OBD2 Codes: Definition, Common Codes & How To Scan for Them

Knowing how to accurately read OBD2 error codes is an extremely useful skill for any mechanic or DIY enthusiast. Error (or trouble) codes are alerts sent out by a car’s OBD2 system to indicate automotive issues via a check engine light or another alert like an issue with your antilock braking system (ABS). Using an OBD2 scanner, users can view these codes and understand any problems with their car.

An OBD2 (or OBDII) scanner is a powerful car diagnostic tool that is widely used in professional auto repair shops. Aside from reading trouble codes, an OBD2 scanner can turn off check engine and oil lights, display real-time vehicle data and sometimes even recode some vehicle functions.

In this guide, you’ll find all you need to know about diagnostic error codes and how to scan for them accurately. We’ll also explain how to use our helpful car code chart to work out exactly what your error alerts mean.

What Is an OBD2 Code?

An OBD2 code, also referred to as DTC (Diagnostic Trouble Code), is a string of letters and numbers that are produced by a vehicle’s computer when it detects a problem within its systems. OBD2 fault codes can indicate issues with the transmission, engine, fuel system, and much more.

OBD stands for “On-Board Diagnostics” and is a system that is built into all modern vehicles. OBD2 is the latest iteration of this system and has been required by law for all cars manufactured in the US since 1996. OBD2 scanners are tools that tap into this system to give diagnostic information to the user. If you want to scan cars built before 1996, then you’ll need an OBD1-compliant scanner.

Most OBD2 scanners will let you know which error codes it has detected, but some will actually give you a short description of what they mean. Even if your scan tool doesn’t give a description, you can easily look up what your car diagnostic trouble codes mean online.

Where Do DTCs Come From?

DTCs are generated by the vehicle’s OBD system whenever it detects a fault. The OBD system diagnoses the issue and displays the DTC through visual warnings, such as the illumination of a check engine light. This allows external devices, for example, and OBD scanner, to interact with a vehicle’s onboard computer system to diagnose the errors.

There were many different versions of OBD interfaces used, which were classified as OBD1 and varied significantly across manufacturers. These days, there are two main types of interfaces that we can use to read DTCs. These interfaces are:

  • OBD2 – best for light- and medium-duty vehicles
  • J1939 – best for heavy-duty vehicles

With the introduction of OBD II, the Society of Automotive Engineers (SAE) created a standard DTC codes list which contains codes that are common to all manufacturers.

Although the OBD II system is widely used, it’s crucial to note that manufacturer-specific DTCs still exist and may come across them. In some cases, manufacturers may create their individual DTCs as supplements to the list of universal codes as long as the vehicle requires it. Still, those manufacturer-specific codes are often difficult to interpret, and support from a professional mechanic is needed.

What OBD2 Codes Tell You

Car diagnostic codes can indicate a wide range of vehicle problems. Here’s a small selection of the potential car issues that can produce a diagnostic trouble code (DTC):

  • Cylinder misfires
  • Vehicle speed sensor errors
  • Transmission control system issues
  • Airbag and seatbelt malfunctions
  • Intake air temperature sensor errors
  • Incorrect fuel mixing ratios
  • Exhaust system failures
  • General engine problems

OBD2 codes are standardized across vehicle manufacturers, meaning the same error code is always produced for a particular problem. This makes it fairly straightforward to read error codes and diagnose vehicle issues.

For example, if your OBD2 scanner points to a code error involving your EVAP system, you can do basic troubleshooting like checking for a loose gas cap or small leaks.

This is great for the home mechanic, who can work out what the problem is with their car without having to take it to an auto repair shop. They can even attempt the repairs themselves if they’re confident. Having a car code reader can help vehicle owners save a load of time and money.

