I'm seeing a P0245/16629 – Solenoid Valve (A) for Boost Pressure Control (N75): Short to Ground – code on our 2002 ALH TDI. The solenoid valve controls the boost by moving the vacuum actuator that controls the turbo vanes. I think it does this by PWM (pulse width modulation) of the solenoid on the ground side. As I understand it, a (hard) short to ground would result in loss of control over the solenoid which should produce a full or even over boost condition.
What I'm actually seeing little or minimal boost. Vacuum is delivered to the actuator and I can see the actuator move. But boost pressure does not increase much (way less than the ECM is asking for) and the engine doesn't feel like it is getting any significant amount of boost (so while I haven't tested the MAP (manifold absolute pressure) sensor, I'm inclined to believe it.
So this leaves me wondering what the P0245/16629 code actually tells me. Does it indicate:
That the ECM has measured the output pin for the solenoid and actually detected a short, or
The ECM is unable to control the turbo output and infers a short as the likely cause.
Does anybody know? Both static tests on the solenoid wiring and its behavior strongly lead me to suspect that it is the later – I don't see a short to ground with a meter and the solenoid and actuator seem to be doing what the ECM is asking of them.