The following is a complete list of codes to help you diagnose your check engine light. OBD 0/1/2 CEL CODES: 0 - ECU - Faulty ECU or ECU ROM Diagnostic Proceedure. 1 - O2A - Oxygen sensor #1. 2 - O2B - Oxygen sensor #2. 3 - MAP - manifold absolute pressure sensor. 4 - CKP - crank position sensor.