Number OBD2 Code Lookup
Type any generic trouble code — P0420, P0300, C0035 — or search by keyword ("catalyst", "misfire cylinder 2"). All 9,533 standardized generic codes are in the database, with causes, severity and what to check first. The 150 most common codes also carry a full guide.
Fast examples: P0420 · P0300 · P0171 · P0455 · C0035 · U0100. The database loads once (about 7 MB) and every search after that is instant — and nothing about your car ever leaves your browser.
How it works
Since 1996, every car sold in the US reports faults in one language: a letter (P powertrain, C chassis, B body, U network) plus four digits. The definitions are standardized facts; the plain-English explanations here are written independently — the underlying SAE J2012 document is copyrighted and is not reproduced. Our dataset covers all 9,533 generic codes from OBDex, an open dataset of independently authored code descriptions released under CC0 (public domain), fetched once at build time and served as a static file from this site — there are no live third-party calls when you search. The model is deliberate: the lookup answers every code; a dedicated guide page is earned by frequency. The 150 most common codes — selected from the repair-frequency data published in the CarMD Vehicle Health Index — carry full guides with misdiagnosis traps, DIY-vs-shop splits and warranty notes. Severity shown here is our editorial triage, printed so you can see the rule: flashing-light misfires (P030x) are stop-soon, limp-mode/transmission/ABS faults are fix-promptly, emissions faults that drive normally are plan-the-repair.
Method & worked example
Method: Type or speak the code exactly as the scanner shows it (a letter plus four digits), or search the 9,533-code dataset by keyword; exact matches rank first, then code prefixes, then title keywords. Severity follows the printed triage rules — misfires stop-soon, limp-mode/transmission/ABS faults fix-promptly, emissions faults plan-the-repair.
Worked example: Searching "P0171" returns System Too Lean Bank 1 with its ranked causes led by intake/vacuum leaks and MAF faults — and because P0171 is a top-150 code, the result links straight to its full guide with misdiagnosis traps and DIY-vs-shop costs.
When to use this
- The check-engine light came on and a parts-store scan (or your own scanner) gave you a code
- A shop quoted a repair from a code and you want the second opinion before paying
- You are triaging: is this a drive-it-home code or a tow-it code?
- You bought a used car and want to understand its stored history codes
How to use it, step by step
- Read ALL stored codes, not just the first — write them down in order.
- Type the first code exactly (letter + four digits), or search by the symptom keyword.
- Read the severity line first: stop-soon, fix-promptly, or plan-the-repair.
- Work the causes in ranked order — cheapest and most likely first.
- If your code is in the top 150, open its full guide for traps, diagnostic steps and costs.
- Price the likely fix in the Repair Cost Estimator before authorizing anything.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Code or keyword | A generic OBD-II code (P/C/B/U + four digits) or plain words from the code's title | P0420 · catalyst · misfire cylinder 2 · C0035 |
| The dataset | All 9,533 generic codes from OBDex (CC0), loaded once into your browser — searches are local and instant | Manufacturer-specific codes (P1xxx…) are not generic and are not included |
Another worked example
A driver with a flashing light searches "P0300" and gets Random/Multiple Cylinder Misfire with stop-soon severity: the safe move is a gentle drive or a tow, because the misfire is dumping fuel into a catalytic converter that a $480 coil-and-plug job (CarMD's published average) protects — while the converter itself averages $1,511.
Frequently asked questions
My scanner shows a code that is not in the lookup. Why?
It is probably a manufacturer-specific code. Generic (SAE-standardized) codes are the shared language this database covers; codes in the P1xxx/P3xxx ranges and much of the B/C/U 1xxx space are defined by each manufacturer, and the same number can mean different things on different brands. Your brand's service information is the authority for those.
Can I clear the code and see whether it comes back?
You can — and after a real fix (say, a loose gas cap resealed), clearing is exactly right. But clearing before diagnosis erases the freeze-frame data (the conditions when the fault set) that helps a technician, and resets the readiness monitors, which fails an emissions inspection until they re-run. Diagnose first, clear last.
The light went off by itself. Am I done?
For intermittent faults the light can go out after several clean trips while the code stays stored as history. The underlying fault — a chafing wire, a drifting sensor — usually returns. A stored history code is worth mentioning at the next service even with the light off.
Why does one code have so many possible causes?
Because a code reports a test the car failed, not a broken part. P0420 says "the converter is not cleaning as expected" — the cause can be the converter, its sensors, an exhaust leak, or an engine fault poisoning it. Ranked cause lists, and the full guides, exist to order the testing so cheap, likely causes are checked before the expensive part is replaced.
Is a $25 Bluetooth scanner enough?
For reading and clearing generic powertrain codes and watching live fuel trims and misfire counters — the data that drives most diagnoses on this site — yes. ABS, transmission, airbag and body codes on many brands need a scanner that can talk to those modules; that is the honest limit of the cheap tools.
🔧 Know the code — now price the fix
The Repair Cost Estimator turns the likely causes into parts and labor ranges for your state and vehicle class.
What is the difference between generic and manufacturer codes?
Generic codes are defined by the SAE standard and mean the same thing on every brand — that is the set of 9,533 in this lookup. Manufacturers additionally define their own codes (mostly in the 1xxx ranges) whose meanings vary by brand and sometimes by model year; those need the manufacturer's own documentation.
Why do parts stores scan for free but shops charge for diagnosis?
Reading a code takes two minutes; diagnosis is the testing that follows — live data, electrical checks, smoke machines — to find WHICH cause on the list is yours. The code is the question, not the answer, and the diagnosis fee pays for the answer.