Possible causes – Faulty O2 Sensor– High fuel pressure– Faulty Mass Air Flow (MAF) Sensor– O2 Sensor harness is open or shorted– O2 Sensor circuit poor electrical connection Symptoms – Engine Light ON (or Service Engine Soon Warning Light) AUDI Related P1139 code 1998 AUDI A4 Fuel System, Other 1998 AUDI A6 Fuel System, Other…