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GM MAP sensor Identification

I once got ripped off by ordering a 3Bar MAP sensor from some idiot on Ebay---he actually sent me a 1BAR! So....to make sure it didn't happen again, I did some research on how to identify a GM MAP sensor.

3 digit numbers for identification:
1 Bar: 039, 460, 883, 876, 153
2 Bar: 886, 012, 539, 609, 701
3 Bar: 749, 861

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The logic module uses the manifold absolute pressure (MAP) sensor to determine the absolute pressure (not the relative to atmospheric pressure) of the air inside the intake manifold and the atmosphere (barometric pressure).
This information is used to determine the density of the air entering the combustion chamber (in conjunction with the IAT(Intake Air temperature) sensor), which is used when calculating the proper air/fuel mixture for the engine, especially at WOT since the system is not in closed-loop at this time.
It is also used to help adjust the IAC(Idle Air Control) motor during idle.

It uses a silicon wafer that is thinner in the center (0.001") than around the edges (0.045"), which causes it to act as a diaphram.
It is mounted with a perfect vacuum beneath the chip so that the air pressure from the other side flexes the chip.
This flexing causes a change in resistance and the circuitry inside the sensor converts this to a voltage ranging from 0.02V to 4.94V when the output is pulled up towards 5V by the ECM(Electronic control module).

1 Bar MAP sensors are used on NA(naturally asperated) vehicles.
2 Bar MAP Sensors are used on forced induction vehicles(Turbo & Supercharged). They can measure up to 2x the apmospheric pressure(29.4psi), so that means it can measure up to 14.7psi boost(the atmosphere is 14.7psi + 14.7psi from the turbo/supercharger).
3 Bar MAP sensors can measure up to 44.1psi, which translates to 29.7psi boost from a Turbo/supercharger.

They all share a common pinout, although the connector keying may be different:
Pin A -- Ground
Pin B -- Sensor output
Pin C -- +5 volts

Places to order MAP Sensors
You can order them direct from:
www.SummitRacing.com
PN# MSD-2313 3bar MAP
PN# MSD-2312 2bar MAP
PN# MSD-2311 1bar MAP

or

www.GMPartsDirect.com
PN# 12223861 3bar MAP
PN# 16040609 2bar MAP
PN# 16137039 1bar MAP

The chart below describes the pressure-to-voltage relationship of the stock GM Turbo MAP sensor (2 bar):
 
Manifold Pressure
(relative sea level / absolute)
2 Bar
MAP Output
14.31psi / 29.01psi
4.90V
14.00psi / 28.70psi
4.84V
13.00psi / 27.70psi
4.67V
12.00psi / 26.70psi
4.50V
11.00psi / 25.70psi
4.33V
10.00psi / 24.70psi
4.16V
9.00psi / 23.70psi
3.99V
8.00psi / 22.70psi
3.82V
6.00psi / 20.70psi
3.47V
4.00psi / 18.70psi
3.13V
2.00psi / 16.70psi
2.79V
0.00psi / 14.70psi
2.45V
5.00inHg / 12.24psi
2.03V
10.00inHg / 9.78psi
1.61V
15.00inHg / 7.33psi
1.19V
20.00inHg / 4.87psi
0.77V
25.00inHg / 2.41psi
0.35V
29.10inHg / 0.40psi
0.02V

MAP sensor output based on altitude (Ignition "ON" and engine stopped)
AltitudeVoltage Range
MetersFeet--------------
Below 305Below 10003.8--5.5V
305--6101000--20003.6--5.3V
610--9142000-30003.5--5.1V
914--12193000--40003.3--5.0V
1219--15244000--50003.2--4.8V
1524--18295000--60003.0--4.6V
1829--21336000--70002.9--4.5V
2133--24387000--80002.8--4.3V
2438--27438000--90002.6--4.2V
2743--30489000-100002.5--4.0V
Low altitude = High Pressure = High Voltage


GM 1bar, 2bar, 3bar
1 PSI = 2.036" of Mercury (HG)
1" mercury = 0.4911541 PSI
Formula for the GM 3 Bar MAP sensor is (V*8.94)-14.53
I have no idea why it's 14.53 and not 14.696, [rounds up to 14.7] but it works out on GM's chart every time. It is possible that Detroit is slightly above sea level, and you can use 12.11 in the formula for 1 mile above sea level.
3Bar MAP

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