Customer Complaint
Vehicle intermittently refuses to crank after sitting overnight. Starter engages on subsequent attempts.
System Theory
On G30 platforms, the Intelligent Battery Sensor (IBS) monitors voltage and authorizes cranking via CAS. Voltage below ~10.5 V prevents starter engagement and can trigger secondary valvetronic faults.
Diagnostic Testing
- Resting voltage: 12.1 V
- Load test: dropped to 9.4 V → failed
- Multiple low-voltage faults + valvetronic servo errors
Root Cause
Original AGM battery had high internal resistance → voltage sag → IBS denied crank → secondary valvetronic faults.
Repair Procedure
- Replaced with new OEM AGM 92 Ah battery
- Performed battery registration in ISTA
- Cleared faults and ran valvetronic adaptation
- Road tested 48 hrs – fixed
Parts Used
| Description | Part Number | Qty | Price |
|---|---|---|---|
| Battery – AGM 92 Ah | 61 21 6 902 593 | 1 | $428.00 |
| Labor | — | 2.8 hrs | $420.00 |
Key Lessons
- Low voltage is the #1 cause of ghost valvetronic faults on BMWs
- Always load-test the battery
- Battery registration is mandatory
Submitted by: Alex Rivera – Master Technician, Munich West BMW