. This is a manufacturer-specific code generated by the Built-in Systems Interface (BSI) when it fails to communicate with or verify the transponder in your key. The Automotive Technician Common Symptoms Intermittent Non-Start : The car may fail to start on the first few attempts. Key Recognition Failure
A low or faulty vehicle battery is the single most common cause of inexplicable B-codes, including B173D. Modern Peugeots are extremely sensitive to voltage drops. When the battery voltage falls below a threshold, the BSI may not have enough power to correctly interpret signals from the key, resulting in a “Fault in identifying” code.
If your diagnostics point to a persistent BSI fault, failed CAN bus communication, or if you lack the tools and expertise, it's time to seek professional help. b173d peugeot
The Peugeot BSI is the brain of the vehicle's cabin electronics, managing everything from central locking to transponder validation.
: Issues with the transponder aerial (the ring around the ignition barrel) or associated wiring can disrupt the signal . Recommended Steps for Resolution Key Recognition Failure A low or faulty vehicle
A weak battery can cause a cascade of phantom codes. Test the battery with a professional battery load tester. If the resting voltage is below or the cranking voltage drops below 9.6V , replace the battery. Even if the battery tests “OK,” any battery older than 4-5 years should be considered suspicious, especially if you’ve experienced unexplained electrical issues.
Let’s move from theory to action. Below is a step-by-step diagnostic and repair approach organized from simplest to most complex. If your diagnostics point to a persistent BSI
Demystifying Peugeot Fault Code B173D: Key, Transponder, and Non-Start Issues Explained
In French and Spanish Peugeot forums, the same code is described as "Défaut d'identification de la clé mécanique/électronique ou de la télécommande" and "Fallo al identificar la llave mecánica/electrónica o el mando a distancia" .
The BSI requires separate power connections to function correctly: one constant battery supply and one ignition-switched supply. If either supply is intermittent (due to a loose connection or faulty relay), the BSI may reset intermittently, losing its ability to identify the key.
As we dig deeper, several theories emerge: