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 out all you need to know about diagnostic error codes and how to accurately scan for them. 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 is a string of letters and numbers that’s 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.

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 into 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.

How to Read OBD2 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 OBD 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 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 to 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 code occurs when the camshaft and crankshaft aren’t operating with the correct timing. This issue often makes the engine to 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 and 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 are 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 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 into the auto repair shop. Not only will this 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.

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