Check engine code lookup

Enter any OBD-II diagnostic trouble code to get the full explanation, urgency rating, likely causes, and repair cost ranges. Works for P, B, C, and U codes. Free — no sign-up required.

What is an OBD-II code?

OBD-II (On-Board Diagnostics, second generation) is a standardized diagnostic system required in all vehicles sold in the United States after January 1, 1996. When your vehicle's engine control unit (ECU) detects a fault it cannot correct, it stores a five-character Diagnostic Trouble Code (DTC) and illuminates the check engine light on your dashboard.

Before OBD-II was standardized, each manufacturer used their own proprietary diagnostic systems with different connectors, different protocols, and different code formats. OBD-II replaced all of that with a single universal standard — which is why any OBD-II scanner works on any vehicle from 1996 onward, regardless of make or model, and why P0420 means the same thing on a Toyota as it does on a Ford.

The four OBD-II code categories

Every OBD-II code begins with a letter that identifies the vehicle system where the fault occurred:

• P
  Powertrain

  Engine, transmission, fuel system, ignition, emissions. The most common category — P codes account for roughly 80% of all check engine light faults.
• B
  Body

  Airbags and SRS restraint systems, HVAC, power windows, power seats, and other body electronics.
• C
  Chassis

  ABS (anti-lock brakes), traction control, electronic stability control, power steering, and suspension systems.
• U
  Network

  CAN bus communication between control modules. U codes indicate modules have lost communication with each other.

How to read a 5-character OBD code

Take the code P0420 as an example. The first character (P) tells you it's a powertrain code. The second character (0) means it's a generic SAE-standard code — codes starting with 0 are universal across all manufacturers. A 1 in the second position means it's a manufacturer-specific code. The remaining three digits (420) identify the specific fault within that system.

This structure means you can often narrow down what a code refers to just from the number range — P02xx codes are typically fuel and air metering faults, P03xx are ignition system faults, P04xx are auxiliary emissions control faults, and so on.

Steady check engine light vs. flashing check engine light

Not all check engine lights are equal. A steady (solid) light means a fault has been stored and logged. The car is generally safe to drive to a shop. Schedule a diagnostic appointment within a few days.

A flashing or blinking light is a completely different situation — it means an active engine misfire is occurring right now. Raw, unburned fuel is entering your catalytic converter and burning inside it at temperatures it was never designed to handle. This can destroy a catalytic converter (a $400–$2,200 part) within minutes of driving. If your check engine light is flashing, pull over safely and stop driving. Do not drive to a shop — arrange a tow.

How to get your OBD code

You need an OBD-II scanner to read the stored code from your vehicle. There are three options, ranging from free to inexpensive:

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  Auto parts store (free): AutoZone, O'Reilly Auto Parts, and Advance Auto Parts will read your OBD codes free in-store. Walk in, ask them to scan it, and they hand you a printout with the code. Takes about 5 minutes.
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  Bluetooth OBD adapter ($15–$30): A Bluetooth or WiFi OBD-II adapter plugs into your OBD port (under the dashboard, driver's side). Pair it with a free app like Car Scanner ELM OBD2 or Torque Lite and read the code on your phone. Works on any vehicle from 1996 onward.
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  Handheld scanner ($35–$120): A dedicated handheld scanner like the Foxwell NT301 reads and clears codes without a smartphone. Good if you want a standalone tool that also checks emissions readiness monitors.

Once you have the code, enter it in the lookup tool above. MyOBDCode gives you the meaning, the most likely causes ranked by frequency, the urgency level, and realistic repair cost ranges — everything you need before calling any shop.

Why reading the code before calling a mechanic saves money

Automotive repair is an industry built on information asymmetry. A mechanic who knows you have no idea what's wrong has every incentive to recommend expensive repairs. A car owner who walks in saying "I have a P0171 — I know it could be a vacuum leak, dirty MAF sensor, or fuel pump issue — what does your diagnosis show?" is an entirely different conversation.

Knowing your code also helps you identify when a shop is recommending an unnecessary repair. A P0442 (small EVAP leak) can often be fixed with a $10 gas cap. A shop that quotes you $400 for EVAP system repairs without first checking the gas cap is a shop to be suspicious of. The repair cost ranges on every MyOBDCode page give you a benchmark for what any repair should realistically cost.

Frequently asked questions