9C71

What the code means

Code 9C71 (left side) or 9C72 (right side) is logged by the light control module (LCM) when it detects resistance that's too low in the exterior lighting circuit. The cause is fitting LED modules in place of the stock incandescent bulbs: LEDs draw far less current than the original bulbs, and the LCM reads that as a fault (open circuit or short).

The LCM monitors current in the circuit and sets the fault when it goes outside the allowed range. Stock bulbs have a specific resistance the controller expects to see; LED modules without extra load (resistors) don't draw the required current, which is what triggers code 9C71 (or 9C72 on the right side).

Symptoms

• An error message in iDrive with code 9C71 — “Exterior lighting fault.”
• Code 9C72 may also show up when the fault is on the right side.
• The lights may work visually, but the LCM still logs a current mismatch.

Diagnosis and repair

1. Check the bulbs fitted: make sure the headlights/tail lights use stock incandescent bulbs or LED modules with the correct resistance.
2. Fit resistors: to clear 9C71 (and 9C72), use resistors together with the LED modules. That raises current draw to the level the LCM reads as normal.
3. Choose LED modules with built-in resistors: kits such as Morimoto XB or Spec-D Tune are preferable since they don't need wiring work.
4. Alternative: consider fitting original BMW light units that work with iDrive without errors (for pre-LCI models).

Tools: diagnosing may require ISTA or INPA to read codes and check LCM parameters.