A4 8D: Documenting Performance Issues (Solution)

Sudden performance drop, error code 00575 (intake manifold pressure) stored in the engine control unit's fault memory.

Affected vehicle identification numbers:
Bis 4B1 N 000418.
Up to 4D1 N 000149.
Bis 8DY A 119999.



Cause.
If the engine control unit detects a too low or too high intake manifold pressure (boost pressure), it switches to a limp-home mode, and the engine power is significantly reduced by adjusting the fuel injection quantity.

a. If the boost pressure is too low (below the regulation limit), it is likely that no vacuum will reach the vacuum chamber of the turbocharger's wastegate actuator. In such cases, the most common cause is not the boost pressure control valve itself, but rather cracked vacuum hoses or torn angled connectors.
b. If the boost pressure is too high (exceeding the regulatory limit), the cause is usually a sticking or jammed turbocharger wastegate actuator.




Solution:
a. Check the entire vacuum hose system for leaks using the manual vacuum pump. Replace any faulty fittings if necessary. If the vacuum hose system is in good condition, check the turbocharger's impeller adjustment.
b. Disconnect the vacuum hose from the vacuum sensor on the turbocharger and connect the hand vacuum pump to the vacuum sensor. The linkage for the guide vane adjustment must move freely without sticking.
Otherwise, the turbocharger must be removed, and the test must be repeated on the removed part.

If the exhaust manifold adjustment is stuck or jammed, the exhaust manifold with the compensator pipe must be removed and carefully inspected. There is a possibility that the exhaust manifold and compensator are corroded internally, or that the internal pipes are broken.

Rust particles and metal parts can detach and enter the turbine wheel of the turbocharger with the exhaust gas flow. As a result, the adjustment mechanism of the guide vanes is damaged.

To prevent repeat damage, replace the turbocharger and exhaust manifold components.