ESP32 OBD2 CAN Logger

A DIY OBD2 data logger built with an ESP32. Reads live engine data over CAN bus, logs to CSV (SD card or internal flash), shows live values on a small OLED display, and serves a real-time web dashboard over WiFi.

Note: Only tested on a 2020 Tata Nexon 1.2L Turbo Petrol (6-speed manual). Should work on any car with standard OBD2 over CAN (ISO 15765-4, 500 kbps).

Using AI to review your driving data

Download the CSV from the WiFi dashboard and upload it to an AI model like Claude or Gemini Pro. You can ask questions like:

• "How is the turbo performance?"
• "Review if all sensors are working correctly and flag any issues"
• "Is the fuel trim normal or is the engine running rich/lean?"
• "Any signs of engine problems based on this data?"

The AI can analyze thousands of rows of sensor data in seconds and give you a plain-English health report of your car.

Here's an example report generated from a real driving session:

What it does

• Reads 30+ OBD2 PIDs: RPM, speed, coolant temp, oil temp, MAP, IAT, engine load, timing advance, throttle, accelerator pedal, fuel trims, O2 sensors, catalyst temp, fuel rate, voltage, and more
• Logs to CSV at ~4 Hz with automatic session numbering — SD card preferred, falls back to ESP32 internal flash (LittleFS) if no SD card is present
• OLED display (optional) — rotates between live data, running averages, and session stats (max boost, trip distance, fuel economy)
• WiFi dashboard — connect your phone to see live gauges, download CSV files, and check PID status
• Smart polling — fast-changing PIDs polled at ~4 Hz, slow-changing PIDs at ~1 Hz
• Auto-disables unsupported PIDs — if a PID times out 10 times in a row, it stops polling it
• Estimates current gear from RPM/speed ratio (calibrated for Nexon 6MT gearbox)

Parts list

Part	Notes
ESP32 Dev Board	Any ESP32-WROOM-32 dev board works
TJA1050 CAN Module	5V module — needs a voltage divider on RX (see wiring). A 3.3V CAN module (e.g. SN65HVD230) is easier if you can find one
Micro SD Card Module (optional)	HW-125 with onboard level shifter. Power from 5V. Without it, logs to ESP32 internal flash (~1.5 MB)
0.96" SSD1306 OLED Display (optional)	128x64, I2C. The logger works without it
OBD2 Extension Cable	16-pin male to female — splice into the male end for CAN High/Low
SD Card (optional)	I use a SanDisk Ultra 64GB. Any size works — CSV files are small
Jumper wires, solder, etc.	--

I mostly order from robocraze.com or robu.in — check both for availability and pricing.

Wiring

Full wiring details below.

ESP32 to TJA1050 CAN Module

ESP32 GPIO5  ──────────────────  TJA1050 TXD
ESP32 GPIO4  ──┬── 1kΩ ────────  TJA1050 RXD     (voltage divider: 5V → 3.4V)
               └── 2.2kΩ ─────  GND
ESP32 5V     ──────────────────  TJA1050 VCC
ESP32 GND    ──────────────────  TJA1050 GND

If using a 3.3V CAN transceiver (e.g. SN65HVD230), skip the voltage divider and connect RX directly.

TJA1050 to OBD2 Connector

TJA1050 CANH  ──  OBD2 Pin 6  (CAN High)
TJA1050 CANL  ──  OBD2 Pin 14 (CAN Low)
TJA1050 GND     ──  OBD2 Pin 4 or 5  (Chassis/Signal Ground)

ESP32 to SD Card Module (HW-125) — optional

ESP32 GND    ──  GND
ESP32 5V     ──  VCC
ESP32 GPIO19 ──  MISO
ESP32 GPIO23 ──  MOSI
ESP32 GPIO18 ──  SCK
ESP32 GPIO15 ──  CS

If no SD card module is connected, the logger automatically falls back to the ESP32's internal flash (LittleFS, ~1.5 MB). This gives you roughly 30 minutes of logging. Download the CSV over WiFi before it fills up.

