U0120 – BMW DTC

BMW DTC U0120 – Lost Communication With Starter/Generator Control Module

DTC U0120 meaning on BMW

DTC U0120 on a BMW indicates a communication error between the Engine Control Module (ECM) and the Starter/Generator Control Module. This error code signifies that the ECM is unable to establish communication with the Starter/Generator Control Module, which can lead to issues with starting the vehicle or controlling the generator functions.

BMW DTC U0120 symptoms

Symptoms of DTC U0120 on a BMW may include:

• Difficulty starting the vehicle
• Engine stalling or not starting at all
• Loss of power steering assistance
• Malfunction indicator light (MIL) illuminated on the dashboard

BMW DTC U0120 causes

The common causes of DTC U0120 on a BMW include:

• Faulty Starter/Generator Control Module
• Wiring or connection issues between the ECM and Starter/Generator Control Module
• Low battery voltage
• Software glitches in the control modules

BMW DTC U0120 seriousness

The seriousness of DTC U0120 on a BMW depends on the extent of the communication failure between the ECM and the Starter/Generator Control Module. Ignoring this issue can lead to starting problems, potential engine stalling, and overall drivability issues. It is recommended to address this error code promptly to avoid further complications.

How to diagnose DTC U0120 on BMW

To diagnose DTC U0120 on a BMW, follow these steps:

1. Use a diagnostic scanner to retrieve the fault codes stored in the ECM.
2. Check the wiring and connections between the ECM and Starter/Generator Control Module for any visible damage or loose connections.
3. Test the battery voltage to ensure it is within the proper range.
4. Perform a communication test between the control modules using diagnostic tools to identify the source of the communication error.

How to fix DTC U0120 on BMW

To fix DTC U0120 on a BMW, consider the following solutions:

• Inspect and repair any damaged wiring or connections between the ECM and Starter/Generator Control Module.
• Replace the faulty Starter/Generator Control Module if necessary.
• Update the software in the control modules to address any glitches causing the communication error.
• Clear the fault codes using a diagnostic scanner after completing the repairs.

How to erase DTC U0120 on BMW

To erase DTC U0120 on a BMW, follow these steps:

1. Connect a diagnostic scanner to the vehicle’s OBD-II port.
2. Select the ¨Erase Codes¨ or ¨Clear Codes¨ function on the scanner.
3. Follow the on-screen prompts to confirm the deletion of the fault codes.
4. Once the DTC U0120 code is successfully cleared, verify that the MIL light is no longer illuminated.

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

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