Preliminary Checks

Perform this procedure only after approved diagnostic procedures have isolated a CNG system component replacement or CNG system components require removal for other vehicle repairs. This vehicle is designed to start and operate on CNG. A switch-over to gasoline (the FIL is illuminated) should only occur under the following conditions:
^ The fuel tank pressure (FTP) sensor indicates the CNG fuel level is low.
Recommended action: Add CNG fuel.
^ When certain Alternative Fuel ECM DTCs set.
Recommended action: Perform the Diagnostic System Check - Alternative Fuels (Engine Controls).
^ Engine crank time exceeds 8 seconds.
Recommended action: Perform the Diagnostic System Check - Alternative Fuels (Engine Controls).
^ The ECT sensor indicates engine temperature is less than -12°C (10°F).
Recommended action: Perform a vehicle decel maneuver after meeting the following conditions:
- The coolant temperature is greater than 30°C (86°F)
- The FTP sensor indicates the CNG fuel level is OK.
- The engine speed is greater than 1,300 RPM.
- The TP sensor continuously indicates the throttle is less than 6 percent for at least 800 ms.
- The VSS indicates vehicle speed is greater than 56 km/h (35 mph).
^ Every 100th engine start. Recommended action: Perform a vehicle decel maneuver after meeting the following conditions:
- The coolant temperature is greater than 30°C (86°F)
- The FTP sensor indicates the CNG fuel level is OK.
- The engine speed is greater than 1,300 RPM.
- The TP sensor continuously indicates the throttle is less than 6 percent for at least 800 ms.
- The VSS indicates vehicle speed is greater than 56 km/h (35 mph).