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Home >> Pontiac >> 2004 >> Sunfire Standard >> Repair and Diagnosis >> Accessories & Equipment >> Gauges & Instrument Panels >> Instrument Panel System Displays, Gauges And Console - Bi-Fuel (CNG) >> Diagnostic Information and Procedures >> Fuel Gauge Inaccurate or Inoperative - Alternative Fuels >> Diagnostic Aids

Diagnostic Aids

If the vehicle operators concern is uniquely related to fast filling of the CNG fuel tank review the following with the vehicle operator:

The CNG fuel tank will not completely fill during a fast-fill, due to the expansion of the fuel. The fuel gage will display full as long as the fuel remains hot. The fuel gage display will decrease as the fuel cools.

Fuel Gauge Inaccurate or Inoperative - Alternative Fuels

Step Action Values Yes No
1 Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Alternative Fuels (Engine Controls)
2
IMPORTANT: Verify that the customers concern is not a normal operating condition. Refer to Diagnostic Aids.
Is the customers concern a normal operating condition?		 - System OK Go to Step 3 
3
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the Fuel Gage Select Switch parameter with a scan tool.
  3. Apply and release the fuel gage select switch several times.
Does the parameter indicate the switch is operating as commanded?		 - Go to Step 4  Go to Step 9 
4 Command the fuel gage between full and empty with the scan tool Instrument Panel Special Functions.
Does the fuel gage operate as commanded?		 - Go to Step 5  Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gages and Console in the Cavalier and Sunfire service information.
5
IMPORTANT: Fast-filling the CNG fuel tank causes the fuel to heat-up and expand.
The fuel temperature may remain hotter than the ambient (IAT) temperature for up to 3 hours after filling.
  1. Observe the Fuel Temperature Sensor and the IAT Sensor data displays with a scan tool.
  2. Compare the temperature displays.
Does each sensor indicate the same temperature plus or minus the specified value?		 20°C (35°F) Go to Step 6  Go to Step 18 
6 Observe the Fuel Tank Pressure Sensor voltage data parameter with the scan tool.
Does the parameter indicate a voltage less than the specified value?		 4.8 V Go to Step 7  Go to Step 14 
7
IMPORTANT: Fast-filling the CNG fuel tank causes the fuel to heat-up and expand.
The fuel tank pressure may DECREASE by up to 800 psi within three hours of fast filling.
  1. Observe the Fuel Tank Pressure Sensor data parameter with a scan tool.
  2. Verify the amount of CNG fuel pressure in the fuel tank by filling the CNG fuel tank to full at a CNG dispensing station.
  3. Compare the Fuel Tank Pressure Sensor data parameter to the Compressed Natural Gas (CNG) Temperature vs Percent Full after the tank is full.
Does the FTP sensor accurately indicate a full tank?		 - Go to Step 8  Go to Step 19 
8
  1. Observe the Fuel Tank Pressure Sensor data parameter with a scan tool.
  2. Start and idle the engine.
  3. Command the high pressure lock-off (HPL) solenoid closed with the scan tool.
  4. Observe the Fuel Tank Pressure sensor data parameter while the HPL is commanded closed.

    The fuel pressure should slowly and smoothly drop until the vehicle switches to gasoline (KL6) or stalls.

Did the fuel pressure drop smoothly and consistently?		 - System OK Go to Step 19 
9 Does the scan tool always indicate released? - Go to Step 11  Go to Step 10 
10
  1. Disconnect the fuel gage select switch connector.
  2. Observe the Fuel Gage Select Switch data parameter with a scan tool.
Does the parameter indicate released?		 - Go to Step 20  Go to Step 13 
11
  1. Disconnect the fuel gage select switch connector.
  2. Connect the fuel gage select switch signal circuit terminal to the ignition power circuit terminal with a fused jumper.
  3. Observe the Fuel Gage Select Switch parameter with a scan tool.
Does the parameter indicate applied?		 - Go to Step 16  Go to Step 12 
12 Test the Fuel Gage Select Switch Signal circuit for an open condition. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the Cavalier and Sunfire service information.
Did you find and correct the condition?		 - Go to Step 22  Go to Step 17 
13 Test the Fuel Gage Select Switch Signal circuit for a short to B+ condition. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the Cavalier and Sunfire service information.
Did you find and correct the condition?		 - Go to Step 22  Go to Step 21 
14
  1. Connect a jumper wire between each of the terminals in the FTP sensor harness connector and the corresponding terminal at the FTP sensor. Refer to Using Connector Test Adapters in Wiring Systems in the Cavalier and Sunfire service information.
  2. Measure the voltage from the FTP sensor low reference ground circuit jumper wire terminal to a good ground with a DMM. Refer to Measuring Voltage Drop in Wiring Systems in the Cavalier and Sunfire service information.
Is the voltage more than the specified value?		 0.2 V Go to Step 15  Go to Step 19 
15 Test the fuel tank pressure sensor ground circuit for an open condition. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the Cavalier and Sunfire service information.
Did you find and correct the condition?		 - Go to Step 22  Go to Step 17 
16 Inspect for proper terminal contact at the fuel gage switch connector. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems in the Cavalier and Sunfire service information.
Did you find and correct the condition?		 - Go to Step 22  Go to Step 20 
17 Inspect for proper terminal contact at the PCM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems in the Cavalier and Sunfire service information.
Did you find and correct the condition?		 - Go to Step 22  Go to Step 21 
18 Replace the fuel tank temperature sensor.
The temperature sensor is not Serviceable separately from the HPL. Refer to High Pressure Lock-Off (HPL) Solenoid Replacement in Engine Controls.
Did you complete the replacement?		 - Go to Step 22  -
19 Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement in Engine Controls.
Did you complete the replacement?		 - Go to Step 22  -
20 Replace the fuel gage select switch. Refer to Fuel Gage Selector Switch/Fuel Indicator Lamp Replacement - Alternative Fuels  .
Did you complete the replacement?		 - Go to Step 22  -
21 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls in the Cavalier and Sunfire service information.
Did you complete the replacement?		 - Go to Step 22  -
22
  1. Connect any disconnected components, fuses, etc.
  2. With the scan tool, clear DTC Information from the PCM.
  3. Turn the ignition OFF for 30 seconds.
  4. Start the engine and operate the vehicle.
  5. Observe the MIL and the Fuel Indicator Lamp - KL6 only.
  6. Observe vehicle performance and driveability.
  7. After operating the vehicle inspect the PCM for stored DTCs.
Does the vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs?		 - System OK Go to Diagnostic System Check - Alternative Fuels (Engine Controls)
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