P0234: Turbocharger Boost Pressure Too High (Overboost)

P0234 on the Mercedes Sprinter VS30 means the turbocharger produced more boost than the ECU commanded (overboost). The OM642 uses a variable-geometry turbocharger (VGT) whose vanes are actuated to control boost. If the vanes stick closed, or the boost control actuator/solenoid misbehaves, manifold pressure can exceed the target and trip P0234. The ECU protects the engine by cutting fuel and dropping into limp mode when overboost is detected. Carbon buildup on the VGT vane mechanism is a known OM642 issue and a frequent root cause. Less commonly, a faulty boost pressure sensor reading high, or a sticking wastegate/actuator, will set this code. Diagnose with live boost data before replacing the turbo.

• Boost pressure of turbocharger 1 is too high.

• Limp mode / sudden power cut under acceleration
• Check engine light
• Surging or fluctuating boost feel
• Whistling or unusual turbo noise
• Reduced fuel economy

• Sticking variable-geometry turbo vanes (carbon buildup) — common on OM642
• Faulty turbo boost control actuator or solenoid
• Boost pressure sensor reading high
• Vacuum/electrical control fault to the VGT actuator
• Wastegate or actuator sticking closed

1. 1Scan and record all codes; note related boost codes (P0299, P0045, P0046).
2. 2Check freeze-frame for boost (actual vs. commanded), RPM, and load at the time of the fault.
3. 3Monitor live boost pressure on a test drive — watch for overshoot above the commanded value.
4. 4Inspect the VGT actuator linkage for sticking and the vanes for carbon buildup.
5. 5Test the boost control actuator/solenoid operation and its electrical/vacuum supply.
6. 6Verify the boost pressure (MAP) sensor reads accurately at key-on and idle.
7. 7If the VGT mechanism is seized with carbon, clean or replace the turbo as required.

1. 1Repair or replace leaking charge-air (intercooler) hoses and clamps.
2. 2Clean or replace a turbo with sticking variable-geometry vanes.
3. 3Replace a faulty MAF, MAP/boost-pressure sensor.
4. 4Replace the boost-control actuator or solenoid.
5. 5Replace a restricted air filter and clear the intake tract.

• Turbo boost control actuator/solenoid~$120–$400
• Variable-geometry turbocharger~$900–$1,800 if vanes seized