2006 Buick Lucerne CXS 4.6L Northstar V8 - P2A00, P0412, P0300 Fault Codes: Rough Idle, Poor Acceleration & Misfire
I own a 2006 Buick Lucerne CXS with a 4.6L Northstar V8 engine that is currently experiencing severe idle roughness, difficulty accelerating, and noticeable loss of power. The vehicle is throwing three diagnostic trouble codes: P2A00 (Oxygen Sensor Circuit Range/Performance - Bank 1 Sensor 1), P0412 (Secondary Air Injection System Switching Valve A Circuit Fault), and P0300 (Random/Multiple Misfire Detected). I've already replaced the air check/shutoff valve and the bank 1 sensor 1 oxygen sensor. The car also requires a new ground wire under the hood, and there are minor electrical symptoms present but no major faults. The original engine was swapped in at around 83K miles and has otherwise performed well—this issue appears to be isolated. I'm seeking expert advice on how to properly diagnose and resolve these codes, as this vehicle serves as my daily driver.
Prioritize addressing P0412 before tackling P2A00. With an oxygen sensor issue, the P0300 misfire could be a result of GIGO (Garbage In, Garbage Out) due to inaccurate sensor readings. • DTC P0412: Indicates a fault in the AIR valve relay coil circuit. Have you checked the fuses and relays for the air injection system? They are typically located in the underhood fuse box. Also verify voltage at the AIR solenoids. For P0300, inspect the B1S1 oxygen sensor voltage readings—check the engine temperature (ECT), mass airflow (MAF), and manifold absolute pressure (MAP) sensors to ensure accurate input data is being received.