How it works in one minute
OBD dongle
It works for some owners but takes patience, and the manufacturer can break it at any time. Your feedback will move this guide forward.
(WiCAN)Home
Wi-FiMosquitto
(MQTT)Home
Assistant
| What it is | A dongle in the diagnostic (OBD) port that queries the car and sends values over MQTT through your Wi-Fi |
| Cost | About €76 once (WiCAN Pro) |
| Data | Battery level at least; depending on known parameters: voltage, current, battery temperature |
| Commands | None: read-only |
| Where it works | Only when the car is in range of your Wi-Fi |
| Depends on | None: everything stays at home; but parameters vary by model |
What you need
- Home Assistant installed and reachable from your computer.
- The Mosquitto broker (official app, Settings → Apps → Store (Add-ons on older versions)) and the MQTT integration. If you already use Zigbee2MQTT, you have them.
- A WiCAN Pro (part
MP-WICAN-PRO, made by MeatPi), about €76 from Mouser. - 2.4 GHz Wi-Fi reaching where the car is parked.
- A dedicated Home Assistant user for MQTT (for example
mqtt-byd).
1Install the integration
- Plug in and set up the WiCANPlug it into the OBD port, join the Wi-Fi network it creates, change its password, then connect it to your Wi-Fi and to MQTT. These steps are detailed in our Xpeng guide: they're the same for BYD. Set the protocol to AutoPID.
- Look for a profile for your modelAutomate tab → Vehicle Profiles: if your BYD is listed, load its profile and skip to step 4.
- Otherwise, add the battery level by handA Dolphin owner shared this parameter, taken from A Better Route Planner. Add it as a custom parameter, then check the value against the dashboard: For other models, start from the community BYD PID list.
ECU 7E7 Request 221FFC Formula (A + B*256) / 100 - Wake the car and compareIgnition on, compare the percentage in Home Assistant with the car's. If it's off by a factor of 100, fix the formula.
OBD parameters change from one model and year to another, and BYD can change them in an update. Share what works on your car: that's how this guide will become reliable.
2The data you get
| Data | What it's for |
|---|---|
| Battery level (SoC) | In %, the value to give Watt Budget |
| Battery voltage | If the parameter is known for your model |
| Battery current | Positive when charging, negative when driving, depending on the model |
| Battery temperatures | If the parameter is known |
| 12 V voltage | Read by the dongle itself |
| Last reading | To know whether the car is asleep |
Replace the long names with short ones, for example sensor.byd_battery (Settings → Devices & services → Entities → the entity → cog). Your cards, automations and Watt Budget settings will be much easier to read.
3Connect Watt Budget
The sensor to enter in Watt Budget, under Settings › Home Assistant: the battery level sensor (in %) the WiCAN publishes over MQTT.
Once connected, Watt Budget reads the level every minute: no more typing the starting percentage, and the charge is worked out from the real battery level.
The four steps (HTTPS access, token, sensors, check) are explained on the guides home page and in the Watt Budget guide.
4Precautions
- Set the WiCAN's sleep threshold just above the sleeping car's 12 V voltage, so it sleeps with the car.
- Leased car: check your contract before leaving a dongle plugged in. It comes out in two seconds.
- Don't shorten the update interval: each query can wake the car and drain its 12 V battery. The defaults are a good balance.
- Your credentials stay in your Home Assistant; neither Watt Budget nor I can see them.
Frequently asked questions
Is there really no cloud solution?
Paid services go through BYD partners (they read a few values a day). Others script the Android app on an old phone. The OBD dongle remains the most reliable and most local option.
The level stops updating when the car is parked. Is it broken?
No: a sleeping car stops answering, and the dongle sleeps too. Data comes back when it wakes.
Does Watt Budget get access to my car?
No. Watt Budget only reads the battery level sensor in your Home Assistant, from your browser, with the token you give it. It never sees your manufacturer login or the car's location.
My model isn't listed. Can it work?
Often yes: these integrations go through the manufacturer's app, shared across the range. The easiest is to try, then tell me how it went via the contact page.
Links and thanks
Thanks to BYD owners sharing their OBD parameters, to the MeatPi team for the WiCAN, and to the A Better Route Planner community.
Does your car reach Home Assistant another way? Share your method: the next guides will follow your feedback.
The other Home Assistant guides
What does a charge really cost you? Off-peak tariffs, solar, rapid chargers and XCombo codes: Watt Budget works it all out, free and without an account.
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