This code appears when the oxygen sensor detects the fuel ratio has too little air and too much fuel. Something in the fuel system is causing the air and fuel to mix incorrectly.  

Trouble shooting should include the following:

• Dirty air filter
• Fuel is bad
• Thin air at high altitudes
• Fuel injector issues
• Fuel filter dirty and clogged
• Vacuum leak
• Faulty LPG vaporizer
• Faulty LPG regulator
• Faulty LPG mixer