<s>
The	O
manifold	B-Algorithm
absolute	I-Algorithm
pressure	I-Algorithm
sensor	I-Algorithm
(	O
MAP	B-Algorithm
sensor	I-Algorithm
)	O
is	O
one	O
of	O
the	O
sensors	O
used	O
in	O
an	O
internal	O
combustion	O
engine	O
's	O
electronic	O
control	O
system	O
.	O
</s>
<s>
Engines	O
that	O
use	O
a	O
MAP	B-Algorithm
sensor	I-Algorithm
are	O
typically	O
fuel	O
injected	O
.	O
</s>
<s>
The	O
manifold	B-Algorithm
absolute	I-Algorithm
pressure	I-Algorithm
sensor	I-Algorithm
provides	O
instantaneous	O
manifold	O
pressure	O
information	O
to	O
the	O
engine	O
's	O
electronic	B-Device
control	I-Device
unit	I-Device
(	O
ECU	O
)	O
.	O
</s>
<s>
A	O
typical	O
naturally	O
aspirated	O
engine	O
configuration	O
employs	O
one	O
or	O
the	O
other	O
,	O
whereas	O
forced	O
induction	O
engines	O
typically	O
use	O
both	O
;	O
a	O
MAF	O
sensor	O
on	O
the	O
Cold	O
Air	O
Intake	O
leading	O
to	O
the	O
turbo	O
and	O
a	O
MAP	B-Algorithm
sensor	I-Algorithm
on	O
the	O
intake	O
tract	O
post-turbo	O
before	O
the	O
throttle	O
body	O
on	O
the	O
intake	O
manifold	O
.	O
</s>
<s>
MAP	B-Algorithm
sensor	I-Algorithm
data	O
can	O
be	O
converted	O
to	O
air	O
mass	O
data	O
by	O
using	O
a	O
second	O
variable	O
coming	O
from	O
an	O
IAT	O
Sensor	O
(	O
intake	O
air	O
temperature	O
sensor	O
)	O
.	O
</s>
<s>
The	O
MAP	B-Algorithm
sensor	I-Algorithm
can	O
also	O
be	O
used	O
in	O
OBD	O
II	O
(	O
on-board	O
diagnostics	O
)	O
applications	O
to	O
test	O
the	O
EGR	O
(	O
exhaust	O
gas	O
recirculation	O
)	O
valve	O
for	O
functionality	O
,	O
an	O
application	O
typical	O
in	O
OBD	O
II	O
equipped	O
General	O
Motors	O
engines	O
.	O
</s>
<s>
If	O
the	O
throttle	O
is	O
opened	O
all	O
the	O
way	O
in	O
condition	O
2	O
,	O
the	O
manifold	B-Algorithm
absolute	I-Algorithm
pressure	I-Algorithm
will	O
increase	O
from	O
50	O
kPa	O
to	O
nearly	O
100	O
kPa	O
(	O
14.5	O
psi	O
,	O
29.53	O
inHG	O
)	O
,	O
about	O
equal	O
to	O
the	O
local	O
barometer	O
,	O
which	O
in	O
condition	O
2	O
is	O
sea	O
level	O
.	O
</s>
<s>
Engine	O
vacuum	B-General_Concept
is	O
the	O
difference	O
between	O
the	O
pressures	O
in	O
the	O
intake	O
manifold	O
and	O
ambient	O
atmospheric	O
pressure	O
.	O
</s>
<s>
Engine	O
vacuum	B-General_Concept
is	O
a	O
"	O
gauge	O
"	O
pressure	O
,	O
since	O
gauges	O
by	O
nature	O
measure	O
a	O
pressure	O
difference	O
,	O
not	O
an	O
absolute	O
pressure	O
.	O
</s>
<s>
The	O
engine	O
fundamentally	O
responds	O
to	O
air	O
mass	O
,	O
not	O
vacuum	B-General_Concept
,	O
and	O
absolute	O
pressure	O
is	O
necessary	O
to	O
calculate	O
mass	O
.	O
</s>
<s>
Note	O
:	O
Carburetors	O
are	O
largely	O
dependent	O
on	O
air	O
volume	O
flow	O
and	O
vacuum	B-General_Concept
,	O
and	O
neither	O
directly	O
infers	O
mass	O
.	O
</s>
<s>
Some	O
manufacturers	O
use	O
the	O
MAP	B-Algorithm
sensor	I-Algorithm
to	O
accomplish	O
this	O
.	O
</s>
<s>
The	O
MAP	B-Algorithm
sensor	I-Algorithm
is	O
then	O
used	O
for	O
rationality	O
checks	O
and	O
to	O
test	O
the	O
EGR	O
valve	O
.	O
</s>
<s>
The	O
way	O
they	O
do	O
this	O
is	O
during	O
a	O
deceleration	O
of	O
the	O
vehicle	O
when	O
there	O
is	O
low	O
absolute	O
pressure	O
in	O
the	O
intake	O
manifold	O
(	O
i.e.	O
,	O
a	O
high	O
vacuum	B-General_Concept
present	O
in	O
the	O
intake	O
manifold	O
relative	O
to	O
the	O
outside	O
air	O
)	O
the	O
powertrain	B-Device
control	I-Device
module	I-Device
(	O
PCM	O
)	O
will	O
open	O
the	O
EGR	O
valve	O
and	O
then	O
monitor	O
the	O
MAP	B-Algorithm
sensor	I-Algorithm
's	O
values	O
.	O
</s>
<s>
If	O
the	O
EGR	O
is	O
functioning	O
properly	O
,	O
the	O
manifold	B-Algorithm
absolute	I-Algorithm
pressure	I-Algorithm
will	O
increase	O
as	O
exhaust	O
gases	O
enter	O
.	O
</s>
<s>
MAP	B-Algorithm
sensors	I-Algorithm
measure	O
absolute	O
pressure	O
.	O
</s>
<s>
Thus	O
,	O
a	O
MAP	B-Algorithm
sensor	I-Algorithm
will	O
always	O
read	O
100	O
kPa	O
more	O
than	O
a	O
boost	O
sensor	O
measuring	O
the	O
same	O
conditions	O
.	O
</s>
<s>
A	O
MAP	B-Algorithm
sensor	I-Algorithm
will	O
never	O
display	O
a	O
negative	O
reading	O
because	O
it	O
is	O
measuring	O
absolute	O
pressure	O
,	O
where	O
zero	O
is	O
the	O
total	O
absence	O
of	O
pressure	O
.	O
</s>
<s>
Vacuum	B-General_Concept
is	O
measured	O
as	O
a	O
negative	O
pressure	O
relative	O
to	O
normal	O
atmospheric	O
pressure	O
.	O
</s>
<s>
Vacuum-Boost	O
sensors	O
can	O
display	O
negative	O
readings	O
,	O
indicating	O
vacuum	B-General_Concept
or	O
suction	O
(	O
a	O
condition	O
of	O
lower	O
pressure	O
than	O
the	O
surrounding	O
atmosphere	O
)	O
.	O
</s>
<s>
This	O
is	O
often	O
called	O
vacuum	B-General_Concept
pressure	O
when	O
referring	O
to	O
internal	O
combustion	O
engines	O
.	O
</s>
<s>
In	O
short	O
,	O
in	O
a	O
standard	O
atmosphere	O
most	O
boost	O
sensors	O
will	O
read	O
one	O
atmosphere	O
less	O
than	O
a	O
MAP	B-Algorithm
sensor	I-Algorithm
reads	O
.	O
</s>
