Map a check-engine code to its root cause, recommended parts, and a related job.
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Root cause: The engine isn't reaching operating temperature — usually a stuck-open thermostat, low coolant, or a faulty coolant temperature sensor.
Recommended Parts
Random / Multiple Cylinder Misfire Detected
Root cause: One or more cylinders are misfiring. Common causes: worn spark plugs, failing ignition coils, clogged fuel injectors, vacuum leaks, or a failing mass airflow sensor.
Recommended Parts
System Too Lean (Bank 1)
Root cause: The engine is running lean — too much air, not enough fuel. Often a vacuum leak, dirty MAF sensor, weak fuel pump, or clogged fuel filter.
Recommended Parts
Catalyst System Efficiency Below Threshold (Bank 1)
Root cause: The catalytic converter is not cleaning exhaust efficiently. Could be a failing cat, an exhaust leak before the downstream O2 sensor, or a bad downstream O2 sensor.
Recommended Parts
Mass Air Flow Circuit Range / Performance
Root cause: The MAF sensor is reporting air flow outside the expected range. Often a dirty or failing MAF sensor, an intake leak, or a wiring issue.
Recommended Parts
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
Root cause: The upstream oxygen sensor's heater circuit has failed, causing slow sensor warm-up and poor cold-start fuel trim. Replace the upstream O2 sensor.
Recommended Parts