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What is my check engine light telling me?
Enter your OBD2 code below and we will explain it in plain English — then help you get real quotes from local autoshops.
Free tool
OBD2 code lookup
Type the five-character code from your scanner, for example P0420 or P0171.
Do not have a code yet? Many auto parts stores will read it for free — see the steps below.
What is an OBD2 code?
An OBD2 code is a standardized diagnostic trouble code that your car's computer stores when it detects a problem. Every vehicle sold in the United States from 1996 onward uses the same system, so the same code means the same thing whether you drive a Honda, a Ford, or a BMW. The code is five characters long — a letter followed by four digits, such as P0420 — and it identifies the system reporting the fault.
Your check engine light is the dashboard warning tied to that stored code. The light tells you something was detected; the code tells you where to look.
Step by step
How to read your OBD2 code
It takes about five minutes and you do not need to be a mechanic.
Find the port
Look under the dashboard on the driver's side, near the steering column. You are looking for a trapezoid-shaped connector, standard on any car from 1996 onward.
Plug in a scanner
Connect an OBD2 scanner to that port. If you do not own one, many auto parts stores such as AutoZone and O'Reilly Auto Parts will read the code for you at no charge.
Read it and look it up
Turn the key to on without starting the engine, then note the five-character code exactly. Enter it above to see what it means and what it usually takes to fix.
Most looked-up
Common check engine light codes
A few of the codes drivers ask about most, and what they usually point to.
P0420
Catalyst efficiency below threshold. Often a failing catalytic converter, but an oxygen sensor, exhaust leak, or misfire can trigger it too — worth confirming before replacing anything. Read the full P0420 guide.
P0171
System too lean, bank 1. The engine is getting more air than fuel. Common causes are a vacuum leak, a dirty mass airflow sensor, or a weak fuel pump.
P0300
Random or multiple cylinder misfire. Often spark plugs, coils, or fuel delivery. If the light is flashing, stop driving and get it looked at promptly.
P0455
Large evaporative emissions leak. The classic first suspect is a loose or cracked gas cap — one of the cheapest fixes on this list.
P0128
Coolant temperature below thermostat regulating temperature. Usually a thermostat stuck open, which also hurts your fuel economy and cabin heat.
P0442
Small evaporative emissions leak. A small leak in the fuel vapor system — again, often the gas cap or a hose, but a shop can smoke-test to confirm.
Straight answers
Check engine light questions
Can I still drive with the check engine light on?
A steady light usually means you can drive short distances but should get it looked at soon. A flashing light means a serious misfire that can damage your catalytic converter — pull over safely and have the car checked right away.
What does the letter at the start of the code mean?
It identifies the system. P is powertrain (engine and transmission), B is body (airbags, seatbelts), C is chassis (brakes, suspension), and U is network (modules talking to each other).
Where can I get my code read for free?
Many auto parts retailers, including AutoZone and O'Reilly Auto Parts, will read it at no cost. You can also buy a basic scanner, or have a local autoshop pull it as part of a diagnostic.
Does clearing the code fix the problem?
No. Clearing it only erases the stored record and turns the light off for a while. If the fault is still there, the code and the light come back — the underlying cause has to be repaired.
Does the code tell me exactly which part to replace?
Not always. A code names the system reporting a problem, not always the failed part. P0420, for instance, reports catalyst efficiency below threshold — that can be the catalytic converter, but it can also be an oxygen sensor, an exhaust leak, or a misfire upstream. A good shop confirms the cause before replacing expensive parts.
How much will the repair cost?
It depends entirely on the cause — a gas cap is a few dollars, a catalytic converter is one of the pricier jobs on a car. The quickest way to find out for your vehicle is to send a service request with your code and let local autoshops reply with real pricing.
Know the code. Now get a real price.
Send your code to local autoshops and see what the repair actually costs near you.