P1151 OBD Code Definition:
P1151 Lack Of HO2S21 Switch – Sensor Indicates Lean
P1151 OBD Code Description:

Possible Symptoms

• Malfunction Indicator Lamp (MIL) active
• Engine Light ON (or Service Engine Soon Warning Light)

Possible Causes

• Intake System faulty/leaking
• Fuel Pressure, Fuel Pressure Regulator and Fuel Pump faulty
• Fuel Injectors faulty/leaking
• Exhaust System faulty/leaking
• Activated-Charcoal Filter/System faulty/leaking
• Secondary Air Injection System faulty/leaking
• Lambda/Oxygen Sensor(s) before Catalytic Converter faulty
• Lambda/Oxygen Sensor(s) after Catalytic Converter faulty

Possible Solutions

• Check Intake System for Leaks
• Check Fuel Pressure, Fuel Pressure Regulator and Fuel Pump
• Check Fuel Injectors
• Check Exhaust System for Leaks
• Check Activated-Charcoal Filter/System
• Check Secondary Air Injection System
• Check Lambda/Oxygen Sensor(s) before Catalytic Converter
• Check Lambda/Oxygen Sensor(s) after Catalytic Converter