It's had a new diesel filter new air filter
But have you addressed the issue that if generating the MAF low voltage code?
There's no point in changing random stuff that's not relevant to the code, it's a waste of time and money.
If the MAF is saying low voltage, you need to concentrate on why.
Automotive diagnostics needs to follow a mathematical path, or you'll simply waste time and money, changing components that aren't faulty to start with.