003FF1

What Code 003FF1 Means

Code 003FF1 belongs to a group of faults that can be stored in the engine control unit (DME) on M57 diesel engines when the mass air flow sensor (MAF, LMM in INPA) fails. The source data notes that on the M57, an LMM fault can trigger codes 003F35, 003FF1, 004B10, 004BA0, 004BB6, 004BC1, and 004BC2, read through INPA. Code 003FF1 isn't isolated—it's part of a set of related faults that point to a problem with air flow measurement.

The mass air flow sensor (MAF) measures how much air enters the engine. The DME uses its signal to calculate injection quantity and to manage exhaust gas recirculation (EGR), boost, and other parameters. When MAF readings are off or the electrical circuit (power, signal lines, ground) has a fault, the control unit stores codes that affect how the engine runs.

Symptoms

• Intermittent loss of power (“sometimes there's really no power”).
• According to INPA live data, the Ansauglufttemperatur (intake air temperature) parameter stays at 19.4 and doesn't change.
• The Luftmasse (mass air flow) parameter readings seem implausible—they don't match what's expected.
• Related codes may appear: 003F35, 003FF1, 004B10, 004BA0, 004BB6, 004BC1, 004BC2.

Diagnosis and Repair

Check the Sensor and Its Circuits

1. The LMM has already been replaced (a Pierburg unit is installed). Faults can persist after replacement, so check the electrical connections.
2. Check the signal lines: measured resistance on the Luftmasse signal line is 4.29 kΩ.
3. Check LMM supply voltage: at idle, voltage at the sensor is about 2.5 V.
4. Check voltage at the ECU: a constant 5 V is present on the control unit side.

Next Steps

The source discusses replacing the wiring harness or further circuit testing. Check wire continuity, connector contacts, and ground quality. If the harness is confirmed faulty, replace the damaged sections or the whole harness.