OBD2 Code Lookup
Quick Answer: An OBD2 code lookup tells you what a check engine code means. Type a code like P0420 into the tool below to see its meaning, likely causes, symptoms, how urgent it is, and the typical US repair cost. Most codes point to a system, not one single part, so test before you replace anything.
Look Up a Code
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A code is one letter (P, B, C, or U) followed by four digits. It comes from your scan tool or your auto parts store printout.
Most looked-up codes:
How OBD2 Codes Work
OBD2 stands for On-Board Diagnostics, second generation. Every car and light truck sold in the United States since 1996 has an OBD2 system. The engine computer, called the ECM or PCM, watches sensors all the time. It checks fuel mixture, ignition timing, exhaust, emissions, and transmission operation. When a reading stays outside its normal range for long enough, the computer stores a diagnostic trouble code, or DTC, and turns on the check engine light.
Each code has five characters. The first character is a letter that names the system. P means powertrain, which covers the engine and transmission. B means body, which covers airbags, climate control, and lighting. C means chassis, which covers ABS, traction control, and steering. U means network, which covers communication between the car computers. Most check engine codes are P codes, and this lookup covers the most common ones.
The second character tells you if the code is generic or manufacturer-specific. A 0 means generic, so P0420 means the same thing on a Toyota, a Ford, and a Honda. A 1 means manufacturer-specific, so a P1 code can mean different things on different brands. Always check P1 codes against your exact make and model before you buy parts.
The third character names the subsystem. In P codes, 1 means fuel and air metering, 2 means fuel injectors, 3 means ignition and misfire, 4 means emissions, 5 means speed and idle control, 6 means the computer itself, and 7 means transmission. The last two digits name the specific fault inside that subsystem. So P0301 breaks down as P for powertrain, 0 for generic, 3 for ignition, and 01 for cylinder 1 misfire.
How to Use This Lookup
Start with the code from your scan tool. Type it into the box above, or tap one of the quick-pick chips for the most common codes. The result shows the full name of the code, what it means in plain English, the most likely causes, the symptoms drivers usually notice, a severity rating, and a typical US repair cost range. Use the filter buttons to browse all 49 codes by system.
Safe short-term means you can usually drive to a shop, but do not ignore the light for weeks. Repair soon means the car still runs but the fault can cause more damage or a failed emissions test if you wait. Do not drive much means the fault can damage expensive parts, such as the catalytic converter, if you keep driving. Stop driving means the car needs a tow or an immediate stop, because driving on can cause serious engine damage.
Use the likely causes as a checklist, not as a shopping list. A code never proves which part failed. P0171, for example, can come from a vacuum leak, a dirty mass airflow sensor, a weak fuel pump, or a bad oxygen sensor. A good mechanic tests the most likely and cheapest causes first.
How to Read Your Own Codes
You need a scan tool to read the codes stored in your car. The cheapest option is a basic code reader, which plugs into the OBD2 port and shows the codes on a small screen. A Bluetooth adapter costs about the same and sends the codes to a free phone app, which also shows live data such as coolant temperature and engine speed. Many auto parts stores in the US, including AutoZone and O'Reilly, will read your codes for free and print the list for you.
The OBD2 port is a 16-pin connector under the dashboard on the driver side, usually just above the pedals or behind a small trim panel. Turn the key to the on position, plug the tool in, and follow the menu to read codes. Write down every code, including pending codes.
The Most Common Codes and What They Usually Mean
P0420 and P0430 mean the catalytic converter on bank 1 or bank 2 is not cleaning the exhaust well enough. Bank 1 is the side of the engine with cylinder 1. The car often still drives normally, but it will fail an emissions test. The usual causes are a worn converter, a bad downstream oxygen sensor, or an exhaust leak. Because a converter is expensive, rule out the sensor and the exhaust leak first.
P0171 and P0174 mean the engine is running too lean on bank 1 or bank 2, which means too much air or too little fuel. P0172 and P0175 mean the opposite, too rich, or too much fuel. Lean codes often come from a vacuum leak, a dirty mass airflow sensor, or low fuel pressure. Rich codes often come from a leaking fuel injector, a bad fuel pressure regulator, or a faulty oxygen sensor. Both can cause rough running, hesitation, and poor fuel economy.
