Diagnostic trouble code

How it is used

Usually shortened to DTC or simply called a fault code. Technicians read, record and clear codes with a scan tool. A code tells you where to start looking, not which part to replace, so always confirm it with tests.

Example sentences

1. The ECU stored diagnostic trouble code P0420: catalyst efficiency below threshold.

2. Write down every diagnostic trouble code before you clear them.

Common collocations

• read a diagnostic trouble code
• clear the codes
• stored DTC
• pending code

Related terms

• OBD-IIShort for On-Board Diagnostics, second generation: a standard self-diagnosis system with a 16-pin connector that lets any scan tool read emission-related fault codes and live data.
• scan toolA handheld device or laptop software that connects to the vehicle's diagnostic port to read and clear fault codes, view live data and run tests on control units.
• check engine lightThe amber engine-shaped warning light on the dashboard that comes on when the engine or emission control system detects a fault and stores a code.
• diagnoseTo find the cause of a fault by checking the symptoms, reading data and testing parts step by step, before any repair is made.
• ECUShort for electronic control unit (or engine control unit): a small computer that reads sensors and controls actuators, for example injection timing in an engine. Modern cars have dozens of them.

More terms: Diagnostics, Service and Repair

• service interval
• oil change
• misfire
• limp mode
• torque wrench
• jack up