41AA

What Code 41AA Means

Code 41AA points to a fault in the boost pressure sensor or its electrical circuit. The boost pressure sensor measures intake manifold pressure downstream of the turbocharger and sends the signal to the engine control unit (DME). The DME uses that signal to calculate cylinder air charge and adjust fuel delivery and ignition timing.

When 41AA sets, the engine management system sees an implausible signal from the sensor, which can drop the engine into limp mode with reduced power. The cause can be the sensor itself, or wiring and connector problems.

Symptoms

• Loss of engine power, especially under load.
• Engine management drops into limp mode (rpm and torque limited).
• Boost pressure–related faults stored in the engine control unit (DME).
• Possible hesitation and flat spots during acceleration.

Diagnosis and Repair

1. Read the fault codes with diagnostic equipment (ISTA, INPA).
2. Check the boost pressure sensor circuit: connectors, wire integrity, corrosion, and damage.
3. If possible, compare sensor readings against reference values (with a multimeter or oscilloscope).
4. If the sensor is confirmed faulty, replace the boost pressure sensor.
5. After replacement, clear the fault codes and run the adaptation (if needed).

Recommendation: use genuine BMW (OE) parts or quality equivalents that meet the manufacturer's specs.

Secondary Damage

Ignoring 41AA can leave the engine running in limp mode with reduced power, higher fuel consumption, and degraded performance. Over time, incorrect boost pressure data can throw off the air-fuel mixture, which accelerates engine wear and can kill the catalytic converter. Fix the fault as soon as possible.