AutoZone will scan your check engine light for free, but the scan only reads the code your car's computer stored — it doesn't diagnose the problem or tell you how to fix it.

When your check engine light comes on, AutoZone's in-store diagnostic scanner pulls the diagnostic trouble code (DTC) that triggered the light. This is a five-character code like P0420 or P0128 that points to a system or component — your catalytic converter, oxygen sensor, thermostat, or dozens of other possibilities. The scan takes about 10 minutes and costs nothing.

What you get is a printout with the code and a plain-language description of what system it relates to. What you don't get is confirmation that the part named is actually broken, what caused the problem, or whether it's safe to drive. A P0420 code means "catalyst system efficiency below threshold," but it could mean a bad catalytic converter, a faulty oxygen sensor, an exhaust leak, or a misfire in the engine — each with a different fix and different cost.

Key Takeaways

  • AutoZone's free scan reads one piece of information: the diagnostic code your car's computer stored, which narrows the problem to a system but not a specific part.
  • The same code can point to multiple different problems, so the scan result is a starting point for diagnosis, not a diagnosis itself.
  • AutoZone does not perform a physical inspection, test individual components, or clear the code without your permission.
  • If you decide to have the work done elsewhere, bring the code printout with you so the shop doesn't have to scan again.
  • Some codes indicate a serious problem (like a misfire) that can damage your engine if you ignore it; others are minor and can wait.

How the AutoZone scan works and what the code means

When you bring your car to an AutoZone store, an employee will connect a handheld scanner to the OBD-II port under your steering wheel. This port is standard on all cars sold in the United States since 1996. The scanner reads the code stored in your car's onboard computer and displays it on a screen.

The code itself is a standardized five-character identifier. The first character is always "P" (for powertrain), followed by a number that narrows the category — P0xxx codes relate to fuel and air, P1xxx codes are manufacturer-specific, and so on. The remaining three digits point to a specific system: oxygen sensor, catalytic converter, transmission, knock sensor, and hundreds more.

AutoZone prints out the code and a brief description. For example, P0171 prints as "System Too Lean (Bank 1)," which means your engine is running with too little fuel relative to air. This could be caused by a faulty oxygen sensor, a fuel injector problem, a vacuum leak, or a bad mass airflow sensor. The code narrows the search but does not identify which one.

What AutoZone's scan does not tell you

The scan reads stored codes only — it does not perform live testing, measure sensor output, or physically inspect anything. It cannot tell you whether the part the code points to is actually faulty or whether something else upstream caused the code to set. It also cannot tell you how urgent the problem is.

Some codes indicate a serious issue that can cause engine damage if ignored — for instance, a misfire code (P0300 series) means your engine is misfiring, which can overheat the catalytic converter and destroy it within hours of driving. Other codes, like a pending code that has not triggered the light yet, may indicate an intermittent problem that comes and goes. The printout does not distinguish between them.

AutoZone also does not clear the code. If you want the light turned off, you need a mechanic or a dealer to clear it after the underlying problem is fixed — or after a certain number of drive cycles if the problem was temporary and has resolved on its own.

When to get a second opinion from a mechanic

If the code points to an expensive part — a catalytic converter, transmission, or engine control module — or if you are unsure whether the problem is urgent, take the printout to a trusted mechanic or dealer before authorizing any work. A mechanic can perform a more detailed diagnosis: testing sensor output with a multimeter, checking for vacuum leaks with smoke, or pulling live data from your car's computer to see what the sensors are actually reading in real time.

This second diagnosis usually costs $75 to $150, but it can save you hundreds by ruling out unnecessary repairs. For example, a P0420 code might lead a shop to replace a $400 catalytic converter when the real problem is a $30 oxygen sensor — a mechanic's live data test can tell the difference.

If you decide to have the work done at a shop other than AutoZone, bring the code printout with you. The shop can see what AutoZone found and does not have to scan again, which saves time and money.

Is it safe to drive with the check engine light on?

It depends on the code. If the light is solid (not flashing), the problem is usually not an when ready threat to your engine, and you can drive to a mechanic. A flashing check engine light means your engine is misfiring, which can damage the catalytic converter and other components — you should not drive except to get to a repair shop.

AutoZone's printout will tell you the code but not whether the light is flashing or solid. If you did not notice when the light came on, ask the AutoZone employee whether they saw a flashing light when they scanned. If you are unsure, assume it is not safe to drive and have the car towed or driven directly to a mechanic.

What to do after you get the scan results

Read the code description and search for it online along with your car's year, make, and model. You will find forums and repair guides that list common causes for that specific code in your vehicle. This can help you decide whether to take it to a mechanic right away or whether it is safe to drive.

If the code is something you recognize — for example, you recently had work done and the light came on after — call the shop that did the work and describe the code. They may have caused the problem and can fix it under warranty.

If you decide to have a mechanic diagnose it further, call ahead and ask whether they charge for a diagnostic. Some shops waive the diagnostic fee if you have the work done there; others charge a flat fee or an hourly rate. Knowing the code in advance can reduce the time they spend diagnosing, which may lower the cost.

Frequently Asked Questions

Can AutoZone clear the check engine light?

No. AutoZone can only read the code and print it out. Only a mechanic, dealer, or diagnostic scanner you own can clear the code. The light will come back on if the underlying problem is not fixed, because your car's computer will set the code again.

Will the scan work on my older car?

Only if it was made in 1996 or later. Cars before 1996 do not have the OBD-II port and require a different type of scanner. If your car is older, a mechanic can still diagnose the problem, but AutoZone's free scan will not work.

What if AutoZone scans my car and finds no code?

If the check engine light is on but no code is stored, the light may be a false alarm, or the code may have cleared itself. Drive the car for a few days and return to AutoZone to scan again. If the code returns, bring the printout to a mechanic for further diagnosis.

Can I use the AutoZone scan result to negotiate a repair price?

Yes. Bring the printout to a mechanic and ask them to confirm the code and diagnose the cause. If they recommend a repair, ask them to explain why that part is the problem and not something else the code could point to. A good mechanic will walk you through their reasoning.

Does the scan tell me if my car will pass inspection?

No. A check engine light will fail a state inspection in most places, but the scan does not tell you whether the underlying problem is fixable or how much it will cost. You need a mechanic's diagnosis to know whether the repair is worth doing before inspection.