Cleared Codes: How Sellers Hide a Check Engine Light

Here's a trick we see all the time. A car has a check-engine light. The seller clears it right before the sale. The light is off when you look, so you think the car is fine.

How it works

Clearing a code turns off the light. But it also resets the car's "readiness monitors" — the self-tests the car runs as you drive.

Those monitors take time and miles to finish. So right after a code is cleared, they aren't done yet.

How we catch it

We run a full OBD-II scan. If the light is off but the monitors aren't set, that's a red flag. It often means a code was cleared in the last day or two.

It also means the car may not pass smog yet, even if it looks clean.

Why it matters

The light comes back. When it does, the problem is yours, not the seller's. A scan before you buy puts that risk back where it belongs.

This is one of our most important checks. It's quick, and it saves buyers a lot of pain.