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EVAP Vacuum/Pressure Reference Sheets

  • Atmospheric Pressure Barometric Pressure= Approx. 14.7 Psi, 29.9 In Hg, 1 Bar, 100kPa
  • Gauge vs Absolute Pressure: Gauge pressure has Atmospheric pressure equal to zero and reads pressure/vacuum from that zero mark, while Absolute pressure (actual pressure) is not at zero and reads actual pressure.

EVAP Conversion Tables

These Tables display a very narrow range Pressure/Vacuum. Typical EVAP system pressure or vacuum is only approx. .75 InHg. (For example, normal engine manifold vacuum is 20 InHg gauge, or 10 InHg absolute) Therefore these tables only show what you might see during normal EVAP system testing or operation. (Using shop air or anything high pressure or vacuum is beyond the safe limits of an EVAP system!)

Gauge Pressure/Vacuum Conversion Table

In HgIn H2OMm HgmBarPSIkPa
000000
0.11.362.533.380.050.34
0.22.715.076.750.10.68
0.34.077.610.130.151.01
0.45.4310.1313.510.21.35
0.56.7912.6616.880.251.69
0.68.1415.220.260.292.03
0.79.517.7323.640.342.36
0.810.8620.2627.020.392.7
0.912.2122.7930.390.443.04
113.5725.3333.770.493.38
1.114.9327.8637.150.543.72
1.216.2830.3940.520.594.05
1.317.6432.9343.90.644.4
1.41935.4647.270.694.73
1.520.363850.650.745.07
1.621.7140.5254.030.785.4
1.723.0743.0557.410.835.74

(Scan tool PIDs is implied for vacuum)

Absolute Pressure Conversion Table

In HgIn H2OMm HgmBarPSIkPa
29.93406.16758.03101114.66101.07
29.9405.76757.7100914.64100.96
29.8404.4754.74100614.59100.63
29.7403.04752.2100314.54100.29
29.6401.68749.67100014.4999.96
29.5400.33747.1499614.4499.61
29.4398.97744.6199214.3999.28
29.3397.61744.298914.3598.94
29.2396.25741.798614.398.6
29.1394.89737.0198214.2598.26
29393.54734.4797914.297.93
28.9392.18731.9497514.1597.59
28.8390.83729.496914.197.25
28.7389.47726.8796914.0596.91
28.6388.11724.349651496.57
28.5386.75721.8196213.9596.24
28.4385.39719.2795813.995.9
28.3384.04716.7495513.8695.56

Fuel Tank Pressure Sensor Specifications

Polarity- All manufactures (FTP) sensors have the same polarity except for GM

  • ALL Except GM: Voltage falls with vacuum and rises with pressure
  • GM: Voltage rises with vacuum and falls with pressure

GM - Typical FTP voltage to Pressure Table

FTP VoltageIndicated PressureFTP VoltageIndicated Pressure
0.5 Volts5.0- In H2O 3.1 Volts-8.6- In H2O
1.0 Volts2.6- In H2O 3.3 Volts-9.7- In H2O
1.5 Volts0 In -H2O 3.5 Volts-10.8- In H2O
2.0 Volts-2.5- In H2O 3.8 Volts-12.9- In H2O
2.7 Volts-6.7- In H2O 4.2 Volts-14.5- In H2O
2.9 Volts-7.8 -In H2O 4.5 Volts-16- In H2O

(Italics voltage represents Cap-Off value)

Fuel Tank Pressure Senor Cap-Off Values (+/-) 200 mV

ManufacturerCap-Off Voltage
Acura, Ford, Honda, Hyundai, Kia, Subaru2.5 Volts
Mazda2.6 Volts
Nissan, Infiniti3.3, 3.8, or 4.2 Volts
Toyota, Lexus, Scion3.3 Volts
General Motors1.5 Volts
2.9 Volts-7.8 -In H2O

Cap-Off values represent what sensors should read at atmospheric pressure