Car Diagnostic Codes List

CodeMore info
P0175Read more about P0175 code
P0332Read more about P0332 code
P0500Read more about P0500 code
P0420Read more about P0420 code
P0122Read more about P0122 code
P06DDRead more about P06DD code
P0335Read more about P0335 code
P059FRead more about P059F code
P1450Read more about P1450 code
P219ARead more about P219A code
P0496Read more about P0496 code
P1778Read more about P1778 code
P1326Read more about P1326 code
U11E9Read more about U11E9 code

How to Read OBD2 Scan Codes

– The chart should look something like this:

Character Placement


First Character – Letter

Notes what part of the vehicle has an error. 

P – Powertrain. Includes engine, transmission and related accessories

B – Network & vehicle integration. Includes functions managed by the vehicle’s onboard computer system

B – Body. Includes parts found in the passenger compartment area.

C – Chassis. Includes mechanical systems like breaks, steering and suspension.  

Second Character – Number

Notes whether the code is generic or manufacturer specific 

0, 2 or 3 – Tells you the code is a generic code or standardized code (SAE). 

1 – Tells you that the code is a manufacturer-specific code.

Third Character – Number/Letter

Notes what system in the vehicle has an error. 

0 – Fuel and air metering & auxiliary emissions control 

1 – Fuel and air metering 

2 – Fuel and air metering (Injector circuit) 

3 – Ignition systems and misfires

4 – Auxiliary emissions control

5 – Vehicle speed control and idle control systems

6 – Computer and output circuit 

7 – Transmission

Letters A-F – Hybrid trouble codes

Fourth & Fifth Characters – Number

A two-digit number that tells you exactly what problem you’re dealing with. These can range anywhere from 00-99.

Most Common OBD Codes

There are some OBDII scanner codes that come up more often than others. Knowing about these common codes is an easy way to speed up your problem diagnosis and repairs.

P0171 or P0174 – System Too Lean

Both of these DTC codes mean that your fuel mix is too lean (too much air compared to fuel). P0171 refers to the sensor on one side of the exhaust system and P0174 on the other. Be sure to double-check if your OBD2 tool detects one of these codes – they can sometimes be false readings.

P0010 – Camshaft Position Actuator Circuit Malfunction

This OBD2 scanner code occurs when the camshaft and crankshaft aren’t operating with the correct timing. This issue often makes the engine run with a high RPM. Possible causes include poor engine oil, wiring damage, crankshaft damage, or out-of-sync ECM timing.

P0135 or P0141 – O2 Sensor Circuit Malfunction

Your scan tool will display a P0135 or P0141 error code when a problem with an oxygen sensor has been detected. The vehicle’s computer uses these sensors to check that the right amount of oxygen is being drawn into the engine, so it’s important that they’re functioning correctly.

P0200 – Injector Circuit Malfunction

An injector circuit malfunction is detected when either the voltage or resistance of the fuel injection sensor is out of range. This means that the sensor cannot accurately measure the amount of fuel being sent to the engine, which could lead to further problems.

P030(1-4) – Cylinder Misfire Detected

A P030X code lets you know that one of the cylinders has misfired. For example, if you read a P0303 error code, then it means cylinder 3 has an issue. Cylinder misfires are typically caused by worn-out spark plugs or a faulty ignition coil.

P0401 – Insufficient EGR Flow Detected

Insufficient EGR (exhaust gas recirculation) flow means that there’s not enough exhaust gas coming into the engine via the EGR valve. Exhaust gas recirculation is a system used to limit emissions by reusing air in the engine.

P0500 – Vehicle Speed Sensor Malfunction

A P0500 code is another common alert that indicates that the computer is not receiving an accurate signal from the car’s speed detection sensors. Of course, this is a serious problem and requires immediate investigation.

P0602 – Control Module Programming Error

This code is displayed when there’s a programming error inside one of the vehicle’s control modules. These errors often lead to problems such as rough engine idling, regular stalling and lack of acceleration.

P0700 – Transmission Control System Malfunction

P0700 is a generic trouble code that means there’s a problem with the system that controls your automatic transmission. There is a range of issues that could cause this malfunction, including faulty wiring, old transmission fluid, and a deteriorated valve body.

Does My Car Have OBD2?

