P112E

What the Code Means

P112E is the OBD2 equivalent of the BMW-specific fault 120308. It indicates that the engine control module (DME) has detected insufficient boost pressure. The code sets when actual boost pressure is significantly below target, which usually points to mechanical problems in the turbocharging system.

The BMW turbocharging system includes the turbocharger, the wastegate, vacuum lines, the manifold absolute pressure (MAP) sensor, and the actuators. The DME calculates target boost from engine load, rpm, and other parameters, then compares it against the MAP reading. A deviation beyond the allowed threshold sets the code.

Symptoms

• Engine: power loss, reduced throttle response, sluggish acceleration
• Behavior: the car “won't pull,” especially during passing or on inclines
• Indicators: Check Engine Light (CEL) on

Diagnosis and Repair

Step 1: Check the Vacuum Lines

Inspect the vacuum hoses for cracks, separation, or disconnected fittings. Pay close attention to the lines running to the wastegate solenoid.

Step 2: Check the Wastegate Solenoid

Test the wastegate solenoid with ISTA or INPA. Make sure it opens and closes on command from the DME.

Step 3: Check the MAP Sensor

Read the MAP sensor at idle and under load. Compare against reference values. Replace the sensor if it doesn't match.

Step 4: Check the Turbocharger

Inspect the turbo for shaft play, damaged compressor wheel, or a stuck wastegate. Check that the wastegate actuator moves freely.

Common Diagnostic Mistakes

• Replacing the turbo without checking the vacuum system
• Ignoring leaks in the intake tract

Repair Options

• Replace damaged vacuum hoses
• Replace the wastegate solenoid
• Replace the MAP sensor
• Repair or replace the turbocharger

Secondary Problems

Ignoring P112E can lead to:

• Catalytic converter damage: a rich mixture from low boost can overheat the catalytic converter
• Lower fuel economy: the DME goes into limp mode and increases fuel consumption
• Further turbocharger failure: poor lubrication or overloading can destroy the turbo bearings
• Intercooler and intake tract damage: oil from the turbo can be pushed into the intake

Running with this code for a long time can significantly raise repair costs as related components fail.