Hello again Eugene,
first of all don't worry about the car having a DPF or not, no early 1.8 Focus had one fitted.
With regard to the fault depending on the diagnostic scanner used not all fault codes are picked up by lower end scanners.
There are a couple of common concerns on this engine, first the fuel filter which you've done so you can hopefully disregard this.
The Exhaust Gas Recirculation (EGR) valve can stick. The only way to detect this other than with a code reader is to use a diagnostic tool that is capable of reading live data, this way the EGR position and MAF signals can be checked to make sure this is operating correctly.
Check the glow plug circuit including the glow plugs, people think the glow plugs are for cold starting only but on modern diesel engines they are for emission purposes so are constantly monitored by the engine management (PCM) if the PCM detects a fault then the warning will be displayed due to it been an emission concern.
Although more expensive I would recommend a Ford dealer using IDS to help diagnose this, the IDS system is a Ford designed system so can interpret the PCM signals and codes better than any other diagnostic tool on this model.
There are other faults that can give these symptoms even down to an instrument cluster fault but start with these points.
Let me know if I can assist further or if you have more questions regarding this and I'll reply as soon as I'm able to.