What causes the Audi to report an unreliable boost pressure signal?
2 Answers
Audi reports an unreliable boost pressure signal because the Audi 1.8T engine is a turbocharged intercooled engine. The intake pressure sensor is located between the intercooler and the throttle body: After passing through the air filter, air enters the compressor side of the turbocharger. At this point, the intake pressure is not the pressure entering the engine; it still needs to pass through the intercooler. After the air exits the intercooler, it enters the combustion chamber. Therefore, the intake pressure sensor is positioned between the intercooler and the throttle body. Function of the intake pressure sensor: The intake pressure sensor detects the absolute pressure in the intake manifold behind the throttle valve. Based on the engine speed and load, it detects changes in the absolute pressure within the manifold and converts this into a signal voltage sent to the electronic control unit (ECU). The ECU uses the magnitude of this signal voltage to control the basic fuel injection quantity.
I previously encountered an issue where my Audi displayed an 'unbelievable boost pressure signal' warning. The car noticeably lacked power during acceleration, and the engine warning light came on. At the repair shop, the mechanic read the fault codes with a diagnostic computer and inspected the vacuum lines connected to the sensor, discovering a small cracked pipe that was leaking air. He explained that this 'unbelievable signal' issue usually stems from a few common causes: either the pressure sensor itself is faulty, the connecting pipes are leaking or crushed, the turbocharger's solenoid valve is stuck, or the turbocharger itself is failing—possibly due to carbon buildup jamming the vanes or severe wear. Fortunately, in my case, just replacing the pipe fixed the problem. However, a friend's car had a solenoid valve failure, which was much more expensive to repair. I recommend getting it checked immediately when this warning appears, especially since the loss of power at highway speeds can be quite dangerous.
