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    On-Board Diagnostic Trouble Codes for Automotive Technicians Explained

    Posted by TPC Team on December 6, 2018
    TPC Team


    Remember when you didn't need a computer science degree from the Massachusetts Institute of Technology (MIT) to actively diagnose automotive issues? If something was wrong, you just tinkered with the parts.

    Sure, maybe we're over-exaggerating, but most new cars are, essentially, computers. They contain on-board diagnostic (OBD) systems that monitor the performance of major components and generate trouble codes to indicate if something has gone awry.

    Diagnostic trouble codes (DTCs) are how an OBD II interface system pinpoints and transmits issues to automotive technicians, so it’s essential that technicians be able to understand the codes to quickly identify the problem to minimize associated downtime.

    How to Read DTC Codes

    The first number in the DTC lets you know whether it’s specific to the vehicle manufacturer or an SAE generic code that applies to all OBD II systems. The last three numbers provide information regarding the specific vehicle circuit and system. See the image below for an analysis of a typical OBD II code.


    OBD II DTC Codes List

    Standard trouble codes start with P, then a four-digit numeric code. See the table below for a few common vehicle error codes and what they signify:

    DTC Codes


    Common Codes 

    Within This Range

    P0100-P0199 — Fuel and Air Metering

    These codes are used to monitor the fuel and air ratio of the vehicle's engine to determine if an oxygen sensor is failing, plus they will monitor a vehicle's emissions and fuel economy.

    • P0135: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

    • P0141: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

    • P0171: System Too Lean (Bank 1)

    • P0174: System Too Lean (Bank 2)

    P0200-P0299 — Fuel and Air Metering (Injector Circuit)

    These codes are going to involve fuel injectors.

    • P0200: Injector Circuit Malfunction

    • P0218: Transmission Over Temperature Condition

    P0300-P0399 — Ignition System or Misfire

    These codes will trigger if there are issues with the car's ignition. For example, if there are spark plug issues.

    • P0300: Random/Multiple Cylinder Misfire Detected

    • P0301: Cylinder 1 Misfire Detected

    • P0302: Cylinder 2 Misfire Detected

    • P0303: Cylinder 3 Misfire Detected

    • P0304: Cylinder 4 Misfire Detected

    • P0325: Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)

    P0400-P0499 — Auxiliary Emissions Controls

    These codes will determine issues with the system's EVAP (evaporative emission control) systems. The EVAP's function is to prevent gas fumes from reaching the atmosphere, thus keeping air pollution to a minimum.

    • P0401: Exhaust Gas Recirculation Flow Insufficient Detected

    • P0411: Secondary Air Injection System Incorrect Flow Detected

    • P0420: Catalyst System Efficiency Below Threshold (Bank 1)

    • P0430: Catalyst System Efficiency Below Threshold (Bank 2)

    • P0440: Evaporative Emission Control System Malfunction

    P0500-P0599 — Vehicle Speed Controls and Idle Control System

    These codes will monitor the vehicle's speed controls and idling. Issues from the vehicle speed sensor (VSS) will trigger these codes.

    • P0500: Vehicle Speed Sensor Malfunction

    • P0505: Idle Control System Malfunction

    P0600-P0699 — Computer Output Circuit

    These codes will be triggered by a faulty computer system.

    • P0600: Serial Communication Link Malfunction

    • P0602: Control Module Programming Error

    • P0604: Internal Control Module RAM Error

    P0700-P0899 — Transmission and Beyond

    These codes monitor the system's transmissions. Most of the time, the code is triggered by a fault in the system's transmission computer. 

    • P0700: Transmission Control System Malfunction

    • P0702: Transmission Control System Electrical 

    Download our OBD standard trouble codes list to begin troubleshooting your on-board vehicle issues.

    It's essential to have the proper tools to test and diagnose a vehicle's on-board problem.

    Accurate diagnosis is key to repair based on manufacturer suggestions. Being able to identify these OBD trouble codes will lead to decreased downtime and higher productivity.

    TPC Wire & Cable® offers a vast selection of automotive wire, cord, and automotive cable accessories, as well as an OBD interface. Let's start the conversation today about how we can reduce your downtime and costs.

    reduce downtime labor and overall cost of ownership by requesting a cost-value analysis

    Topics: Maintenance, Reducing Downtime, Products, Custom Cable, Automotive

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