What Is an Engine Light Checker?

An engine light checker is any tool or device that reads the diagnostic trouble codes (DTCs) stored in your vehicle's computer when the check engine light comes on. These range from $15 handheld scanners to smartphone-based solutions like Steer.

The good news: you don't need to be a mechanic to use one. And you definitely don't need to spend $100+ at a shop just to find out why your light is on.

Ways to Check Your Engine Light

Method	Cost	Ease	What You Get
OBD-II Bluetooth Scanner + App	$20 – $60 (one-time)	Easy	Code + basic description
Steer System	Hardware + subscription	Easiest	Code + plain-English diagnosis + severity + action plan
AutoZone / O'Reilly (free scan)	Free	Medium	Code number only (no interpretation)
Professional Mechanic	$80 – $150	Easiest	Full diagnosis but expensive
Handheld Code Reader	$15 – $40	Easy	Code + generic description

How to diagnose Engine Light Checker: How to Check Your Engine Light for Free — OBD2 car scanner guide — Engine Light Checker: How to Check Your Engine Light for Free — Diagnostics diagnostic guide

How to Check Your Engine Light at Home

Step 1: Get an OBD-II Scanner

You need an OBD-II scanner or a Bluetooth dongle that pairs with your phone. Every car made after 1996 has a standard OBD-II port, usually under the dashboard on the driver's side.

Step 2: Plug It In

With the engine off, plug the scanner into the OBD-II port. Turn the ignition to "On" (don't start the engine) or start the car.

Step 3: Read the Code

Use the scanner or app to pull stored DTCs. You'll get codes like P0171, P0420, P0300, etc.

Step 4: Understand What the Code Means

This is where most free tools fall short. They show you "P0171 — System Too Lean" but don't tell you:

What caused it (vacuum leak? dirty MAF sensor? weak fuel pump?)

How serious it is (safe to drive? or stop immediately?)

What to do next (DIY fix? or mechanic required?)

Where to Get a Free Check Engine Light Scan

Store	Free Scan?	Details
AutoZone	✅ Yes	Read and print codes, available in-store
O'Reilly Auto Parts	✅ Yes	Free code reading at the counter
Advance Auto Parts	✅ Yes	Code scan with code lookup assistance
Walmart Auto Center	❌ No	Does not offer free scans
Dealership	❌ No	Typically charges $100 – $150

Important: Free scans at auto parts stores only give you the code number. They don't diagnose the root cause or tell you the severity.

Common Engine Light Codes and What They Mean

Code	Plain English	Typical Fix	Cost
P0171	Engine running lean	Check for vacuum leaks, clean MAF	$0 – $400
P0300	Random misfires	Spark plugs, coils, or fuel injectors	$100 – $500
P0420	Catalytic converter underperforming	Replace cat or O2 sensor	$200 – $2,500
P0442	Small EVAP leak	Tighten gas cap or replace purge valve	$0 – $200
P0455	Large EVAP leak	Gas cap, EVAP canister, or hoses	$0 – $300
P0128	Coolant temp below threshold	Replace thermostat	$150 – $300

ProWhy Steer Is the Best Engine Light Checker

Steer isn't just a code reader — it's a complete vehicle control system. When your engine light comes on:

It reads the code instantly via Bluetooth

Translates it into plain English (no Googling required)

Tells you the severity: Safe, Caution, or Stop

Gives you a clear action plan with estimated costs

Logs everything in your digital vehicle history

Stop driving to the auto parts store. Check your engine light from your driveway.

Engine Light Checker: How to Check Your Engine Light for Free

Key Takeaway