BMW fault 286A - Valvetronic servomotor (power supply)
P1055 · Supply voltage circuit high
286A indicates that the supply voltage to the Valvetronic actuator motor on bank 1 is higher than the allowed operating range. This is an over-voltage fault that typically points to an electrical system issue rather than a Valvetronic component failure.
The monitoring runs with the engine running, main relay on, the Valvetronic relief relay not commanded, and after a sufficient downtime and post-start delay. Battery voltage must be above 10 V. The code triggers when the supply voltage at the Valvetronic output stage exceeds the upper threshold.
- Module
- DME
- Severity
- Warning
- Likely cause
- Alternator overcharging or external over-voltage event
- Common fix
- Correcting the charging system or clearing after a one-time event
Symptoms
- No warning lights in most cases.
- Often appears alongside other over-voltage faults across multiple modules.
- Rough running or reduced power if the DME enters a protective mode.
- Frequently logged after a jump-start or charging system fault.
Common causes
- Alternator voltage regulator overcharging. A healthy charging system should hold roughly 13.8-14.8 V at the battery with the engine running.
- Vehicle jump-started from a 24 V source (truck battery) or connected to one for too long.
- External battery charger or boost pack operated in the wrong voltage mode.
- Wiring fault or corrosion in the Valvetronic supply circuit or relief relay presenting an out-of-range voltage.
- Failed battery sensor or incorrect battery registration after replacement causing charging system anomalies.
Diagnosis
- Read fault memory across all modules with ISTA or a compatible scan tool. Over- voltage events typically leave matching high-voltage codes in multiple modules with similar timestamps.
- Measure battery voltage with the engine off (target 12.4-12.8 V) and with the engine running at idle and at 2,000 RPM (target 13.8-14.8 V). Readings consistently above 15 V confirm an overcharging alternator.
- Inspect the main battery cables and ground straps for corrosion, heat damage, or loose connections.
- Inspect the Valvetronic relay, its wiring, and the actuator motor connectors for damage or corrosion.
- If the charging system is healthy and the fault was triggered by a one-time event (jump-start, external charger), clear the code and monitor. It often does not return.
Resolution
Correct the underlying electrical system cause. If the alternator is overcharging, replace it. If the fault was triggered by a one-time event like a jump-start, clearing the code is sufficient. After any battery replacement, register it through ISTA to prevent charging system anomalies.