Charge Rate Reduced Due to Pack Temperature

Common Symptoms

• Charging speed drops noticeably on a Level 2 home charger, especially on cold mornings
• Touchscreen charge screen shows a lower-than-expected miles-per-hour rate during charging
• Estimated charge completion time is longer than usual for the same state of charge
• Scan My Tesla or TM-Spy shows BMS_w044 logged as an active or recent warning
• Pack inlet temperature readings are below roughly 50 degrees F or above 100 degrees F
• Charge rate climbs back toward normal on its own as the pack warms up during the session
• No warning light or alert appears on the touchscreen in most cases -- code is silent to the driver

Probable Causes (Ranked by Likelihood)

• Cold battery pack below optimal charging temperature, typically below 50 degrees F, slowing lithium-ion intercalation and triggering BMS thermal protection Very Likely
• Vehicle parked outdoors overnight in freezing or near-freezing conditions without preconditioning before the charge session begins Very Likely
• Hot battery pack above roughly 100 degrees F, often after a long highway drive immediately followed by plugging in, causing BMS to throttle charge rate to protect cells Likely
• Thermal management system slow to bring coolant loop up to target temperature because cabin preconditioning was not scheduled or the battery heater draw is competing with charge current Likely
• Degraded or aging battery cells with increased internal resistance that generate more heat per amp, causing BMS to limit rate earlier than on a new pack Possible
• Coolant level low or coolant pump intermittently faulting, reducing heat transfer to and from the pack during charging Possible
• Scheduled Departure or preconditioning not configured, so the car never warms the pack before a cold-weather charge session Less Likely

Step-by-Step Diagnostic Procedure

1. Open the Tesla touchscreen service menu by holding down the brake pedal and pressing the two scroll wheel buttons simultaneously for about 10 seconds, then navigate to Energy > Battery to check current pack temperature before diagnosing anything else.

2. Connect a Scan My Tesla app using an OBDLink MX+ or Veepeak adapter plugged into the OBD port. Pull live BMS data and look at battery inlet temperature, outlet temperature, and the active warning list. Confirm BMS_w044 is logged and note the pack temperature at the time of fault.

3. Check the charge rate drop pattern. If charging starts slow and speeds up on its own after 20 to 40 minutes, the pack is simply warming up during the session and no component has failed. This is expected BMS thermal protection behavior.

4. Inspect the charge rate when plugging in at different battery temperatures. Plug in immediately after a 20-plus-mile highway drive in summer and note whether the rate is also limited. If so, the BMS is protecting an overheated pack, not a cold one.

5. Check the coolant reservoir under the hood. It is a translucent tank near the frunk. Verify fluid is between MIN and MAX. A low coolant level reduces the thermal system's ability to regulate pack temperature and can make BMS_w044 appear more frequently or persist longer.

6. Set up Scheduled Departure in the touchscreen under Charging. Schedule your typical departure time and enable Precondition. The car will run the battery heater and thermal loop before you unplug so the pack arrives at optimal temperature without consuming the full charge current to do it.

7. If the code appears persistently even when the pack is at a normal temperature, 60 to 80 degrees F, or if charge rate never recovers during a session, that points to a failing coolant pump, stuck thermal valve, or degraded cell group. At that point you need Tesla Toolbox 3 or a shop with CAN-level access to read thermal actuator feedback, which is beyond what Scan My Tesla can diagnose.

Frequently Asked Questions