BMW DTC U123D – Lost Communication Slave-ECM With Master-ECM Interconnection 5
DTC U123D meaning on BMW
DTC U123D on a BMW indicates a communication error between the Slave-ECM (Engine Control Module) and the Master-ECM. This error code signifies that the Slave-ECM is unable to establish proper communication with the Master-ECM, which can lead to various issues in the vehicle’s electronic control systems.
BMW DTC U123D symptoms
Symptoms of DTC U123D on a BMW may include:
- Check Engine Light (MIL) illuminated
- Loss of power or performance
- Erratic engine operation
- Difficulty starting the vehicle
- Transmission shifting problems
BMW DTC U123D causes
Common causes of DTC U123D on a BMW include:
- Faulty wiring or connectors in the communication network
- Defective Slave-ECM or Master-ECM
- Interference from other electronic devices
- Software issues in the ECMs
BMW DTC U123D seriousness
The seriousness of DTC U123D on a BMW depends on the extent of the communication failure between the ECMs. Ignoring this error code can lead to further electronic control system malfunctions and potentially affect the vehicle’s drivability and safety.
How to diagnose DTC U123D on BMW
To diagnose DTC U123D on a BMW, a mechanic would typically perform the following steps:
- Use a diagnostic scanner to retrieve the fault codes
- Inspect the wiring and connectors for any visible damage
- Check for proper voltage and ground connections
- Perform communication tests between the ECMs
- Verify software versions and update if necessary
How to fix DTC U123D on BMW
To fix DTC U123D on a BMW, the following steps may be taken:
- Repair or replace any damaged wiring or connectors
- Address any issues with the Slave-ECM or Master-ECM
- Ensure proper communication between the ECMs
- Update software in the ECMs to the latest version
How to erase DTC U123D on BMW
To erase DTC U123D on a BMW, a mechanic can use a diagnostic scanner to clear the fault codes stored in the ECM memory. After fixing the underlying issue causing the error code, the mechanic can then perform a reset to ensure the code does not reappear.
Recommended tools & DTC Scanners for BMW
Best Diagnostic App for modern BMWs: BimmerLink
Recommended Bluetooth adapter for Bimmerlink: OBDLink CX
Cable adapter for Bimmerlink: Enet Cable USB Type C
For older BMWs we recommend: Autel AutoLink AL319 (2024 version)
Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter
Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.