U123C – BMW DTC

BMW DTC U123C – Message Monitoring Slave-ECM with Master-ECM Interconnection 5 Alive Check

DTC U123C meaning on BMW

The DTC U123C code on a BMW refers to the Message Monitoring Slave-ECM with Master-ECM Interconnection 5 Alive Check. This code indicates a communication issue between the slave Engine Control Module (ECM) and the master ECM in the vehicle’s network.

BMW DTC U123C symptoms

Symptoms of the DTC U123C code on a BMW may include:

• Check Engine Light (MIL) illuminated
• Communication error messages on the vehicle’s display
• Performance issues such as rough idling or poor acceleration

BMW DTC U123C causes

Common causes of the DTC U123C code on a BMW include:

• Faulty ECM software
• Wiring or connection issues in the communication network
• Defective ECM hardware

BMW DTC U123C seriousness

The DTC U123C code should be addressed promptly as it can lead to communication breakdowns between critical control modules in the vehicle. Ignoring this code may result in drivability issues and potential safety concerns.

How to diagnose DTC U123C on BMW

To diagnose the DTC U123C code on a BMW, a mechanic would typically perform the following steps:

1. Use a diagnostic scanner to retrieve the fault codes stored in the vehicle’s ECM
2. Inspect the wiring and connectors related to the ECM communication network
3. Check for any software updates or reprogramming available for the ECM

How to fix DTC U123C on BMW

To fix the DTC U123C code on a BMW, the following steps may be taken:

1. Address any wiring or connection issues in the ECM communication network
2. Update the ECM software to the latest version, if available
3. If necessary, replace the faulty ECM with a new or remanufactured unit

How to erase DTC U123C on BMW

To erase the DTC U123C code 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 code, the mechanic can then perform a relearn procedure to ensure proper communication between the ECMs.

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.