P0300 means the engine is misfiring on more than one cylinder, or the computer cannot tell which cylinder is misfiring. P0301 through P0304 name one cylinder each. Common causes are worn spark plugs, bad ignition coils, a vacuum leak, or low compression. A flashing check engine light with a misfire code is urgent, because unburned fuel can overheat and destroy the catalytic converter in minutes.
P0442, P0455, P0456, and P0457 are EVAP codes, which means the system that traps fuel vapor has a leak. P0457 is often just a loose gas cap, so tighten the cap until it clicks and drive for a few days. These codes rarely affect how the car drives, but they will fail an emissions test.
P0700 means the transmission control module has stored a fault. It does not tell you what the fault is, so a scan tool that can read transmission codes is needed to see the real code behind it. Transmission codes deserve a specialist, because guessing wrong can cost thousands of dollars.
When Is It Safe to Drive?
A steady check engine light with no other symptoms is usually safe for a short trip to a shop. Check the oil level and the coolant level first, and listen for new noises. If the engine runs smoothly, the temperature gauge is normal, and no other warning light is on, drive gently and get the code read soon. Do not take a long road trip with the light on until you know the code.
A flashing check engine light is different. It means an active misfire that is sending unburned fuel into the exhaust. Slow down, avoid hard acceleration, and get to a shop right away. Driving on can turn a spark plug job into a catalytic converter replacement.
Stop driving at once if the oil pressure light is on, the temperature gauge is in the red, you smell fuel strongly, or you see smoke. Get the car off the road first.
Browse All Codes
Use the search box above or the filters below to find a code. Tap any row to see its full result.
| Code | Meaning | Severity | Typical US Cost |
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Costs are typical US ranges for parts and labor at an independent shop in 2026, not quotes. Dealer prices and prices in high-cost cities can be higher. Always get a written estimate before authorizing a repair.
Frequently Asked Questions
What does an OBD2 code mean?
An OBD2 code, also called a diagnostic trouble code, is a five-character code your car computer stores when it finds a fault. The first letter shows the system, P for powertrain, B for body, C for chassis, and U for network. The rest of the code narrows the fault down to one sensor, part, or circuit.
How do I read my own OBD2 codes?
Plug a scan tool or a Bluetooth OBD2 adapter into the 16-pin port under the dashboard on the driver side, then read the codes from the tool or its phone app. Every car sold in the US since 1996 has this port. Many auto parts stores will also read your codes for free.
What is the most common OBD2 code?
P0420, catalyst system efficiency below threshold on bank 1, is one of the most common codes in the US. P0171, system too lean on bank 1, and P0300, random misfire, are also very common. All three can have more than one cause, so the code alone does not name the failed part.
Can I drive with the check engine light on?
It depends on the code. A steady light with a code like P0455, a large EVAP leak, is usually safe for a short trip. A flashing check engine light means an active misfire that can damage the catalytic converter, so slow down and get it checked right away. If the car runs rough, overheats, or loses power, do not keep driving.
What is the difference between a generic and a manufacturer-specific code?
Generic codes start with P0, B0, C0, or U0 and mean the same thing on every car. Manufacturer-specific codes start with P1, B1, C1, or U1 and mean different things by brand. A P1 code on a Nissan can mean something completely different from the same P1 code on a Ford.
What is a pending OBD2 code?
A pending code means the computer saw a fault once but it has not happened enough times to turn on the check engine light. If the fault repeats on later drives, the pending code becomes a confirmed code and the light comes on. Pending codes help catch a developing problem early.
Will clearing the code fix the problem?
No. Clearing a code only erases the stored fault and turns the light off. If the fault is still there, the code will come back, usually within a few drives. Clearing also erases the readiness monitors, which can cause a failed emissions test until the car completes a full drive cycle.
How much does it cost to fix a check engine light code?
It depends on the code. A loose gas cap can cost nothing. An oxygen sensor repair often costs $200 to $400. A catalytic converter replacement often costs $1,000 to $2,500. The code points to a system, not a part, so a shop should test before replacing anything. Costs on this page are typical US ranges, not quotes.
Reviewed by the AutoFixr Editorial Team. Code meanings follow the SAE J2012 standard for generic OBD2 codes. Repair costs are typical US ranges, not quotes. Always confirm a diagnosis with a qualified mechanic before replacing parts.