2009 VW Passat CC 2.0TDI (CBBB engine)

Had three codes come up on the scanner: 01348, 09326 and 09327 - all refer to Exhaust Gas Temperature Sensor (Circuit Bank 1 Sensor 4 it appears).

Glowplug flashing amber warning light comes up and then the amber check engine light. Codes can be cleared but come back fairly soon.

When this happened some time ago, I took it to a VW mechanic and I noticed they were working under the windscreen - removing built-up carbon from the looks of it and said I'd probably have to get it done again in a few years.

With this engine, the EGR and ASV are right at the mid-front of the engine, so I'm not really sure what the mechanic was cleaning out last time (couldn't have been the DPF?).

Anyway, I decided, as a first step to buy Liqui Moly "Diesel Engine Intake Decarb", to see if the issue is being caused by carbon build-up.

I have used a DPF cleaner solution fairly regularly (added to fuel tank) and gone on long trips in Sport mode to try and keep things in check. I have also used a diesel fuel additive to keep the fuel system clean. Additionally, I do regular oil changes with a good quality (DPF compatible) engine oil.

Any opinions on the Liqui Moly Decarb?

Is the issue likely to be a clogged Temperature Sensor?

Is this sensor easy to access/remove and replace (not too expensive)?

Any other thoughts or experiences with this?