GM Service Manual Online
For 1990-2009 cars only
Table 1: CNG Pressure vs Percent Full
Table 2: PWM Output

CNG Pressure vs Percent Full

kPa (psi)¹

-50°C (-18°F)²

-30°C (3°F)²

-9°C (23°F)²

11°C (43°F)²

32°C (54°F)²

53°C (84°F)²

73°C (105°F)²

93°C (125°F)²

114°C (146°F)²

134°C (166°F)²

156°C (187°F)²

2825 (410)

17%

15%

13%

12%

11%

11%

10%

9%

9%

8%

8%

5650 (819)

40%

34%

29%

26%

24%

22%

20%

19%

18%

17%

16%

8474 (1229)

79%

59%

49%

41%

38%

34%

31%

29%

27%

25%

24%

11299 (1638)

115%

87%

70%

56%

50%

45%

41%

38%

36%

33%

31%

14124 (2048)

122%

109%

85%

73%

65%

60%

53%

48%

45%

42%

39%

16949 (2458)

122%

122%

101%

88%

79%

71%

65%

58%

54%

50%

47%

19774 (2867)

122%

122%

116%

100%

90%

81%

75%

67%

63%

59%

55%

22599 (3277)

122%

122%

122%

112%

100%

92%

83%

76%

70%

66%

62%

25453 (3686)

122%

122%

122%

122%

109%

100%

90%

84%

78%

74%

70%

28248 (4096)

122%

122%

122%

122%

111%

103%

96%

90%

84%

80%

76%

¹This indicates the fuel pressure inside the CNG fuel tank.

²This indicates the temperature of the fuel inside the CNG fuel tank.

Use the table in order to determine the amount of fuel vs fuel tank capacity.

PWM Output

Percent Fuel¹

PWM Output²

10%

17

20%

33

30%

45

40%

52

50%

56

60%

59

70%

62

80%

64

90%

67

100%

70

¹ This is the percentage of fuel the gauge will display

²This is the PWM output required to display the percentage of fuel