If you drive a turbocharged vehicle, be it a high performance sports car or a robust turbo diesel ute, the distinctive 'kick' and hissing whine of your turbocharger switching on at high revs can become a very comforting and familiar sensation. This makes it all the more unnerving when your turbocharger doesn't function when it should, and the effects of lost turbo power are readily noticeable in even the most modest of turbocharged vehicles.

However, discovering the cause of an underpowered turbo or complete loss of turbo power can be challenging, as turbos are relatively complex devices that can be affected by a number of potential faults. While taking your turbocharger in for professional repairs and servicing is always the most efficient way to tackle this problem, you may be able to ascertain the source of the problem yourself by keeping an eye out for the following signs and symptoms:

Leaks

Turbochargers are reliant on precise control of air pressure to function properly, and even the tiniest leak or hairline crack can release internal gases and dramatically undermine the turbo's functioning power. Any underpowered turbocharger system should subsequently be checked for leaks; be sure to be thorough, checking all hoses and fittings and ensuring seals, o-rings and gaskets are fully intact. Professional leak detection can greatly speed the process of finding a turbo leak.

Excessive engine heat

Generally speaking, an engine fitted with a turbocharger will create more heat than a naturally aspirated engine (although this is far from universal), which can have a dramatic effect on your engine's oil reservoirs. The additional heat created by a turbocharger can cause engine oils to denature and separate over time, reducing its lubricating heat conducting properties and depriving your turbo of vital cooling power.

The build up of heat caused by denatured oil can quickly cause a turbo to fail, and may even cause permanent damage if the turbo is allowed to run hot for too long. As such. if you notice excessive engine heat combined with loss of turbo power you should seek mechanical aid as soon as possible.

Clogged or damaged filters

The air intakes on any turbocharger are fitted with fine mesh filters, which prevent solid detritus such as dirt, grit and leaves from entering the turbo and clogging up its internal workings. These filters much be cleaned periodically, or they will become clogged and deprive the turbo of vital air, creating a noticeable drop in power. Be sure to inspect your turbo's air filters regularly for excessive debris, or have them professionally cleaned.

By the same token, a badly damaged filter that allows too much solid debris into your turbo can also cause a severe loss of turbo power, preventing air from circulating within the turbo's main housing. Besides a loss of turbo power, this problem can cause other worrying symptoms such as rapid heat build-up and unnerving knocking noises. 

If one or more of your turbo's filters has become too badly damaged to function, exchanging it for a new one is vital. However, you should also take your vehicle in to have its turbocharger professionally inspected for potential damage -- your turbo may have lacked proper air filtration for longer than you realise, causing extensive damage to its internal workings.