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Home >> Chevrolet >> 2018 >> Impala Premier, Gas >> Repair and Diagnosis >> Accessories & Equipment >> Gauges & Instrument Panels >> Instrument Panel System Displays And Gauges >> Diagnostic Information and Procedures >> Fuel Gauge Malfunction (CNG Fuel Gauge) >> Circuit/System Testing

Circuit/System Testing

NOTE:

Circuit/System Verification must be performed before proceeding with Circuit/System Testing.

  1. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Disconnect the harness connector at the B257 Alternative Fuel Pressure Sensor. Test for less than 10 Ω between the low reference circuit terminal 1 and ground
    • If 10 Ω or greater 
    1. Disconnect the harness connector at the K20 Engine Control Module.
    2. Test for less than 2 Ω in the low reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
      • Go to next step: If less than 10 Ω 
  2. Ignition ON.
  3. Test for 4.8 - 5.2 V between the 5 V reference circuit terminal 3 and ground.
    • If less than 4.8 V 
    1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
    2. Test for infinite resistance between the 5 V reference circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the 5 V reference circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • If greater than 5.2 V 
    1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
    2. Test for less than 1 V between the 5 V reference circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K20 Engine Control Module.
    • Go to next step: If between 4.8 - 5.2 V 
  4. Test for 4.0 - 6.0V between the signal circuit terminal 2 and ground.
    • If less than 4.0 V 
    1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
    2. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • If greater than 6.0 V 
    1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K20 Engine Control Module.
    • Go to next step: If between 4.0 - 6.0V 
  5. Start engine and let idle at operating temperature in CNG mode.
  6. Verify scan tool Alternative Fuel Tank Pressure Sensor parameter is 0 Volts.
    • If Alternative Fuel Tank Pressure Sensor parameter is 0 Volts 

      Replace the B257 Alternative Fuel Tank Pressure Sensor.

    • Go to next step: If Alternative Fuel Tank Pressure Sensor parameter is not 0 Volts 
  7. Ignition OFF.
  8. Connect the harness connector at the B257 Alternative Fuel Tank Pressure Sensor, ignition ON.
  9. Start engine and let idle at operating temperature in CNG mode.
  10. Verify fuel gauge is reading accurately.
    • If CNG fuel gauge is displaying accurately 

      All OK.

    • Go to next step: If CNG fuel gauge is not reading accurately 
  11. Replace the K20 Engine Control Module.
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