BMW 2791 — IBS General
- Severity
- Informational
- Module
- DME
- OBD-II Code
- P150B
Description
Fault code 2791 is a general fault category for the IBS (Intelligent Battery Sensor), covering internal sensor errors and wiring faults on the Terminal 15/wakeup circuit. The IBS uses the Terminal 15 (ignition) signal to determine vehicle operating state — this signal tells the sensor when the car is being driven versus parked, which is critical for accurate charge state tracking and parasitic drain monitoring. Faults in this circuit compromise the entire power management system.
The DME's IBS component driver detected a general error condition. Multiple internal error bits (Ibs_errors bits 3, 4, 5) can trigger this code, covering: internal sensor hardware failure, Terminal 15/wakeup wire faults (short to ground, short to battery voltage, open circuit), and unauthorized wakeup events caused by non-approved electrical devices connected to the Terminal 15 circuit. The fault is confirmed within 2 seconds.
2791 - P150B: IBS General - General sensor / wakeup circuit fault
Symptoms
The driver does not notice this fault directly. No warning lights or CC messages are displayed. However, incorrect Terminal 15 state tracking can cause the IBS to miscalculate parasitic drain — the sensor may think the car is being driven when it is parked (or vice versa), leading to inaccurate battery charge state reporting. This can result in unexpected flat batteries or unnecessary start-stop disabling.
Common Causes
- Terminal 15/wakeup wire fault. The wakeup wire from the IBS runs to the vehicle's Terminal 15 circuit. A short to ground on this wire causes the IBS to receive false ignition-on signals. A short to battery voltage causes constant wakeup. An open circuit prevents the IBS from detecting ignition state changes.
- Non-approved electrical devices on the Terminal 15 circuit. Aftermarket dash cameras, alarm systems, or other accessories hardwired to the ignition circuit can cause spurious wakeup signals that confuse the IBS.
- Internal IBS hardware failure. The sensor's internal processing circuit has failed, requiring replacement.
- Loose or corroded IBS connector. The multi-pin connector at the battery terminal is exposed to harsh conditions.
Diagnosis Steps
- Inspect the IBS connector and wiring harness at the battery. Check for corrosion, damaged pins, and secure seating.
- With the battery sensor disconnected and ignition off, measure the Terminal 15/wakeup wire at the IBS connector for short to ground (should read open) and short to battery voltage (should read 0V). Any voltage present with the ignition off indicates a wiring fault or an aftermarket device backfeeding the circuit.
- Check for aftermarket devices connected to the Terminal 15/wakeup circuit. Dash cameras, aftermarket alarm systems, and GPS trackers are common culprits. Disconnect them and retest.
- Check the Terminal 15/wakeup wire for open circuits and intermittent connections by measuring continuity while flexing the wire along its routing path.
- With the sensor removed and Terminal 15 off, check the Terminal 15/wakeup wire for short to battery voltage. If voltage is present, trace the wire to identify the source — another control module or aftermarket device may be driving the line high.
- If all wiring checks pass and no aftermarket devices are found, the IBS has an internal hardware failure and requires replacement.
Resolution
Repair any wiring faults found on the Terminal 15/wakeup circuit. Remove or properly isolate any non-approved aftermarket devices from the Terminal 15 circuit. If the IBS has an internal failure, replace the battery sensor. After replacement, clear the fault code and allow several drive cycles for recalibration. No coding or programming required.