MAP Sensor TTM1.0
What it does
An electronic sensing element converts engine vacuum
(or pressure for turbo/supercharged applications)
into an electrical reading which the ECU interprets
as an engine load signal. As engine load changes,
so does the engine’s inlet manifold vacuum,
the corresponding signal reflects this. The ECU uses
this information to calculate the engine’s ignition/fuel
system requirements.
How does it work?
Many different types of MAP sensor have been used
throughout the development of EMS. The most common
device in use today consists of a silicon chip (surprise,
surprise) into which a small diaphragm has been etched.
Small electro-deformation resistors measure any deflection
of this diaphragm; internal circuitry amplifies this
signal and sends the ECU the correct message.
Two different types of output have been used, linear
or digital. Linear types have a voltage that rises
or falls in line with manifold pressure/vacuum. Digital
types have a sine wave output which the frequency
changes in line with manifold pressure/vacuum.
It is now quite common to have a temperature sensor
built into the pressure sensor. This gives a separate
output to enable the ECU to calculate air/fuel density.
Traditionally MAP sensors were mounted under the
bonnet, often on the bulkhead. Modern versions are
located on the inlet manifold and due to their reduced
size are often overlooked.
Reasons for failure/testing:
As with other sensors, the component itself will
have a very long service life in ideal conditions,
it’s when it’s fitted under the bonnet
of a motor vehicle in real world conditions that things
start to go wrong.
They operate on low voltages (0-5v) and low output
signals; even the slightest wiring or poor connection
fault will cause an error. A short to 12 volts is
also quite a common problem caused by a wiring loom
or fuse box fault. Check the supply voltage and compare
with known data. A short to 12v will generally affect
all of the other engine-mounted 5 volt sensors and
damage may result. Ensure that the wiring and power
supply is checked before you renew the sensor to prevent
damage to the replacement sensor.
Check the output signals as close, electrically, to
the ECU as possible, (this ensures that the wires
and connectors are in good order) note the vacuum
and output readings and compare them to a known data
source.
The vacuum source is from the inlet manifold via
a small pipe, this often allows oil into the sensor,
which will cause its failure. Some manufacturers use
an in-line oil trap to prevent this from happening;
this trap can get blocked and will cause similar symptoms
to a failed sensor.
Note:
Ensure that the correct sensor is used as they are
easily damaged.
For further technical information
concerning MAP sensors please phone our technical
help line 01527 839307
