Stubborn P0234 Overboost Code

[CutterComp]

Car is a 2001 C70 2.4T auto convertible w/ 98k miles. I just replaced the boost solenoid with a new Pierburg unit and also replaced 2 of the 3 vacuum lines that run from the solenoid to the turbo/wastegate. Frankly, I couldn't see how to access the terminus of the 3rd line without some heavy disassembly on this car and because I didn't know for certain the line was bad, I let it go.

Regardless, this seemed to fix the boost issues the car was having. Car was much smoother and the code was cleared and stayed off for about 2 weeks. Now the code is back. I don't actually have access to the car at the moment, it belongs to a friend. I'm hoping to get an idea of culprits before I go to the trouble of getting the car back here to my shop.

One possibility is that the new boost solenoid failed. Being a quality brand, I hope that's not the case but...
Another option is the 3rd vac line I didn't replace has failed. Chances of that are slim in a two week period but...
Third option would be the MAP sensor? Does this car have just one pressure sensor? Where is it located?
Fourth option would be an issue with the wastegate itself. Any good tips for looking into this possibility?
Fifth could be general wiring/ECU faults...

Hoping some folks that know Volvos much better than I do can point out which culprits are most likely in this scenerio or point out some options I haven't considered.

Thanks.

[abscate]

ECM 6805 which maps to P0234 calls for checking all three hoses from turbo to valve and resetting waste gate using a small high resolution pressure gauge , to spec. Ipd carries that gauge.

The MAp sensor lives in the hard pipe after the intercooler, just under the left side of the intake manifold. Careful with those, they are expensive

[RickHaleParker]

ECM-6805 ( P0234 ) Turbocharger (TC) control valve. Pressure too high. Permanent/Intermittent fault

Condition
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.

Substitute value
reduced boost pressure

Possible source

• 1. Hoses between turbocharger (TC) and turbocharger (TC) control valve respectively turbocharger (TC) control valve and pressure servo are loose or are blocked/damaged
  2. Faulty turbocharger (TC) control valve
  3. Faulty boost pressure control (BPC) valve pressure servo
  4. Sticking boost pressure control (BPC) valve

Fault symptoms
none