Diagnostics · Free tool
Free OBD2 Code Lookup
Enter the code your scanner shows. You get its meaning in plain English, the usual causes and whether you can keep driving.
- Free to use
- No signup
- Runs in your browser
Your result
Enter a code to decode it.
You will get what the code means, the usual causes and whether it is safe to keep driving.
A code names the circuit or system that reported a fault. It does not name the part that failed.
General information about the code, not a diagnosis of your car. Read the disclaimer. Updated .
02Your result
What your OBD2 code result means
A code is the car’s own note about what it noticed. It tells you where to look, not what to replace.
- 01
The definition
The standard meaning of the code. Generic codes are defined by an industry standard, so they read the same on every make.
- 02
The common causes
The faults that most often set that code, cheapest and likeliest first. Check them in that order.
- 03
Whether to keep driving
How urgent the fault is. A flashing check engine light always overrides this: stop driving.
What to do next
Decide whether it is safe to drive
Answer three questions about the light and the car’s behavior.
Check engine light checkerPrice the repair
Build an estimate from parts and labor, and compare it with the national average.
Repair cost estimatorBrowse every code
A searchable table of 314 common generic codes with their descriptions.
Full code table
03How it works
How an OBD2 code is structured
There is no arithmetic here. Every code is five characters, and each position has a job.
P = powertrain. 0 = generic (SAE) code. 4 = auxiliary emission controls. 20 = the specific fault
Together: catalyst system efficiency below threshold, bank 1.
What each term means
- 1st: letter
- The system. P is powertrain, B is body, C is chassis and U is the network that links the car’s computers.
- 2nd: 0 or 1
- 0 is a generic code with a standard meaning. 1 is manufacturer-specific, so its meaning depends on the make.
- 3rd: digit
- The sub-system. On powertrain codes, 1 and 2 are fuel and air metering, 3 is ignition or misfire, 4 is auxiliary emission controls and 7 is transmission.
- 4th and 5th
- The specific fault within that sub-system.
What the tool assumes
- Detailed entries cover the codes drivers meet most often.
- Standard definitions are held for 314 common generic codes, following SAE J2012.
- For any other valid code, the tool explains what its structure tells you.
- Manufacturer-specific codes (second character 1) need your make’s own service information.
04Worked example
OBD2 code example: reading P0420
The code behind the most common check engine light repair, taken apart one character at a time.
- 01
First character: P
The fault is in the powertrain: engine, transmission or emissions
Powertrain
- 02
Second character: 0
A generic code, defined by the SAE standard
Generic
- 03
Third character: 4
The sub-system involved
Emission controls
- 04
Last two: 20
The specific fault
Catalyst efficiency
- 05
Put together
Catalyst System Efficiency Below Threshold (Bank 1)
P0420
What P0420 tells you
P0420
The sensor after the catalytic converter reports that the converter on bank 1 is not cleaning the exhaust well enough. That can be the converter, or a cheaper fault such as an oxygen sensor or an exhaust leak.
Try your own numbers05Background
How OBD2 trouble codes work
OBD2 is the diagnostic system built into every modern car. It has been required on gasoline cars and light trucks sold in the United States since the 1996 model year. When the engine computer sees a reading outside its normal range, it stores a diagnostic trouble code and, for emissions faults, turns on the check engine light.
| Letter | System | Examples |
|---|---|---|
| P | Powertrain: engine, transmission and emissions | P0300 misfire, P0420 catalyst efficiency |
| B | Body: airbags, seats, climate and comfort | Airbag and seat belt circuit faults |
| C | Chassis: brakes, steering and suspension | ABS wheel speed sensor faults |
| U | Network: communication between computers | U0100 lost communication with the engine computer |
The definitions of the generic codes come from one industry standard, SAE J2012. That is why a P0420 means the same thing on a Ford as on a Toyota, and why one inexpensive scanner works on every car.
A code is a starting point. It names the circuit or system that reported a fault, and several different parts can cause the same one. See the first steps in the OBD2 guide for how to read a code and what to do next.
06When to use it
When to use an OBD2 code lookup
Any time a scanner hands you five characters and no explanation.
When the check engine light comes on
Read the code and find out what it means before you call anyone.
After a free parts-store scan
Check the code they give you against an independent explanation.
Before approving a repair
See the usual causes, so you can ask whether the cheaper ones were ruled out.
When inspecting a used car
Scan it for stored codes and look up anything you find.
Mistakes to avoid.
- Replacing the part a code seems to name before checking the cheaper causes.
- Clearing the code to make the light go away. The fault is still there and the light will return.
- Ignoring a flashing check engine light because the car still moves.
- Assuming a manufacturer-specific code means the same thing on a different make.
07Related guides and tools
Keep going from here.
Guides that go with this tool
- Best OBD2 Scanners: From $20 Readers to Pro-Grade Tools
- P0420 Code: Catalyst System Efficiency Below Threshold - Causes & Fixes
- How to Read OBD2 Codes: Step-by-Step Guide
- OBD2 Code Structure Explained: What Each Character Means
- What Is OBD2? How On-Board Diagnostics Works
- Most Common OBD2 Codes (Data From Our Lookup Tool)
- How to Clear Check Engine Light Codes (and When Not To)
Related tools
- Check Engine Light CheckerSteady or flashing? Find out whether it is safe to keep driving and what to do next.
- Repair Cost EstimatorBuild a repair estimate from parts, labor hours and shop rate, and compare it with national averages.
- Car Symptom Diagnosis ToolPick what the car is doing and see the common causes and what to check first.
08Questions
OBD2 Code Lookup: your questions.
How do I look up an OBD2 code?
Plug a scanner into the OBD2 port under the dashboard, note the five-character code and enter it in the lookup above. You get the meaning, the common causes and whether it is safe to keep driving.
What do the letters in an OBD2 code mean?
The first letter is the system: P for powertrain, B for body, C for chassis and U for the network between the car’s computers.
What is the difference between a P0 and a P1 code?
A P0 code is generic. It has a standard meaning that is the same on every make. A P1 code is manufacturer-specific, so its meaning depends on who built the car.
Can I read OBD2 codes without a scanner?
On most cars, no. You need a scanner or code reader. Many auto parts retailers will read the code for free.
Does clearing a code fix the problem?
No. Clearing a code only erases the record and switches the light off. If the fault is still present, the car will detect it again and the light will come back.
09Estimates and sources
Read this before you rely on it.
Built and checked by CarTipsMentor Team. Last updated . How we check our work.
Sources
- [1]SAE International, J2012: Diagnostic Trouble Code Definitions
- [2]California Air Resources Board, On-Board Diagnostic II (OBD II) Systems Fact Sheet
- [3]Innova, Diagnostic Trouble Codes (DTCs)
- [4]Haynes, What Are Diagnostic Trouble Codes?
- [5]CarMD, 2026 Vehicle Health Index (calendar-year 2025 repair data)