ESP32 to OLED Display (optional)

ESP32 GND    ──  GND
ESP32 3.3V   ──  VCC
ESP32 GPIO21 ──  SDA
ESP32 GPIO22 ──  SCL

Flashing

Prerequisites

1. Install the Arduino IDE (v2.x recommended)

2. Add ESP32 board support:

   • Go to Tools → Board → Boards Manager, search "esp32", install esp32 by Espressif Systems

3. Install required libraries via Sketch → Include Library → Manage Libraries:

   • Adafruit SSD1306
   • Adafruit GFX Library

   (SD, SPI, Wire, WiFi, and WebServer are included with the ESP32 board package.)

Upload

1. Connect the ESP32 via USB
2. Open main/main.ino in Arduino IDE
3. Select your board: Tools → Board → ESP32 Dev Module
4. Select the correct port: Tools → Port
5. Click Upload

Usage

1. Power up

Plug the ESP32 into the car's USB port (or a USB power bank for bench testing). The OBD2 extension cable connects to the car's OBD2 port under the dashboard.

On startup, the OLED (if connected) shows:

Nexon CAN Logger

SD  Session #1            (or "LittleFS  Session #1" if no SD card)
Total: 59000 MB
Used:  12 MB
Free:  58988 MB

The serial monitor (115200 baud) shows the same info plus CAN bus init status.

2. Connect to the WiFi dashboard

1. On your phone, connect to WiFi network: obd2logger (password: logger@ka01)
2. Open a browser and go to http://192.168.4.1

You'll see a live dashboard with all the gauges updating every second:

• Dashboard (/) — live gauges for all PIDs, storage bar, download/session links
• All Sessions (/sessions) — list of all logged sessions with download and delete options
• Download Current (/download) — download the active session CSV
• Debug Log (/log) — ring buffer of recent debug messages
• PID Status (/timeouts) — see which PIDs are responding and which got auto-disabled

3. Data logging

Logging starts automatically on boot. Each power cycle creates a new session file (s001.csv, s002.csv, ...). With an SD card, files are stored in /data/ on the card. Without one, they go to the ESP32's internal flash (LittleFS).

CSV columns:

Timestamp_ms, RPM, Speed_kmh, Coolant_C, OilTemp_C, MAP_kPa, IAT_C,
Load_pct, TimingAdv_deg, Throttle_pct, AccelPedal_pct, CmdThrottle_pct,
DemandTorque_pct, ActualTorque_pct, STFT_pct, LTFT_pct, Baro_kPa,
O2S2_V, O2S2_STFT_pct, CmdEquivRatio, CatalystTemp_C, O2_SecLTFT_pct,
Gear, FuelLevel_pct, FuelRate_Lph, ModuleVoltage_V, AmbientTemp_C,
RefTorque_Nm, O2S1_Lambda, O2S1_Current_mA, AbsLoad_pct, EvapPurge_pct

4. Serial monitor output

At 115200 baud, you'll see a continuous stream like:

RPM:850 Spd:0 Clt:82 Oil:78 MAP:33 IAT:42 Load:18% Tmg:6.5 Thr:14% ...

Plus periodic status:

[12345] TX:482 RX:391 RX_timeout:91
[12345] TWAI state:1 txErr:0 rxErr:0 txQ:0 rxQ:0

Notes

• SD card is optional. If no SD card is found, the logger falls back to ESP32 internal flash (LittleFS, ~1.5 MB). That's roughly 30 minutes of logging at 4 Hz — download the CSV over WiFi before it fills up. If neither SD nor LittleFS can mount, the ESP32 won't start (nothing to log to).
• OLED is optional. If not connected, everything else works normally.
• Not all PIDs will work on every car. The logger auto-disables PIDs that your car's ECU doesn't support. Check the PID Status page (/timeouts) to see which ones your car responds to.
• Gear estimation is calibrated for the Nexon 1.2T 6-speed manual gearbox. If you're using a different car, you'll need to adjust the GEAR_RATIO_MIN[] and GEAR_RATIO_MAX[] arrays in the code.
• WiFi range is limited to a few meters — it's meant for use inside the car.

License

This project is licensed under CC BY-NC 4.0 — free to use, share, and modify for non-commercial purposes with attribution. No warranty.