C2 catalyst conversion rate too low

Hello!

I'm having a problem with a Citroen C2 with a 1.4 Sagem engine control unit; the MIL (Malfunction Indicator Lamp) occasionally illuminates and then stays on.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

I took two photos, one with the engine idling and one at 3000 RPM. I'd like to hear your opinions on whether it's possible to identify a faulty catalytic converter from these photos.

Thank you very much!

Is the internal mechanism of the KAT solid, or does it rattle?

Yes, it's solid and doesn't rattle.

Should the probe, located behind the catalytic converter (KAT), display a stable, flat line at approximately 3000 RPM?

at approximately 0.5V.

"This can have many causes, which unfortunately are not always easy to identify using the OBD system. Start with the simplest and cheapest things first, and perform a visual inspection of the flexible pipe as well as all the seals in the area of the exhaust manifold, catalytic converter(s), and EGR valve." Check the wiring of the lambda sensor for damage, such as from rodent bites or other causes.

Unfortunately, oxygen sensors do not have a reputation for lasting forever, and for this reason, they are often replaced quickly in workshops. It's also unfortunate that the engine software sometimes goes into "limp home" mode for minor issues, but not for more significant problems, or not at a time that corresponds with the occurrence of the error. Have you experienced an emergency stop yet?

Even if it doesn't always seem logical: Intermittent malfunctions in the ignition system, temporary malfunctions of the EGR valve or idle speed control, a faulty fuel ventilation system, and leaks in the vacuum system can all lead to this error message. The motor software really didn't bother to be logical.


"P.S.: Please check the Long-Term Fuel Trim values to see if the software has made any adjustments. Bolded values may indicate a vacuum leak, unless you have been using E85 or fuel from unknown sources."