Is the footwell module (FRM) of the BMW series:
- E70
- E7
- E8
- E8
- E87
- E90
- E91
- E92
- E93
- as well as in the Mini R56
If the error code “9CBB – Short circuit error” is stored, this means that the internal error counter has run high.
The error code is related to a malfunctioning exterior light bulb. The cause is either a short circuit in the cable connection or a defective light bulb that has been defective for some time.
Further errors relating to defective light bulbs or short circuit errors in the affected power circuits are stored in the error memory. The malfunction is shown in the driver information display.
System description
The central electronics (FRM) in BMW vehicles are responsible for distributing power in the on-board electrical system. All exterior lighting functions are integrated into this system, as well as control of the front doors with window regulators and the exterior mirrors. The circuits are fused upstream of the central electronics (FRM) at the input. The voltage can also be switched by relays before the control unit. The function of the central electronics system includes monitoring all directly connected components and exchanging information via CAN with control units such as the DSC, CAS, and junction box electronics (JBE). The central electronics system thus simultaneously performs complex control tasks and diagnostic processes for the connected components and their functions.
Function description: Error code “9CBB – Short circuit error”
The central electronics (FRM) continuously monitor all outputs to alert the driver to any lighting malfunctions. With each ignition cycle, the system runs a test routine that performs a cold diagnosis of the current paths and light sources. If a defect is detected, the short-circuit counter for the respective output/lamp is incremented with each ignition change. The counter is incremented each time until the fault is rectified. The protective circuit in the central electronics is active and suppresses the control of the current path to prevent consequential damage. When the value reaches 60, monitoring ends and the protective circuit remains permanently active. The fault cannot then be cleared.
Consequences of the error
The affected power path is temporarily deactivated in the central electronics. To protect the control unit hardware from the consequences of permanent overload, the function is blocked by a frequency logic.
Diagnosis/measurements/repair
It is essential to differentiate between the following two types of errors.
A: Defective light source
If the lamp is replaced before the counter starts running…
- If the replacement is carried out with the ignition switched on and the lights switched on, the protective circuit is still active and the lamp remains off. After switching the ignition, the function is restored. The error message on the display disappears. The error in the memory and the counter are automatically deleted.
- If the light bulb is replaced with the ignition off and the lights on, the deletion process and restoration of function will take place after the ignition is switched on, as described above.
If the light source is replaced after the meter has started up…
- The lamp does not light up. There is no permanent control from the central electronics (FRM).
- Actuator test with diagnostic tool is possible. The light source is controlled for a test sequence.
B: Short-circuit fault
One of the exterior lighting bulbs is not working. The bulb is not faulty. Fault in the cable harness to the bulb. Short circuit to ground.
- The protective circuit is active in the event of a short circuit. Unlike a bulb fault, the error message includes the message “Short circuit” and the component. The counter counts up to 60 with each ignition cycle.
- Once the counter has exceeded the value 60, the error message “9CBB – Short circuit error” appears in addition to the original error.
- Actuator test with diagnostic tool is possible. However, the light source is not activated. The counter cannot be read with the diagnosis.
- After successful troubleshooting and correct repair of the cable, the intact light source still does not function. A measurement in the current path confirms that the FRM is not activating it.
Since the error counter has run up, the current path remains permanently switched off. Only when the FRM is repaired is the counter reset and the function restored.
All faults must be rectified before installing a new or repaired central electronics unit (FRM), as the counter will run up again with each ignition cycle.
Damage to control units with repair option related to error code “9CBB – short circuit error” following brands:
BMW repair
BMW Footwell Module (FRM) / Light Control Unit
Mini repair
Mini footwell module (FRM) / light control unit
