Buying a Used Car from a private seller in California? PPI

Watch Out: This Trick Could Cost You Thousands

In California, a Smog Check is a required part of registering a vehicle under a new owner’s name. If the car doesn’t pass the test, you may not be able to complete the registration process and legally drive the vehicle. Some sellers know this and use a trick that the average buyer would never notice.

How Does the Trick Work?

When an expensive catalytic converter fails, the Check Engine light usually comes on. Instead of spending thousands of dollars on repairs, some dishonest sellers install a device designed to hide the problem.

What do they do?

They install a special mechanical or electronic spacer (O2 spacer/simulator) on the oxygen sensor (O2 sensor).

How does it work?

The spacer moves the sensor away from the exhaust stream or alters the sensor’s signal. As a result, the vehicle’s computer is fooled into thinking the catalytic converter is working properly, and the Check Engine light stays off.

Why Is a Basic Diagnostic Scan Not Enough?

Many buyers bring a simple OBD2 scanner when inspecting a vehicle before purchase.

The scanner may show:

 🔧 No trouble codes

 🔧 No Check Engine light

 🔧 No obvious drivability issues

The vehicle may seem perfectly fine.