Can you reset a check engine light?

Here’s how to reset a check engine light

There are two ways to clear a trouble code and reset a check engine light.

• Using a code reader or a scan tool, use the clear code function

• Disconnect both the positive and negative battery terminals and touch them together for at least two minutes. This will erase the history, pending and current codes. But it will not erase any permanent codes (there’s no way to clear a permanent code except to fix the underlying problem that caused the code).

A check engine light means there are trouble codes stored in the computer

Resetting the check engine light doesn’t fix the problem

You’re not kidding anybody if you think that resetting the check engine light actually fixes anything. If the underlying problem is not fixed, the check engine light will return after some driving.

Can you reset the check engine light to pass emissions testing or smog check?

Nope. They’re not that stupid. Every vehicle computer is programmed to conduct tests on each emissions system. These are called readiness monitors. If the system passes the test cycle, that system’s monitor is set to the “Ready” state. If the system fails, the monitor will read “NOT READY.”

When you clear trouble codes, you also reset all the readiness monitors to the NOT READY state. If you take your vehicle in for a smog check, the testing facility can instantly see that the monitors are not ready and that’s an instant fail.

What is a permanent trouble code?

A permanent trouble code is one that refers to a critical emissions issue and the code can’t be erased either by disconnecting the battery or by clearing with a scan tool. So even if you use a code reader or scan tool and click on “clear trouble codes,” the check engine light will still light up and the permanent code will still be there.

The ONLY way to clear a permanent trouble code is to fix the underlying problem and then drive the vehicle until it passes the readiness monitor testing.

©, 2023 Rick Muscoplat