Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGauges, Warning Devices, and Driver Information Systems Diagnosis and RepairEasy
A customer complains that the 'Check Engine' light on their vehicle illuminates, and a scan tool retrieves Diagnostic Trouble Code (DTC) P0455. Which of the following is the most likely cause?
- AA faulty oxygen sensor
- BA loose or missing fuel cap
- CLow engine coolant level
- DA clogged catalytic converter
Show answer & explanationAnswer & explanation
Correct answer: B. A loose or missing fuel cap
DTC P0455 indicates a large leak in the Evaporative Emission Control (EVAP) system. The most common and easiest to fix cause of a large EVAP leak is a loose or missing fuel cap.
Why the other options are wrong
- A. A faulty oxygen sensor would typically set codes like P0133, P0135, P0171, or P0172, related to fuel trim or sensor performance.
- C. Low engine coolant level would typically trigger an engine overheating warning or specific coolant-related codes, not P0455.
- D. A clogged catalytic converter would usually set codes like P0420 or P0430, indicating catalyst efficiency issues.
DTC P0455
Diagnostic Trouble Code P0455 indicates a large leak detected in the Evaporative Emission Control (EVAP) system.
- EVAP system prevents fuel vapors from escaping into the atmosphere.
- A common cause is a loose or missing fuel cap.
- Other causes can include a cracked EVAP hose or a faulty purge valve.
Memory trick: EVAP 'Escape' means gas cap 'Gap'.