The turbo is probably working as it should be. However, its boost
pressure may not be getting to the sensor inside the injection pump.
That's usually because the "banjo fitting" (on the very aft end of the
intake manifold) is clogged. Simply remove the (hollow) bolt and use a
piece of wire to clean it out, also clear the fitting on the plastic
tube. Then follow that plastic tube to the injection pump to make sure
it's not broken or disconnected.
The turbo's maximum boost pressure is about 11 psi. A pressure gauge
attached to the banjo fitting can confirm that if the problem continues.