Despite these benefits, such turbochargers can be prone to problems. The vane mechanism is easily affected by carbon build-up, which can cause the mechanism to jam. This can occur quite quickly if the vehicle is used predominantly for short journeys where the engine is not allowed to get up to full operating temperature. The mechanism may jam in either the fully open or fully closed position resulting in no boost or too much boost from the turbo. If the turbo over-boosts there is a real danger that it’s internal components will be damaged, resulting in the need for a complete replacement unit. In many cases, the computer controlling the engine will sense a fault and will severely limit the engine’s performance in what is called a “limp-home” mode to prevent any further damage. Low boost may also cause black smoke under acceleration. The problem may clear itself by cycling the ignition switch, but it is very likely that the problem will recur.
Previously, the VNT mechanisms could only be calibrated by the original manufacturer. However, Turbo Technics have developed equipment to reproduce the factory calibration (see VTR100 and VTR200) and this is no longer a barrier to remanufacture.