Troubleshooting BMW U0079 Code After Battery Replacement

Experiencing a U0079 fault code in your BMW after a battery change can be frustrating. This article provides expert guidance, drawing from real-world experience, to help you resolve this issue effectively. If you’ve just replaced your BMW’s battery and are now facing the U0079 code, often associated with communication issues, you’re in the right place. Let’s dive into proven methods to get your BMW back to optimal performance.

Method 1: The Battery Disconnect and Reconnect Reset

Sometimes, a simple yet effective solution involves a complete power cycle of your BMW’s electrical system. This method is particularly useful after battery replacements, as it allows the car’s computer systems to reset and properly recognize the new power source.

Here’s how to perform a battery disconnect reset:

1. Disconnect the Battery: Completely disconnect your BMW’s battery. Ensure both the negative and positive terminals are detached.
2. Wait for at Least 6 Hours: This extended disconnection period is crucial. It allows sufficient time for any residual electrical charge to dissipate, ensuring a thorough system reset. In practice, leaving it disconnected overnight is a reliable approach.
3. Reconnect and Rescan: After the waiting period, reconnect your brand new battery securely. Start your BMW and use an OBD scanner to rescan for fault codes. Note down any codes that appear.
4. Clear Fault Codes: Following your OBD scanner’s instructions, clear all fault codes.
5. Post-Clearance Procedure: Turn off your car, remove the key, and lock the vehicle. Let your BMW sit undisturbed for about 30 minutes.
6. Driving Cycle for IM Readiness: After the rest period, get back in your BMW and drive it. To ensure your BMW’s systems are fully recalibrated, you’ll need to complete a driving cycle until the IM (Inspection/Maintenance) readiness monitors are set. This often requires driving for at least 25 miles in one direction and then returning, totaling 50+ miles. This driving cycle helps the car’s computer relearn and adapt to the new battery and clear any lingering issues related to the Cd8e10 system if it is related to communication or power management.

This method addresses potential communication glitches that can arise after battery changes and is a good starting point for resolving the U0079 code.

Method 2: Utilizing ISTA+ for ECU Reset

For BMW owners who have access to ISTA+ (Integrated Service Technical Application), a more advanced diagnostic and programming tool, an ECU reset can be a targeted solution. This method is particularly helpful for more persistent U0079 errors or for those familiar with using ISTA+.

Here’s how to use ISTA+ for an ECU reset:

1. ISTA+ Scan: Run a full vehicle scan using ISTA+. Observe the ECU modules displayed; they might be highlighted in yellow, green, or red, indicating their status.
2. Identify Battery-Related ECU: Locate the ECU module that is likely associated with the battery or power management system. In some BMW models, this might be labeled STMR or similar. Note: The exact label can vary depending on your BMW model and year.
3. “Call Up ECU” Function: Select the identified ECU module. In the bottom left corner of ISTA+, you’ll find the “Call Up ECU” option. Click on this.
4. Navigate to “Reset ECU” Tab: Within the ECU function menu, look for a tab labeled “Reset ECU”. Select this tab.
5. Trigger ECU Reset: Ensure “Reset ECU” is selected within the tab. Then, in the bottom right of the ISTA+ interface, click the “Trigger” button to initiate the ECU reset process.
6. “Undo All” and Exit: After the reset is triggered, click “Undo All” in the bottom left corner, then close the ECU function window.
7. Fault Code Deletion: Return to the main ISTA+ screen and delete all fault codes. Exit the ISTA+ program.

Important Note on ECU Reset and Adaptation: Resetting the ECU doesn’t instantly clear the U0079 code. Patience is key. After the reset, drive your BMW normally over the next day or two. This allows the car’s computer to relearn and store your driving profile with the new battery and power conditions. With a new, fully functional battery providing sufficient amperage, the system should adapt and resolve the error.

Recommendation: After 24 to 72 hours (2-3 days) of normal driving following the ECU reset, rescan your BMW with an OBD scanner or ISTA+ to check if the U0079 code has been cleared and that all systems are functioning correctly.

Conclusion: Resolving Your BMW U0079 Code

These methods offer practical steps to address the U0079 code in your BMW after a battery replacement. Starting with the battery disconnect method is a straightforward first step. If the issue persists, utilizing ISTA+ for an ECU reset provides a more targeted approach. Remember that allowing the car’s computer time to relearn and adapt after these procedures is crucial for success.

These solutions have proven effective in resolving similar issues in various BMW models, including the 2006 750i, 2006 M5, 2013 750li, and 2016 4 series. By following these expert tips, you can confidently tackle the U0079 code and ensure your BMW operates smoothly after a battery change. Good luck, and we hope this helps your fellow BMW enthusiasts!