When you plug in your OBD2 scanner and see a status labeled “CAT”, you might wonder—what is it really telling you?

Let’s decode what “CAT” means on a code reader and how VDIAGTOOL VD70S takes catalytic converter analysis to the next level, even simulating high-end FTIR-style diagnostics—without the high-end lab.

What Does CAT Mean?

On a code reader, CAT stands for Catalyst Monitor, and it refers to the system that checks whether your vehicle’s catalytic converter is working efficiently.

The catalytic converter is key to reducing harmful emissions like CO (carbon monoxide), HC (hydrocarbons), and NOx (nitrogen oxides). The CAT monitor verifies that the converter is properly converting these gases into less harmful substances before they exit the exhaust.

You'll usually see one of three CAT monitor states on your scanner:

● INC (Incomplete) – The catalytic monitor hasn't finished its check yet.

● OK (Complete) – The system has run its diagnostic, and the catalyst passed.

● N/A (Not Applicable) – This test isn't supported on your vehicle.

Why It Matters

A failing catalytic converter won’t just hurt your emissions test—it can trigger poor fuel economy, sluggish performance, and persistent CEL codes like P0420.

So while “CAT” might look like just a simple monitor on the screen, it’s often your first clue that something deeper is wrong with your exhaust system.

VD70S: Smarter CAT Diagnostics with Simulated FTIR Insight

High-end emissions testing tools use FTIR (Fourier-transform infrared) spectroscopy to analyze exhaust gases in real time. While that's overkill for a home garage, the VDIAGTOOL VD70S mimics some of the same data-driven insights—right from your OBD2 port.

Live O2 Sensor Graphing

VD70S lets you view upstream and downstream O2 sensor voltages side by side. If the downstream sensor is mimicking the upstream one, your converter isn’t doing its job.

Catalyst Efficiency Check

Using fuel trim + O2 sensor analysis, VD70S evaluates catalyst conversion indirectly, showing when the system isn’t reducing emissions efficiently—similar to how lab tools check real-world gas behavior.

Readiness Monitor Override

Need to prep for a smog test? VD70S shows CAT readiness in real time and helps identify why the test might not complete, with tips for completing drive cycles faster.

Smart Diagnostics

With freeze frame data and stored code tracking, VD70S lets you catch intermittent catalyst issues that cheaper tools miss.

Bottom Line

“CAT” isn’t just another code reader acronym—it’s your car’s way of saying, “Hey, is my catalytic converter doing its job?”

And with tools like VDIAGTOOL VD70S, you’re not just reading monitor status. You’re getting smart, real-time insight into the heart of your emissions system, with advanced features that feel like lab tech, without the lab coat.

Looking to get serious about emissions troubleshooting?

The VDIAGTOOL VD70S makes CAT diagnosis clean, clear, and cost-effective.