Hello! My Focus MK 3 2.0 Tdci, 150 horsepower, 180,000 kilometers, has been having problems with DPF regeneration for some time. Low temperature error and regeneration stops. There is also an error for low voltage on the temperature sensor - Bank 1, Sensor 3. I ran Forscan with live data and EGT11V is almost always below 5 volts, sometimes drops to 3.5 volts. I would like to replace this sensor, but I don't know exactly which one it is. There is one DPF sensor, one before it, and one after it. Could you help me identify it? I am attaching photos from Forscan. Thanks in advance, greetings!

Welcome!
I always search for information from multiple sources e.g.:
https://www.autocodes.com/p242c.html
It says No. 1 is closest to engine and gives some resistance values.

I can't see "LOW" voltage on the sensor, your screenshot shows P242C Voltage above threshold and anyway, the temperatures, to me, look "sensible" i.e. not stupid (depending on engine conditions) but it could be an intermittent fault?

I'd disconnect sensors in turn to see which Forscan data PID matches with which physical sensor.
Then test sensor resistance (if it is as shown on the page and heat it up with match or blowtorch to see what happens with resistance and then connected back up, the temperature indicated in Forscan)
Then if that doesn't make sense then carefully check all wiring back to PCM (that is getting more difficult)

Beyond that:
My only other thought, is this the rubbish post-injection method of getting extra fuel in to regenerate the DPF (or a vaporiser plug) AND
What about looking at the DPF pressure differential sensor for values at idle and 3000 rev/min and any blocked pipework etc.

That's just some initial thoughts...

Thanks for the answer and advice. It all started about a month ago - the malfunction light came on, it turned out that it was due to too many unsuccessful regenerations due to low DPF temperature. I started a forced regeneration with Forscan and it stopped again with the same error - low temperature. Then I dismantled the nozzle for injecting additional diesel, washed it with MAF cleaning spray, washed and blew the entire route. I measured the resistance of the heater 0.9 ohms. I put everything back together and started a forced regeneration 2 times in a row, which lasted about 40 minutes. Now there was already strong heat blowing from the exhaust and it smelled stronger and strange, but there was no visible smoke. Then I took a light out of the passenger compartment to know when regeneration started - I took a signal from Relay 3 in the box by the engine. Then for about 1500 km. it did 4-5 successful regenerations. And now again - low temperature. I removed and cleaned the so-called. evaporator - nozzle, but this time there is no effect. On live data during regeneration on the move EGT12 raises to 500 degrees Celsius, and EGT11 to about 400 degrees. DPF is currently at about 150% Differential pressure at revolutions is almost 0, and at 3000 revolutions about 10-12 millibars

Those pressure figures actually sound too fine (normal 0-10 mBar idle, 40-80 with 100 mBar Max at 3000) - worth a check. If you are certain DPF is clean.
Aerosols like Jimmy, see below, uses are available on e-bay:
https://www.ebay.co.uk/itm/167576505252

Once clean, parameters can be reset.

I suggest looking at O'Rileys Autos
https://www.youtube.com/@ORileysAutos

Jimmy is my Go To for DPF issues, he doesn't recommend forced regens as they can damage DPF due to very high temperatures but you'll see his methods and measurements.
It looks like your vaporiser is working and clear but the resistance is IMHO borderline low and fuse will blow if it gets much lower.

There are multiple other factors including faulty sensors that need looking at on live data, if no specific fault codes...