Do you have a 2011 car with timing chain? At some point, they converted the DPF light to mean that you need a new timing chain. If you have replaced the timing chain, there is a good chance that you need to do some kind of reset to tell the ECU that the chain is now good.
If you have replaced the DPF and the pressure sensors, you may still need to a reset to take the counter back to zero.
I am not sure about the fuel injectors. The injectors go well but they leak from the seals which needs replacement. If there is fuel leak, then the oil needs more frequent changes. But I do not think it can trigger a DPF light.
If you have both a new timing chain and a new DPF with sensors and you are still in limp mode, something serious is going on. A new chain, a new DPF and new sensors, sound expensive even if you DIY.