Automotive Diagnostic Trouble Code | DTCs and their meanings

A Diagnostic Trouble Code (DTC) is a code stored in a vehicle’s onboard diagnostic system (OBD) when it detects a malfunction. These codes are used by technicians to identify and troubleshoot issues with a vehicle’s components or systems.

🔧 Understanding DTC Structure

DTCs follow a standard format, especially for OBD-II vehicles (1996 and newer in the U.S.):

Example: P0301

• First Character (System)

  • P – Powertrain (engine/transmission)

  • B – Body

  • C – Chassis

  • U – Network/Communication

• Second Character

  • 0 – Generic (SAE standard)

  • 1 – Manufacturer-specific

• Third Character (Subsystem)

  • 1 to 8 indicate specific subsystems (e.g., fuel, ignition, emissions)

• Fourth & Fifth Characters

  • These define the specific fault.

Example Code Breakdown:P0301

• P = Powertrain

• 0 = Generic

• 3 = Ignition system or misfire

• 01 = Cylinder 1 misfire detected

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🧰 Common DTC Examples

🛠️ How to Read DTCs

You can retrieve DTCs using:

• An OBD-II scanner (available at auto parts stores or online)

• Many auto parts stores offer free code reading

• Some vehicles show codes through dashboard light flashing (older OBD-I systems)

Purpose:

DTCs are used to alert the vehicle owner or mechanic about a malfunction, allowing for faster and more accurate diagnosis.

Generation:

The vehicle’s onboard diagnostic (OBD) system identifies a malfunction and generates the corresponding DTC code.

Structure:

DTCs are typically five characters long, with the first character indicating the system (e.g., P for Powertrain, C for Chassis, B for Body, U for Network). The remaining four characters specify the exact problem.

Interpretation:

Each DTC code has a specific meaning, and resources like Samsara’s guide can help decipher the code.