An electronically controlled heavy-duty diesel engine develops an intermittent 'Low Boost Pressure' fault code. The technician notes that the fault often appears under heavy acceleration. Which of the following is the most likely cause, assuming no active leaks?

Question: An electronically controlled heavy-duty diesel engine develops an intermittent 'Low Boost Pressure' fault code. The technician notes that the fault often appears under heavy acceleration. Which of the following is the most likely cause, assuming no active leaks?

Answer options: ✅ A failing variable geometry turbocharger (VGT) actuator or stuck VGT vanes.

• A plugged engine air filter reducing air intake to the compressor.
• An excessively worn turbocharger bearing causing compressor wheel contact.
• A faulty exhaust gas temperature (EGT) sensor providing incorrect readings.

Correct answer: A failing variable geometry turbocharger (VGT) actuator or stuck VGT vanes.

Explanation: A failing VGT actuator or stuck VGT vanes prevent the turbocharger from properly adjusting its geometry to optimize boost pressure across varying engine speeds and loads. Under heavy acceleration, the VGT system should adjust to maximize boost quickly; if it can't, low boost pressure will result. A plugged air filter would generally cause continuous low boost, not intermittent. Worn bearings would likely cause noise or oil leaks, and an EGT sensor wouldn't directly cause low boost.