Jimmy, I'm not sure the 2010 ST (which is a Thai build - VIN starts with 'M') has a DPF in it. The Euro spec 2009 models (Spanish built, VIN starts with 'VSK') vehicles have the DPFs and I think some of the 2010 Spanish ones had the DPF as well, but they dropped the DPF when they went to the 140kW engine.
Then again, it wouldn't surprise me if they slipped one in.
When you first turn on the ignition, there should be a light in the middle at the bottom of the display that looks like a cloud with three lines coming off it, this is the DPF warning light. I don't think the ECU would light that up if the DPF wasn't installed.
If you have a DPF, then have a chat to Robert at ChipIt (he frequently visits this forum). I will be buying a DPF Delete Pipe from these guys (although I want to work out some pressure sensor issues first).
As linked points out, an ECU reset might be a good first step. It's very simple, but quite important that you follow the steps closely. Here they are again:
1) Unload the vehicle so it's as light as possible.
2) Write down the trip meter value in case you use it for recording fuel usage stats
3) Remove the battery negative lead
4) Press the brake pedal for a couple of seconds OR try turning on the ignition
5) Reconnect the battery negative lead
6) Take the vehicle for a gentle run, accelerating very lightly up to 80-90km/h, no more than 2500rpm at any stage
7) Drive like that for a few minutes then stop, turn off the ignition, job complete.
Your vehicle will have learned a lighter fuel mapping. Driving the vehicle hard (accelerating by revving out over 2500rpm) or using full accelerator a lot will "adjust" the fuel map towards the richer, heavier fuel usage again.
