if you had VCDS it would be much easier to diagnose.
but we can reach some conclusions without it.
if the steering with engine running is as stiff as when the car is turned off then you have either a power supply
problem or steering pump
problem.
if the dash light is ilumminated but you still have some assistance but not has much as it would be normal then the steering angle sensor could be to blame or the new pump code since you need to code if it uses the G85 or G250 sensor.
regarding the power supply
problem:
- check fuses above the battery
- check battery voltage when engine is running, should be 14V or close
- check if battery light appears when engine is turned off disappears when the engine is running
---------- if it not appears with the engine stopped then you have a load wire
problem
----------- if it doesn't disappear with engine running then you have an alternator
problem
- make sure the battery is fully charged.
- if all the above is good check if you can see some wiring damage, or corrosion in the earth wire of the steering pump.