I recently had a recurring error CC_a027 from my Tesla Wall Connector V3 that would give three red error LED blinks, send a notification of a charge error to my phone and the in-car display, and reduce the charge rate from whatever to was set to down to 6A. My Wall Connector was about six months past its four-year warranty, so I was on my own to fix this or buy a replacement. According to Tesla’s documentation this could be due to a number of faults.

I was able to fix my issue, which was a loose connector for the charge cable button/temp sensor. This was reported from /api/1/vitals as a handle_temp_c value of 255.0, which could either mean my charge handle, cable, and probably car are sitting at a toasty 255C, which seems unlikely as this is probably above the melting point of the glass-reinforced plastic type 2 plug, or more likely, there was something wrong with the sensor or associated hardware.

/api/1/vitals output:

{"contactor_closed":false,"vehicle_connected":true,"session_s":40519,"grid_v":234.9,"grid_hz":49.926,"vehicle_current_a":0.6,"currentA_a":0.6,"currentB_a":0.4,"currentC_a":0.4,"currentN_a":0.5,"voltageA_v":0.0,"voltageB_v":0.0,"voltageC_v":3.0,"relay_k1_v":11.9,"relay_k2_v":0.0,"pcba_temp_c":18.0,"handle_temp_c":255.0,"mcu_temp_c":24.1,"uptime_s":41523,"input_thermopile_uv":-183,"prox_v":0.1,"pilot_high_v":8.7,"pilot_low_v":-11.6,"session_energy_wh":3742.700,"config_status":5,"evse_state":4,"current_alerts":[],"evse_not_ready_reasons":[1]}

These are the resources I found along the way:

• Tesla Fault Codes: https://www.tesla.com/ownersmanual/2017_2023_model3/en_au/GUID-9A3F0F72-71F4-433D-B68B-0A472A9359DF.html#CC_A027
• Tesla Wall Connector V3 LED errors: https://energylibrary.tesla.com/docs/Public/Charging/WallConnector/Gen3/Install/3PT2/MID/en-us/GUID-F392579E-7C00-492D-9DE9-C97AF1808831.html
• Direct access to the Wall Connector API, including sensor states: [local IP address on your network]/api/1/vitals. eg. 192.168.0.2/api/1/vitals
• A video guide for removing the Wall Connector V3 faceplate and internal access: https://www.youtube.com/watch?v=aErAOchPlag, from https://tessories.com.au/product/tesla-wall-connector-replacement-cable/