Can I get a picture of a boost pressure sensor.

Looks like could be caused by one of several sensors.
I did find thisP04D9 EGR feedback saturation This OBD monitor indicates if the burned air fraction error is saturated against a high or low limit. The logic for the monitor evaluates the time spent at saturation and compares the ratio between the time spent in a saturation mode and the total time engine running. A fault is reported whenever the ratio exceeds the fault limit.
P04D9 EGR system: Feedback control(Saturated Low)
Enable conditions: Engine torque 300 - 2500NM,Exhaust Mass Flow 0.1 kg/s, Ambient Air Temperature-8 -55C, Barometric Pressure 75 - 105 kpa, Coolant Temperature>65 C
Disable Conditions No active DTCs P0069 P046c P0234, P0299, P0401, and P0402
Some possible causes
P0069 Intake manifold pressure sensor evaluation
P046c EGR differential pressure sensor: DP Sensor rationality
P0234 Comparison of actual boost pressure, Overboost, to modeled boost pressure
P0299 Boost Pressure: Underboost, Comparison of actual boost pressure to modeled boost pressure
P0401 EGR system (low flow)compare demanded egr flow to actual
P0402 EGR System (High Flow)compare demanded egr flow to actual

P0236 = Possible causes are

1. Boost pressure sensor harness is open or shorted
2. Boost pressure sensor circuit poor electrical connection
3. Faulty boost pressure sensor
4. Faulty Turbo/Super Charger
5. Engine over temperature
6. Ignition misfire exceeds the threshold
7. Faulty Knock sensor (KS)

P0046 = Turbo/Super Charger Boost Control Solenoid Circuit Range/Performance

.... based on this information I would replace the turbo boost control solenoid first.

no turbo means no boost which means no boost pressure sensor

Removal procedure
1.Disconnect harness assembly[1] from boost pressure sensor[2]
2.remove bolts[3] from boost pressure sensor [2]
3.Remove boost pressure sensor [2] from inlet manifold[5]
4.Remove O-ring seal [5]
Installation procedure:
1.Clean and replace worn out components.
2.Install a new O-ring 5 to boost pressure sensor [2]
3.Install boost pressure sensor [2] to to inlet manifold [5]
4.Install bolts[3] to to pressure sensor [2] finger tight.
5.Connect harness assembly[1] to boost pressure sensor[2]

What make and model please.

P0234 Description
The boost pressure sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with accelerator pedal position (APP) and engine speed. The engine control module (ECM) uses this information to assist in diagnosis of the barometric pressure (BARO) sensor and to provide engine overboost protection. The boost pressure sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The engine control module (ECM) supplies 5 volts to the boost pressure sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost pressure sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost pressure sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost pressure sensor. The ECM then compares the predicted value to the actual signal.


Read more: http://engine-codes.com/p0234.html#ixzz2e2DssWbP

Have you changed the MAP sensor (on the intercooler)?
If not, thry to replace it with 3bar sensor, stock is 2.5bar!

If it won't build boost pressure then the most likely problem is the waste gate has failed. there are two types and I need to know the turbo charger type in order to help you more. If you have a vachum operated waste gate the digaphram may be blown or the vachum line broke or the vachum pump has failed.

Computers and Control Systems: Diagnostic Trouble Code Tests and Associated Procedures
P0236
SYMPTOM
P0236-MAP SENSOR TOO HIGH TOO LONG
WHEN MONITORED
Engine running.
SET CONDITION
Boost pressure signal indicates boost pressure is high when other engine parameters (i.e. speed and load) indicate boost pressure should be low or
boost pressure is low when other engine parameters indicate it should be high.
POSSIBLE CAUSES
- Other codes
- Checking boost pressure sensor
- Checking the 5-volt supply circuit
- Sensor ground circuit open
- MAP sensor
- MAP signal circuit open
- MAP signal circuit STV
- MAP signal circuit STSG
- MAP signal circuit STG
- ECM

Ther first code ECM-6805 TURBOCHARGER (TC) CONTROL VALVE DIAGNOSTIC TROUBLE CODE (DTC) INFORMATION If engine speed (RPM) is above 3500 rpm and the engine is operating at a high load, and if the boost pressure (from the boost pressure sensor) is higher than a designated value, which at maximum boost pressure is approximately 20kPa (2.9psi) above normal boost pressure, this is interpreted as a fault and diagnostic trouble code (DTC) ECM-6805 is stored. Condition reduced boost pressure Possible source * hoses between turbocharger (TC) and turbocharger (TC) control valve respectively turbocharger (TC) control valve and pressure servo are loose or are blocked/damaged * faulty turbocharger (TC) control valve * faulty boost pressure control (BPC) valve pressure servo * sticking boost pressure control (BPC) valve Condition * none ECM-6805 TURBOCHARGER (TC) CONTROL VALVE PRESSURE TOO HIGH - PERMANENT/INTERMITTENT FAULT Checking the hoses and turbocharger (TC) control valve Check that the hoses between the intake manifold, pressure regulator and turbocharger (TC) control valve are not trapped, blocked or damaged. Check the turbocharger (TC) control valve by activating it. Check the alignment of the boost pressure control (BPC) valve pressure servo and the boost pressure control (BPC) valve and that they are functioning correctly and not sticking according to See: Component Tests and General Diagnostics\Boost Pressure Regulator, Checking/Adjusting Verification Hint: After carrying out the repair, check that the fault has been remedied. * Ignition off. * Reinstall connectors, components etc. * Disconnect the VCT 2000 from the data link connector (DLC). * Test drive the car and check that high boost pressure is obtained. * Connect the VCT 2000 to the data link connector (DLC). NOTE: Do not switch off the ignition before the VCT 2000 has been connected and the boost pressure has been tested with the smart tool. Read the boost pressure fault status When the boost pressure has been tested the display should show that the diagnostic is complete. the second code Symptoms You will likely not notice any serious drivability problems, although there may be symptoms. Possible Solutions The simplest thing to do is to reset the code and see if it comes back. Then start with the cheapest, easiest repair procedures: Inspect for the following conditions: An incorrectly routed harness--Inspect the harness of the MAF sensor in order to verify that it is not routed too close to the following components: - The secondary ignition wires or coils - Any solenoids - Any relays - Any motors A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. A wide open throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 6-12 g/s at idle to 230 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system. The barometric pressure (BARO) that is used in order to calculate the predicted MAF value is initially based on the MAP sensor at key ON. When the engine is running the MAP sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated MAF value to be inaccurate. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 103 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude. A high resistance on the ground circuit of the MAP sensor can cause this DTC to set. Any loss of vacuum to the MAP sensor can cause this DTC to set. the third code O2 sensor failure may not be displayed appropriatly