Battery State of Charge Estimation Degraded
What does TESLA-BMS_A116 mean?
The TESLA-BMS_A116 (Tesla BMS (Battery Management System)) EV fault code means: Battery State of Charge Estimation Degraded. This is a moderate severity code.
Common Symptoms
- Displayed range jumps or drops unexpectedly during driving
- Estimated miles remaining does not match actual driving behavior
- Charge percentage shown on touchscreen fluctuates without a clear cause
- Energy graph in the Tesla app shows erratic consumption patterns
- Car reaches a low state of charge warning sooner than expected based on displayed percentage
- Charging session ends early or does not reach the set limit consistently
- BMS_a116 alert visible in service menu or via Scan My Tesla app with OBDLink MX+ or Veepeak adapter
Probable Causes (Ranked by Likelihood)
- Battery pack has not completed a full calibration cycle in a long time, causing SOC algorithm drift Very Likely
- Cells within the pack have significantly uneven state of charge due to imbalance, confusing the BMS estimation model Very Likely
- Degraded cell capacity that no longer matches the BMS internal capacity model, leading to inaccurate coulomb counting Likely
- Intermittent CAN communication fault between the BMS controller and individual cell monitoring boards inside the pack Possible
- Software bug or incomplete BMS firmware update that corrupted stored calibration data Possible
- Temperature extremes (very cold or very hot ambient conditions) causing temporary cell voltage behavior that throws off SOC modeling Possible
- Physical damage or moisture intrusion in the HV battery pack affecting cell monitoring circuits Less Likely
Step-by-Step Diagnostic Procedure
Start by pulling the full fault log. Use Scan My Tesla app with an OBDLink MX+ or Veepeak adapter plugged into the OBD port. Navigate to BMS faults and record all active and historical codes alongside BMS_a116. Note whether any BMS_f or BMS_w codes are present, which would indicate a more serious underlying fault.
Check your recent charging history in the Tesla app. Look for patterns where the car consistently stops short of your set charge limit or where the displayed percentage seems to jump. This helps confirm whether the SOC error is new or has been building over time.
Inspect the battery pack exterior for any signs of physical damage, water intrusion, or collision impact. Look underneath the car with a flashlight. Any visible deformation or discoloration near the pack is a reason to stop and call a Tesla-authorized shop before driving further.
Perform a BMS recalibration cycle. Charge the car slowly on a Level 1 (120V) or Level 2 (240V) home charger, not Supercharger, to 100 percent. Let it reach 100 percent and hold the charge for at least one additional hour if your charger allows it. Then drive the car in normal conditions down to 10 to 20 percent state of charge without using regenerative braking in a way that masks the discharge. Repeat this cycle once or twice. This gives the BMS enough data to re-anchor its coulomb-counting algorithm.
After the recalibration cycle, check whether the range estimate stabilizes. If the displayed percentage still jumps erratically or the fault returns within a few charge cycles, the issue is more likely hardware-based (cell imbalance or degraded cells) rather than a software drift issue.
Check cell balance data if your OBD adapter and Scan My Tesla app support it. Look for individual cell voltages that deviate more than 50 to 100 mV from the pack average while at rest. A large spread indicates cell imbalance that the BMS passive balancing system may not be able to correct on its own.
If the code persists after two full recalibration cycles and cell voltages look uneven, the pack likely needs evaluation by a Tesla service center or an independent EV shop with Tesla Toolbox 3 access. Toolbox 3 can force a full BMS re-learn and read raw cell-level data that consumer OBD tools cannot access.
Frequently Asked Questions
What does Tesla code BMS_a116 mean?
It means the BMS, the controller that tracks your battery state of charge, has lost confidence in its own math. The percentage and range estimate you see on the touchscreen are calculated by the BMS using a mix of cell voltages, current flow, and a stored capacity model. When that model drifts out of sync with real-world cell behavior, the BMS flags BMS_a116 to tell you the number you see may not be accurate.
Can I still drive my Tesla with BMS_a116 active?
Yes, but with caution. The car will still drive normally in most cases. The risk is that the displayed state of charge may not accurately reflect how much energy is actually available, so you could run out of charge sooner than expected. Avoid long trips to the edge of your estimated range until the fault is resolved or the BMS is recalibrated.
How much does it cost to fix BMS_a116?
If a recalibration cycle fixes it, the cost is zero. If you need a service visit, independent EV shops typically charge $150 to $300 for diagnostics. BMS firmware updates are usually under $200 at a Tesla service center. If the root cause is significant cell degradation or a failed cell monitoring board inside the pack, repair costs climb quickly into the $1,500 to $6,000+ range depending on what needs replacing.
Will doing a full charge to 100 percent fix this code?
It often does, especially if the BMS simply has not seen a full charge-to-discharge cycle in a long time. Charging slowly to 100 percent on a Level 1 or Level 2 charger, letting it sit at 100 percent for an hour, then driving down to around 10 to 20 percent gives the BMS the data it needs to recalibrate its internal model. Do this one or two times before assuming a hardware fix is needed.