B173d Peugeot
While rare for a single cylinder, some BlueHDi engines have a master fuse for the glow plug control unit. If this fuse blows, you will get multiple glow plug codes for all cylinders (B173C, B173D, B173E, B173F). If you only have B173D, the fuse is fine.
To fix this code, a mechanic or a confident DIYer will typically follow these steps:
Don’t throw parts at the problem. Follow this professional diagnostic flow:
Tools you need: Multimeter, trim removal tool (or small screwdriver), contact cleaner, and ideally a DiagBox or Lexia 3 scanner (basic OBD readers may not read manufacturer-specific B-codes). b173d peugeot
Step 1 – Visual Inspection Locate the air quality sensor. On most Peugeots (308 T9, 208), it is clipped into the front crash bar or behind the lower grille, near the hood latch. Look for physical damage, disconnected wiring, or heavy grime.
Step 2 – Connector Check Unplug the sensor. Inspect the 3 pins. Are they green or white (corrosion)? Spray with electrical contact cleaner. Reconnect and clear the code. Does it return? If not, corrosion was the issue.
Step 3 – Voltage Test (Key ON, Engine OFF) Using your multimeter, probe the wiring harness connector (sensor disconnected): While rare for a single cylinder, some BlueHDi
If power or ground is missing, check fuses and wiring continuity.
Step 4 – Signal Testing (Simulation) Connect the sensor. Back-probe the signal wire. In clean air, the voltage should be around 1.5V to 2.5V. Spray a small amount of cigarette smoke or a solvent-based brake cleaner near the sensor – the voltage should jump to near 5V. If it doesn’t change, the sensor is dead.
The control unit (a small black or silver box mounted on the rocker cover or near the injectors) is a solid-state relay. It can fail for cylinder #4 only. If the MOSFET (transistor) controlling Cylinder 4 burns out, you will get a B173D code even with a perfect glow plug and wiring. If power or ground is missing, check fuses
In Peugeot and Citroën (PSA Group) vehicles, the BSI (Built-in Systems Interface) acts as the vehicle's "brain" or central gateway. It controls the body electronics (lights, locks, wipers, dashboard) and communicates with the Engine ECU and Transmission ECU.
Code B173D indicates a mismatch. Essentially, the Engine ECU (or another module) is saying, "I am sending a message, but the BSI is either not recognizing me, or the BSI is configured for a different version of this car."
This is rarely a broken wire; it is almost always a software or configuration issue.
The sensor receives a 12V or 5V reference from the BSI. A blown fuse in the engine bay fuse box (often F11 or F18, check your manual) can cause this code. Additionally, a BSI that needs a software reset can report false codes.
