U0021 – BMW DTC

BMW DTC U0021 – Low Speed CAN Communication Bus (+) Open

DTC U0021 meaning on BMW

The DTC U0021 error code on a BMW indicates a Low Speed CAN Communication Bus (+) Open fault. This means that there is an issue with the communication bus circuit on the vehicle, specifically related to the positive side of the low-speed Controller Area Network (CAN) bus.

BMW DTC U0021 symptoms

Symptoms of the BMW DTC U0021 code may include:

• Malfunction indicator light (MIL) or check engine light illuminated on the dashboard
• Problems with various vehicle systems such as ABS, traction control, or stability control
• Loss of communication with certain control modules

BMW DTC U0021 causes

Common causes of the BMW DTC U0021 error code include:

• Wiring harness issues such as open circuits or shorts
• Faulty CAN bus module or control module
• Corrosion or poor connections in the wiring harness

BMW DTC U0021 seriousness

The DTC U0021 error code should be addressed promptly as it can affect the proper functioning of various vehicle systems that rely on the CAN bus communication. Ignoring this issue may lead to further complications and potential safety hazards while driving.

How to diagnose DTC U0021 on BMW

To diagnose the DTC U0021 code on a BMW, you can follow these steps:

1. Use a diagnostic scanner to retrieve the fault codes stored in the vehicle’s computer
2. Inspect the wiring harness for any visible damage, corrosion, or loose connections
3. Check the CAN bus module and related control modules for proper operation
4. Perform a continuity test on the CAN bus circuits to identify any open circuits

How to fix DTC U0021 on BMW

To fix the DTC U0021 error code on a BMW, you can try the following solutions:

1. Repair or replace any damaged wiring harness or connectors
2. Replace the faulty CAN bus module or control module if necessary
3. Clean any corrosion from the wiring harness connections
4. Clear the fault codes using a diagnostic scanner after completing the repairs

How to erase DTC U0021 on BMW

To erase the DTC U0021 error code on a BMW, you can use a diagnostic scanner to clear the fault codes stored in the vehicle’s computer. After addressing the underlying issue causing the fault code and making the necessary repairs, you can reset the system by erasing the code. This should turn off the malfunction indicator light on the dashboard.

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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