DTC U1099 Buick

Description

Engine started, battery voltage must be at least 11.5v, all electrical components must be off, parking brake must be engaged (to keep daytime driving lights off), automatic transmission selector must be in park, the exhaust system must be properly sealed between the catalytic converter and the cylinder head, coolant temperature must be at least 80 degrees Celsius and oxygen sensor heaters for oxygen sensors before the catalytic converter must be functioning properly and the ground between the engine and the chassis must be well connected. The ECM detected an unexpected voltage condition on the EVAP circuit when the device was cycled On Off during testing.