B173d Peugeot Now

Before spending money on parts, try resetting the BSI properly.

Use a diagnostic tool (such as Diagbox,

The fault code B173D in Peugeot and Citroën vehicles is a diagnostic trouble code (DTC) typically related to the immobilizer system or key recognition . What the Code B173D Means

This code indicates that the vehicle's electronic control unit (ECU) or Built-in Systems Interface (BSI) is having trouble communicating with the key . Common symptoms include:

"Key not detected" or "Immobilizer fault" warnings on the dashboard .

The engine failing to start or cutting out shortly after starting . Central locking malfunctions . Common Causes

Weak Key Fob Battery: A low battery in the remote can prevent the immobilizer signal from being read correctly . b173d peugeot

Vehicle Battery Issues: In Peugeot models (like the 308 or 5008), an old or undercharged car battery can cause the BSI to throw multiple "ghost" codes, including B173D, as it tries to conserve power .

BPGA Module Failure: The Battery Power Supply Protection and Management Unit (BPGA), located near the battery, is a frequent failure point in modern Peugeots that leads to electrical and starting faults .

Antenna or Wiring Faults: Issues with the transponder aerial (the ring around the ignition barrel) or associated wiring can disrupt the signal . Recommended Steps for Resolution

Step 1: Check the Key: Replace the key fob battery first. If you have a spare key, try using it to rule out a faulty transponder in the primary key .

Step 2: Test the Main Battery: Have the car’s main battery health tested. If it is weak, replacing it with the correct AGM type (especially for Stop/Start models) often clears the code automatically after a short drive .

Step 3: Inspect the BPGA: Check for corrosion or damage to the unit attached to the front or top of the battery . Before spending money on parts, try resetting the

Step 4: Diagnostic Scan: Use a dedicated diagnostic tool like Diagbox to read the specific BSI logs and clear the codes once the hardware issue is fixed . AI responses may include mistakes. Learn more

Once you have diagnosed the faulty component, here is the repair path.

Q: Can I drive my Peugeot with code b173d? A: Yes, it is safe to drive. Your engine and brakes are unaffected. However, you will lose automatic air recirculation, meaning more external pollution enters the cabin. You can still manually press the recirculation button.

Q: Will b173d fail a safety inspection (MOT / TÜV / Smog)? A: In most regions, a body code (B-code) will not cause an automatic emissions failure, because it’s not an engine (P-code) fault. However, if the check engine light is illuminated, some inspection stations may fail you depending on local laws. Always clear the code before an inspection.

Q: My scanner won’t read b173d – why? A: Generic OBD2 scanners only read engine and transmission codes (P0700 series). You need a PSA-specific scanner (Lexia 3, DiagBox, or high-end Autel/Mac Tools) that can communicate with the BSI module.

Q: I replaced the sensor, but the code came back. What now? A: Check the wiring harness for a short to ground. Also, ensure you bought the correct sensor. Some Peugeots have different sensors for dual-zone vs. manual A/C. Finally, perform a BSI hard reset (disconnect battery for 30 minutes, touch leads together, then reconnect). The B173D code specifically points to an electrical

This is the #1 cause of B173D in Peugeots. If the battery was disconnected or replaced recently without following the correct "Sleep Mode" procedure, the BSI can lose its configuration or corrupt the data handshake with other modules.

To understand this fault, you must first forget everything you know about old diesel engines.

The Old Way: In older diesels, glow plugs only activated for 10–30 seconds before starting the engine to heat the combustion chamber. Once the engine was running, the glow plugs turned off.

The New Way (BlueHDi): Modern Peugeot engines (DV6 and DW10 BlueHDi) use a "Glow Plug Control Unit" that keeps the glow plugs active for up to 3 to 4 minutes after the engine starts. They assist with:

The B173D code specifically points to an electrical open circuit or a resistance issue on the 4th cylinder (the cylinder closest to the timing belt or flywheel, depending on engine orientation). "Open circuit" means the engine control unit (ECU) tried to send voltage to that glow plug, but the electrical loop was broken.