About this replacement
VOLVO S60 CC / S80 II / V40 CC Series — 4V HPC 600F Replacement Supercapacitor (31350776)
This is a 4V, 600F (2.4Wh) high-power-capacitance supercapacitor that replaces the OEM siren alarm backup unit in VOLVO S60 CC (2016–2018), S60 II (2014–2018), S80 II (2007–2016), V40 CC (2016–2019), and seven additional model variants. It holds charge to power the vehicle's siren alarm during a main battery disconnection or power loss event. When this unit degrades, the alarm system logs warnings and the siren may fail to activate.
- Multi-model siren platform fit: The listed VOLVO models share the same 4V siren sounder architecture, the same physical connector, and the same BMS handshake protocol — which is why one part number (31350776) spans the full range. The siren module draws from this capacitor only when the vehicle's 12V supply is interrupted, so the BMS must confirm adequate stored energy before clearing the alarm-ready status.
- Bench tested on actual hardware: We cycled this supercapacitor through repeated charge and discharge sequences, confirming the BMS accepts the unit without fault codes and that the capacitor reaches full charge state within the vehicle's siren module charge window. No BMS rejection or communication errors were observed during testing.
- Post-installation siren cover check: After swapping this unit into the siren housing, confirm the siren cover is fully latched and the tamper switch is physically engaged before closing the vehicle up. VOLVO's alarm control unit treats an open tamper switch as a fault condition — and on some builds, that fault is misread by the panel as a capacitor error rather than a cover issue.
Why the VOLVO siren alarm logs a capacitor fault even after fitting a new unit
Supercapacitors need time to reach their rated charge state after installation. The VOLVO siren module continuously monitors stored energy and will hold a fault flag if the capacitor reads below its minimum activation threshold. This is normal immediately after fitting — it is not a sign of a faulty unit. The module typically clears the fault once the capacitor has been trickle-charged by the vehicle's siren circuit for a full 24-hour period with the vehicle in its normal armed state. If the fault persists beyond 24 hours, check the connector seating and verify terminal voltage is at or near 4V with a multimeter.
Siren sounds briefly then cuts out during an alarm trigger
This symptom points to a capacitor that cannot sustain the siren's output current draw for the full activation cycle. A supercapacitor in this application discharges rapidly under the siren's peak current load — if the unit has degraded or was not fully charged before the trigger, voltage collapses mid-cycle and the siren cuts out. The VOLVO siren module interprets this as a loss of supply and silences the sounder. To rule out a charge-state issue rather than a failed unit, allow 48 hours of charge time after installation, then retest — a healthy unit at full charge should hold above 3.5V under siren load.