OBD2 Codes List & Guide: Search Your Trouble Code

What are OBD2 Codes?

All vehicles model year 1996 and newer support a selection of OBD2 codes. Diagnostic trouble codes (DTCs) may be defined by either the Society of Automotive Engineers (SAE) or the vehicle manufacturer.

Your car's on-board computer management system will store a DTC (or multiple DTCs) when it detects a problem with the vehicle. At the same time, the system usually turns on one or more dashboard warning lights.

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There are many different generic SAE-defined OBD2 codes. What's more, automakers also have manufacturer-specific codes that are defined in-house.

OBD2 codes contain a letter prefix and four numbers. A scan tool or code reader can be used to retrieve the codes, which, in turn, can be used to help troubleshoot the vehicle.

The History of OBD codes

Most automakers began fitting their cars with computer-controlled engine management systems in the 1980s. The technology uses sensors and an on-board engine management computer to minimize vehicle emissions and improve driveability. The technology eventually grew into what is now referred to as OBD2.

In 1988, the California Air Resource Board (CARB) began requiring all new vehicles sold in its state to be fitted with the first stage of OBD technology, referred to as OBD1. The agency's goal was for automotive computer management systems to continuously monitor engine-related components that could affect vehicle emissions.

CARB required that all OBD1 systems monitor emissions-related electrical components for circuit problems. If a problem were detected, the engine computer would turn on the check engine light and store a diagnostic trouble code (DTC) in its memory.

The second phase of OBD technology, OBD2, was introduced in 1996 and is still in use today. OBD2 builds on OBD1 by monitoring system functionality and being far more comprehensive overall.

OBD2 also ushered in a list of standardized DTCs that can be read with a generic scan tool or code reader. What's more, the diagnostic port for the tool to plug into was also standardized across all makes and models.

Today, OBD2 codes cover not only emissions-related powertrain and network systems, but also the chassis and body electronics.

Search OBD2 Trouble Codes Database

If you want to learn more about a specific OBD2 code, check out the CarParts.com trouble code database. Type your code into the search box and click on the article link to retrieve information.

Note: Certain codes may not be listed in the database.

List of Common OBD2 Codes

There are thousands of OBD2 codes. Here are some of the most common:

Note: The definition of the codes below may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

• P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)
  Code P0420 indicates that your car's engine computer has detected underperformance from the Bank 1 catalytic converter. A catalytic converter is an emissions control device that processes harmful exhaust gases.
• U0100 Code: Lost Communication with ECM/PCM "A"
  Modern vehicles contain dozens of control modules communicating with one another over a data network. Code U0100 is set when there's a loss of communication between the engine computer (ECM or PCM) and another module.
• P0300 Code: Random or Multiple Cylinder Misfire Detected
  A misfire results from incomplete combustion inside one of the engine's cylinders. Code P0300 indicates that your car's computer has detected an engine misfire that's random and/or appearing on multiple cylinders. You'll likely find another OBD2 code—from P0301 to P0308—alongside P0300 as these all point to engine misfires.
• P0340 Code: Camshaft Position Sensor "A" Circuit Malfunction
  Your car has one or more camshaft position sensors that calculate the speed and position of the camshaft(s) inside of the engine. The engine computer uses the data from the sensors when calculating output functions, such as fuel injection operation and ignition timing. Code P0340 indicates the PCM has detected a problem with a camshaft position sensor or its circuit.
• P0446 Code: Evaporative Emission Control System Vent Control Circuit Malfunction
  All modern cars have an evaporative emission control (EVAP) system that prevents fuel vapors from escaping into the atmosphere. Code P0446 indicates that your car's computer has detected a problem with the function of the EVAP system vent valve.
• P0430 Code: Catalyst System Efficiency Below Threshold (Bank 2)
  Code P0430 indicates that your car's engine computer has detected underperformance from the Bank 2 catalytic converter. A catalytic converter is an emissions control device that processes harmful exhaust gases.
• P0011 Code: "A" Camshaft Timing Over Advanced (Bank 1)
  Many modern vehicles have variable valve timing—a technology that alters the position angle of the camshaft(s) in relation to the crankshaft. Code P0011 indicates that the engine computer cannot correct a detected difference in the desired camshaft position and the actual camshaft position.
• P2096 Code: Post Catalyst Fuel Trim System Too Lean (Bank 1)
  The engine computer keeps track of the air-fuel mixture through oxygen sensors in the exhaust system that measure the amount of oxygen burned by the engine. There is an oxygen sensor positioned before and after the catalytic converter. If both sensors show similar data indicating a lean condition, code P2096 may be set.
• P0172 Code: Fuel System Too Rich (Bank 1)
  An engine needs the correct ratio of air to fuel to run properly. The engine computer monitors the air-fuel mixture via the oxygen sensors in the exhaust. Code P0172 indicates the computer has detected that the engine's air-fuel mixture is too rich (i.e., has too much fuel).
• U0073 Code: Control Module Communication Bus "A" Off
  U0073 is a communication system diagnostic code related to the car's data network. This code can register in a variety of modules, including the PCM, TCM, anti-lock braking system (ABS), or body control module (BCM).
• P0017 Code: Camshaft Position B – Camshaft Position Correlation (Bank 1)
  Code P0017 indicates that the engine computer detects a misalignment between the crankshaft and camshaft positions. That is, the computer believes the position of the camshaft is not where it's supposed to be in relation to the crankshaft.
• P2138 Code: Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation
  Many modern vehicles have electronic throttle control (ECT). The technology relies on input from a pair of throttle position (TP) sensors and a pair of accelerator pedal position (APP) sensors. Code P2138 is triggered when the vehicle's engine computer detects that the signals from the two throttle position sensors (or two accelerator pedal position sensors) do not correlate.
• P0141 Code: Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
  A typical oxygen sensor has a heater circuit that works to bring the sensor up to operating temperature quickly. Code P0141 indicates a problem with the heater circuit of the bank 1 downstream O2 sensor.
• P0302 Code: Cylinder 2 Misfire Detected
  A misfire results from incomplete combustion inside one of the engine's cylinders. Code P0302 indicates that your car's computer has detected an engine misfire that's occurring on cylinder two. You may find another OBD2 code—from P0301 to P0308—alongside P0302 as these all point to engine misfires.
• P0113 Code: Intake Air Temperature Sensor 1 Circuit High Input
  The intake air temperature sensor measures the temperature of the air entering the engine. Guided by this data, the computer adjusts the fuel injectors and other select components related to engine operation. Code P0113 indicates the engine computer has determined that there's a problem with the IAT sensor or its circuit.