2021-2024 BMW X5 / X6 / X7 Belt Slip Fault 21B209

BMW has released Service Information Bulletin SIB 12 07 21, Revision 3, which supersedes the bulletin dated November 2023. This bulletin addresses a specific issue related to the 48V system and the B58C/D engine, leading to a BMW X5 belt slip fault 21B209.

This technical service bulletin provides detailed diagnostic and repair procedures for various 2021-2024 BMW models, including the X5, X6, X7, 3 Series Sedan, 5 Series Sedan, 4 Series Coupe, and 640i xDrive Gran Turismo, all equipped with the B58C/D engine and 48V system.

Symptoms

Owners of affected BMW vehicles may experience a range of symptoms indicating a BMW X5 belt slip fault 21B209. The primary indicators include a Check Control message and the illumination of the Service Engine Soon light. Specific symptoms are:

• A Check Control message displaying: "(ID 213): Stop, exercising due care. Voltage supply"
• The Service Engine Soon light illuminated on the dashboard.
• Noise emanating from the belt drive area.
• An unusual odor from the engine compartment.
• Visible smoke formation around the belt drive.
• The drive belt appearing damaged, prematurely worn, or completely torn.

Fault Codes / DTCs

When diagnosing the issue, the Digital Motor Electronics (DME) system will typically log a specific fault code:

Code	Description	Module
21B209	Starter alternator / belt for 48V system (OSA_RIEMEN_RISS): Belt between Combustion engine and starter generator torn	DME

Diagnosis and Trigger Conditions

The underlying cause of the BMW X5 belt slip fault 21B209 is identified as slipping of the drive belt. This typically occurs under certain operating conditions, specifically during overrun (off-throttle) operation at low engine speeds. Technicians will use the ISTA diagnostic system to confirm the fault code and follow specific test plans related to the fault code and the 48V system.

Part of the diagnostic process involves visually inspecting the belt tensioner. Technicians will check the alignment marks on the tensioner, ensuring the black mark is centered within the adjustment window. This visual check helps confirm proper belt tension and alignment.

Repair Procedure Summary

The repair for the BMW X5 belt slip fault 21B209 involves a detailed inspection and replacement process for the drive belt and related components. The procedure includes:

1. Initial Diagnosis: Performing a full diagnosis using ISTA and following all relevant test plans for the fault code and the 48V system.
2. Belt Tensioner Inspection: Checking the alignment marks on the belt tensioner. As illustrated in the bulletin, a black mark on the tensioner should be centered in its adjustment window.
3. Drive Belt Inspection and Replacement: Removing and visually inspecting the drive belt. Technicians will look for signs of wear on the ribs, cuts, missing ribs, or oil contamination. The ribs may also appear narrower or worn thin. The drive belt will be replaced as part of this repair.
4. Crankshaft Damper Check: Using a mirror to check the index number of the crankshaft damper. If the damper has an index number of 01, it must be replaced.
5. Starter Generator Pulley Inspection: Inspecting the pulley on the starter generator for tightness. The retaining screw for the hexagon nut on the SGR drive pulley is checked. If the screw is loose or missing, the starter generator must be replaced.
6. Pulley Cleaning and Inspection: If the retaining screw is tight, the pulley grooves for the belt material are cleaned using brake cleaner and a cloth rag. Technicians will check that the SGR pulley spins freely and may video any binding observed.
7. Water Pump Pulley Inspection: Checking the water pump pulley for binding and ensuring it spins freely. Any issues with the water pump will lead to its replacement.
8. AC Compressor Pulley Inspection: Checking the AC compressor pulley grooves for belt material and cleaning them. If the AC compressor or its pulley is damaged or leaking, the AC compressor will be replaced.

Required Tools or Parts

The following parts may be required for the repair, depending on the inspection findings. Specific part numbers should be confirmed using the vehicle's chassis number in ETK or AIR systems.

• 11 28 9844643: Ribbed v-belt (6PKx1196 (48V)) (Quantity: 1)
• 11 23 9845162: Vibration Damper (Quantity: 1)
• 11 23 8585220: ASA-Bolt (M10x65) (Quantity: 4)
• 11 11 8664905: Shaft seal (55x68x8) (Quantity: 1)

Important Warnings

This repair, identified by defect code 1128026900 ("Ribbed V-belt, main drive Worn / sheared through"), is covered under the terms of the BMW New Vehicle Limited Warranty for Passenger Cars and Light Trucks. Owners should contact their authorized BMW dealer to schedule an inspection and repair if they experience the symptoms described in this bulletin.

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Source: NHTSA ID: 10252038, SIB 12 07 21