Vehicle manufacturers have been using OBD2 in their cars for over 20 years. In fact, OBD2 systems are mandated by law for all cars and light trucks manufactured after 1996. If your car was built before 1996, then it will have the earlier OBD1 system and will require a special OBD1 code reader.

All of the leading brands including Chrysler, Honda, Toyota, Ford, and Chevrolet consistently use reliable OBD2 systems across their vehicle ranges. The move towards OBD2 has been a huge benefit for vehicle owners and mechanics, who can now diagnose vehicle problems in a matter of seconds.

Most OBD2 scanner codes are the same across different vehicle brands, but there’s also a range of manufacturer-specific codes to know about too. In general, manufacturer-specific codes will start with P1, whereas generic codes will start with P0, P2, or P3. For example, in Ford vehicles, the P1700 code indicates transmission problems.

Using an OBD2 Scanner at Home

OBD2 scanners are absolutely ideal for home use. All you need is a simple scan tool and a data link connector (DLC) to get started. Although they can seem hard to understand at first, OBD2 tools are actually quite intuitive and easy to get the hang of.

To make your diagnosis sessions even more straightforward, you might consider looking for code readers that come with a Bluetooth connector. You can even find a Bluetooth adapter that connects up to a diagnostic app on your smartphone. This solution is perfect for the amateur mechanic who doesn’t require a full-blown professional tool for their vehicle.

Using an OBD2 scanner at home provides a number of benefits. Most importantly, you can clear unnecessary DTC codes without having to take your vehicle to the auto repair shop. If you’re using a scan tool, you may need to enter any vehicle-specific information requested. You may also be asked to provide the Vehicle Identification Number (VIN).

Using an OBD2 scanner at home will not only save you money in the long run, but it will save your valuable time too.

Learning More About OBD2 Codes and Scanners with OBD Station

We hope that this article has answered all of your OBD2 code questions. If you still want to learn more, then be sure to head over to the OBD Station blog. You can find reliable OBD2 scan tool reviews, regular industry updates and useful tips for keeping your vehicles running smoothly.

OBD Codes FAQs

How to search for an OBD code?

In order to do a diagnostic code lookup, you must first establish whether your code is generic or manufacturer-specific.

If your code is generic (common for different manufacturers), you don’t have to include your car brand, as these codes are standardized and have the same meaning for any car manufacturer.

However, if your code is manufacturer-specific, your search term should include both the code and your car brand to find suitable criteria.

Is my vehicle OBD II or J1939 compliant?

Vehicles considered OBD II compliant include cars and light trucks built and sold in the United States after January 1, 1996. Those vehicles were required to be equipped with an OBD II system.

Most heavy-duty vehicles and buses are considered the industry standard for J1939. Also, most diesel engines manufactured vehicles are J1939 compliant.

If you’re not sure whether your vehicle is compatible with OBD II or J1939, it’s best to check your vehicle manual, do online research or consult with your dealership.

How do I set up an OBD2 scanner for my car?

The process of setting up your OBD2 scanner depends on the brand and model of your vehicle. When you buy a new scanner, you must go through a one-time setup process in order to have your scanner custom-tuned to your car’s specifications.

The first step you must take is to download the required software on your computer or smartphone. If you’re connecting with the scanner through a computer, you may also need to link via wireless Bluetooth.

In order to connect your scanner to your car, you must plug the device into a 16-pin connection point, which is typically located on the driver’s side underneath the dashboard. As OBD pins are designed to fit various areas throughout the vehicle, each pin on this connection point has its individual source of power.

Once you have the required software installed, navigate through a menu with a tool, smartphone, or computer. If you’re using a standalone tool, there are specific buttons to navigate, such as arrow keys.

As long as the OBD2 scanner is compatible with your vehicle, you will be able to scan your car for any problems and work with these code components throughout it.

How can I manually do an engine code lookup?

If you want to do an engine code lookup by yourself, you can do so by flipping your vehicle’s ignition on and off a few times without cranking the engine and finishing with the key in the on position. Your vehicle will then check for any saved error codes.

You should notice all the lights light up on the dash until only one remains on, which is usually the “service engine” light.