A completely dead battery on a 2010 Peugeot 308 with a P1676 code usually points straight to the alternator, but the BSS network changes the diagnostic path. A workshop in Hungary recently ran this exact scenario through the diagnostic platform we build. The technician noted the battery was completely dead ("Akku teljesen lemerült") and pulled P1676, which flags an incorrect value received on the BSS network from the controlled alternator.
Tracing the BSS Communication Line
When the Engine Control Unit cannot talk to the alternator over the Bit Serial Synchronous (BSS) network, it cannot send charging requests. The alternator then defaults to a low-output mode or stops charging entirely. This leaves the vehicle running strictly on battery power until it discharges.
Our platform ranked an alternator BSS communication wiring fault as the most likely culprit at 90 percent. Specifically, this means investigating wire 1085 routing from the ECU to the alternator. On the EP6 engine series, this signal wire is prone to chafing near the engine block. Corroded terminals are also a frequent failure point. The recommended diagnostic path starts with a visual inspection of the wiring harness, followed by a continuity test and a short-to-ground or short-to-power test on the BSS signal wire.
Ruling Out the Internal Voltage Regulator
If the communication wiring is intact, the focus shifts to the alternator itself. We ranked a faulty alternator, specifically an internal voltage regulator or BSS communication circuit failure, at 80 percent.
The voltage regulator generates the charging voltage and communicates its status back to the ECU via the BSS line. An internal failure here means the alternator cannot produce enough voltage to charge the battery, or its communication circuit has dropped offline. This triggers the P1676 code and the resulting no-start condition. To verify this, a technician needs to perform a main output voltage test on the alternator and a BSS signal line disconnect test.
Checking the Battery Monitoring Unit
Modern charging systems rely heavily on accurate battery data. We ranked a faulty Battery Monitoring Unit (BMU) at 60 percent for this code.
Located on the negative battery terminal, the BMU tracks the state of charge and temperature, sending this information directly to the ECU. If this unit is faulty, disconnected, or transmitting incorrect data, the ECU can misinterpret the battery health and command the alternator to stop charging. The battery and alternator might be in perfect condition, but a bad BMU will still cause a progressive battery discharge. The tests for this involve a visual inspection of the BMU connection and monitoring the BMU live data through a scan tool.
Inspecting Ground Connections
Finally, poor battery ground connections came in at a 40 percent probability. The Peugeot 308 (T7) typically has two main battery earth points. One is located on the gearbox and the other on the car body.
Corrosion, loose bolts, or high resistance at these points restrict current flow from the alternator. This causes voltage drops across the electrical system and can interfere with sensitive communication signals like the BSS line. That interference indirectly triggers the P1676 code. A visual inspection of the battery terminals and ground straps, paired with a voltage drop test on the main battery ground cables, will confirm or eliminate this cause.
Next Steps in the Bay
A dead battery and an alternator code tempt a quick parts swap, but a BSS network fault requires confirming the communication lines first. Checking wire 1085 on the EP6 engine takes less effort than replacing a perfectly good alternator. Let me know if you are seeing similar chafing issues on the signal wires for this engine series in your own bays.