how to troubleshoot U0121 code in Ram 1500 DT (2019-Present)?

Learn how to troubleshoot and fix U0121 communication issues in Ram 1500 DT. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Ensure that the vehicle is on a level surface and safely supported.

2. Inspect and Test Fuses

• Locate the fuse box and identify the fuses associated with the BCM and other modules.
• Remove each fuse and visually inspect for any blown fuses.
• Replace any blown fuses with the same amperage rating.
• Reconnect the battery and check if the error code persists.

3. Check Wiring and Connectors

• Remove the BCM connector and inspect for bent pins or corrosion.
• Use a multimeter to check for continuity in the wiring harness between the BCM and other modules.
• Repair or replace any damaged wires or connectors as necessary.

4. Test BCM Functionality

• Reconnect the BCM connector and ensure it is securely fastened.
• Use an OBD-II scanner to clear the U0121 code and check for any new codes.
• Perform a functional test of the BCM and related systems. If the U0121 reappears, consider replacing the BCM.

5. Replace the BCM (if necessary)

• If the BCM is determined to be faulty, disconnect the battery again.
• Remove the BCM from its mounting location, taking care to note the orientation and connections.
• Install the new BCM and reconnect all connectors.
• Reconnect the battery and perform a system scan to ensure the installation was successful.