What does it mean?
Upon retrieving a turbocharger/supercharger boost control solenoid open circuit code from a turbocharged or supercharged vehicle, I know that the powertrain control module (PCM) has detected one of two possible conditions: Either an open circuit in the turbocharger or supercharger boost control solenoid has been detected or an unacceptable boost pressure sensor input has been detected.
Although both the turbocharger and supercharger are forced air induction devices, they are very different in design. The turbocharger utilizes engine exhaust to generate turbine operation. A specially designed exhaust manifold (or manifolds) allows spent engine exhaust gases to enter the turbocharger on the turbine side. On the opposite side of the turbocharger there is an impeller housing which is mated to the engine intake manifold via aluminum or silicon hoses.
This design permits the turbocharger to capture hot engine exhaust gases, compress them under high RPMs, and reintroduce them to the engine as forced air induction. Most turbocharged vehicles are also equipped with an air or cold water intercooler. In order to introduce cooler, denser air into the engine, high-pressure air from the impeller is forced through the intercooler before entering the engine.
The intercooler is typically located in front of the radiator or air conditioning condenser so that ambient air may flow through it when the vehicle is in motion. Superchargers are a bit more complex in design than the turbocharger. There are two popular supercharger setups. The first is a roots-type supercharger. This type of supercharger is bolted to the cylinder head/s in place of the intake manifold.
It functions as the intake manifold with one exception; it also has a compression device that includes roller-type pistons. The roots-type supercharger is belt-driven using the engine crankshaft. The second supercharger design is a centrifugal supercharger. It is typically bolted to the face of the engine with specially made brackets and bolts. This type of supercharger is also belt driven using the engine crankshaft.
It is designed much like an air conditioning compressor and uses rolling pistons to compress air that will be forced into the engine combustion chambers. These types of compressors are usually aftermarket components and require a stand-alone boost controller that interacts with the factory PCM. Because of the nature of turbocharger and supercharger operation, as engine RPM levels increase, so do the RPM levels of the respective device.
Most forced air induction devices don’t even begin to effect engine performance until the 2,000 RPM range. These forced air induction devices can reach internal RPM levels of 250,000 under peak boost conditions. Of course, these extreme RPM levels can produce air pressure that is far higher than that of atmospheric pressure. This compressed air is known as “boost pressure”. Turbocharged and supercharged vehicles use forced air induction to increase engine performance.
These types of vehicles are often equipped with smaller engines. The introduction of a turbocharger or supercharger permits these smaller engines to perform at a level comparable to that of a much larger engine. These vehicles require a very particular fuel delivery and engine drivability strategy. The PCM is programmed for increased fuel delivery, higher engine temperatures, and turbo boost pressure regulation.
Because of the possibility of engine damage that may occur from excessive boost pressure, it must be regulated using a wastegate or a bypass valve. Excessive boost pressure is relieved by allowing it to either vent into the intake system or a specially designed reservoir; until it can be gradually reintroduced into the engine intake system. The turbocharger/supercharger bypass valve may be an electronically controlled solenoid that actuates the opening of the bypass valve.
When the PCM detects an overboost condition, a voltage signal is applied to the bypass control valve