Skip to main content
This tutorial shows how to process automotive or industrial time-series data (OBD-II / CAN) data in your project. We’ll keep things general by working from CSV logs and then replaying them into an exported .eim model on a Linux SBC (e.g., Raspberry Pi).

OBD formatted data

We’ll classify short windows as healthy vs air-leak + NOx fault. If you don’t have live hardware, you can still follow along entirely with CSV files.

Impulse

We’ll validate a known drivability issue: an intake air leak (lean condition) that can elevate NOx, often associated with P0171/P0174 DTCs. If you don’t have a vehicle or adapter handy, use the public project dataset: public project created for this tutorial.

​
Prerequisites

Before you begin, ensure you have the following:
  • An Edge Impulse account
  • A compatible OBD-II adapter (e.g., ELM327)
  • CSV of OBD-II data for healthy and unhealthy vehicle states
Take the sample CSV to get started or collect a sample from your OBD-II interface using your pi and the telemetry-obd project.

​
1. Problem overview

Goal: Detect an intake air leak from OBD-II signals by finding windows where NOx is disproportionately high relative to load (throttle / airflow / RPM).

​
Signals we will use

We’ll use a minimal, interpretable set (more can be added later):
  • MAF [g/s] : proxy for air mass entering the engine (load).
  • NOx [ppm] : emission outcome; rises with lean burn / mis-mix.
  • Throttle position [%] : driver demand / load request.
  • (Optional) RPM, MAP [kPa], Lambda, STFT/LTFT for context.
Healthy hypothesis: For a given load (MAF / throttle / RPM), NOx stays within a predictable range.
Leak hypothesis: With unmetered air, mixture trends lean > NOx is higher than expected for the same load.

​
2 Capture Options

**ELM327**

**ELM327** USB or Bluetooth logger

ELM327(USB/Bluetooth): simplest path to Mode 01 PIDs (RPM, throttle, MAF, etc.). CAN HAT (direct bus): robust for field installs/industrial; wire OBD-II PIN 6 (CAN-H), PIN 14 (CAN-L), PIN 4 (GND).
OBD pinout

**OBD-II** connector pinout

Pi HAT wiring

Pi Hat wiring

Safety note: Induce a small, reversible leak (loosen an intake boot or remove a tiny vacuum cap). unplug the airflow sensor (MAF/MAP) : this can trigger limp mode and confound data.

​
3 Data capture (reproducible method)

Capture
  • Sampling: 2 Hz (every 500 ms).
  • Drive cycle: idle > gentle accelerations > light cruise > decel.
  • Classes:
    • healthy: intact intake, warmed-up closed loop.
    • airleak_nox: the same drive cycle with a small, controlled leak.
  • Windows: 2000 ms window, 1000 ms step (overlapping).
  • Duration target: ~10 min per class (balanced).

​
4

Healthy window example

Healthy window (reference)

Leak window example : NOx too high relative to throttle/MAF (typical of a vacuum leak)

Air-leak window (high NOx vs load)

​
5 Simple, interpretable features (used by the classifier)

Over each 2 s window, compute:
  • nox_per_maf = NOx / max(MAF, 0.1)
  • nox_per_throttle = NOx / max(throttle, 1)
  • maf_per_rpm = MAF / max(RPM, 500)
  • Short-window mean and **slope ** for NOx and MAF
Decision intuition: Windows with high nox_per_maf and/or positive NOx slope at modest load are more likely air-leak. With the signals defined, wiring settled, and an explicit labeling protocol, we can now build the model.

​
2. Prepare the CSV

The CSV Wizard expects:
  • A time column named time (ms.) (milliseconds since the first sample)
  • One label column (here fault_label)
  • One numeric column per OBD signal
Take the sample CSV to get started or collect a sample from your OBD-II interface using your pi and the telemetry-obd project.
The CSVs for the sample project have the following headings: 
time (ms.),fault_label,RPM [RPM],PEDAL INPUT [%],MAF [g/s],NOx [ppm]

​
3. Import with the CSV Wizard

1.Open your project Data acquisition CSV Wizard
2. Upload n53_healthy_ei.csv and n53_faulty_ei.csv (or your own files)
3. Set Label column = fault_label and Time column = time (ms.)
4. Confirm sampling rate ≈ 2 Hz (every 500 ms)
5. Finish import : the wizard converts each file into time-aligned samples

​
4. Windowing (time-series slicing)

Use windows long enough for trims/lambda to show trends:
  • Window size: 3000 ms
  • Window increase: 1500 ms
This creates overlapping 3-second windows sliding every 1.5 s.

​
5. Create the impulse

  1. Go to Create impulse
  2. Input: your time-series window
  3. Processing block: Flatten (start simple)
    • (Optional) add Spectral features for fast-changing channels (e.g., mass_air_flow_gps, nox_sensor_ppm)
    • (Optional) enable Normalization if feature scales differ by ≥10×
  4. Learning block: Classification (Keras)
Flatten settings: defaults are fine.
Start with Flatten only. If accuracy plateaus, add Spectral features as a second block.

​
6. Generate features

Open Generate features and run on all samples.
Use Feature explorer to verify clusters separate (healthy vs. fault).

​
7. Train the classifier

In Classification (Keras):

Classification

Network (starter):
  • Dense 128 (ReLU) Dropout 0.20
  • Dense 64 (ReLU)
  • Dense N_classes (Softmax)
Training:
  • Split: 70/30 train/validation
  • Epochs: 50–100
  • Batch size: 32
  • Enable Class weighting if classes are imbalanced
Click Start training and review metrics.
Target: ≥ 95% precision/recall per class on the validation set.
  • Confusion matrix: identify misclassifications (e.g., healthy fault)
  • Feature explorer: confirm separation (trims/lambda/MAF/MAP)
  • If one sensor dominates (e.g., only NOx), add more context:
    • STFT/LTFT (fuel trims)
    • Lambda (bank1/2)
    • Ratios (e.g., maf_per_rpm, map_per_throttle)

​
9. Deploy

Open Deploy and choose your target:
  • Linux/Aarch64 (Raspberry Pi4)

​
Scripts

We have created a short script that will play back a recording of the CSV file and simulate real-time classification of the OBD-II signals. This allows us to test the model’s performance in a controlled environment before deploying it to a live vehicle, scripts and instructions are available from the public repository. obd automotive data Run the collection script to log data from your ELM327: 
python3 collect_obd_data.py \
  --model ./obd_fault.eim \
  --csv ./airleak_MAF_NOx.csv \
  --axes "RPM [RPM],PEDAL INPUT [%],MAF [g/s],NOx [ppm]" \
  --hz 2 --window-ms 1000 --step-ms 1000 --label-col fault_label
Play back the CSV file: 
python3 play_csv_to_eim.py \
  --model ./obd_fault.eim \
  --csv ./airleak_MAF_NOx.csv \
  --axes "RPM [RPM],PEDAL INPUT [%],MAF [g/s],NOx [ppm]" \
  --hz 2 --window-ms 1000 --step-ms 1000 --label-col fault_label
For live capture on Pi, a wired CAN HAT is typically more reliable than Bluetooth ELM clones. USB ELM327 also works well.

​
Conclusion

In this tutorial, we explored how to collect OBD-II data from vehicles using both Bluetooth adapters and direct CAN bus connections. This workflow generalizes to other vehicle faults (misfire, EGR, sensor bias) and industrial CAN signals.
⌘I