Avoid aftermarket BPGA units. PSA proprietary parts are required for CAN bus communication. A cheap clone may work for a week, then fail with the same B173D code.

Intermittent limp mode, B173D stored. Attempted fix (outside garage): New battery, new glow plugs – no change. Our diagnosis: Measured relay coil resistance – open circuit. Replaced pre-heat relay ($35). B173D returned after 3 days. Root cause: Relay socket corrosion caused heat damage to the new relay. Final work: Replaced entire BPGA unit and both relays. Executed BMS reset. Result: 6 months, 8,000 miles – no reoccurrence.

The system may refuse to engage or suddenly "gap" out.

: Many Peugeot owners resolve "ghost" codes by resetting the BSI. According to Peugeot community guides, a common procedure involves: Disconnecting the battery for several minutes.