection or resistance in wiring harness
causing signal offset.
If the MAF sensor should fail, the following fault codes
will be generated by the ECM diagnostics, which can
be retrieved by Testbook:
•
P0102 - (MAF signal less than the speed
dependent minimum threshold).
•
P0103 - (MAF signal greater than the speed
dependent maximum threshold).
Intake-air density varies with temperature, the ECM
needs to be aware of these changes so that corrective
calculations can be incorporated into the ECM’s
fuelling and ignition timing strategies. The intake air
temperature value is also used by the ECM as a
reference when implementing compensation for an
ECT failure.
