The On-Board Diagnostics II (OBDII) system in modern vehicles is a powerful tool, primarily designed for emissions monitoring and providing standardized diagnostic data. Many automotive enthusiasts and professionals wonder about expanding its capabilities: Can I Add Sensors To My Obdii system beyond its factory configuration? This question taps into the desire for more detailed vehicle data, custom monitoring, and enhanced diagnostics.
While the OBDII port itself is standardized, directly “adding sensors” to the OBDII system in a plug-and-play manner is not typically feasible in the way one might imagine adding USB devices to a computer. The OBDII protocol and the vehicle’s Engine Control Unit (ECU) are designed to read data from a specific set of sensors that are integral to the vehicle’s operation and emissions control. These sensors are hardwired into the vehicle’s electrical system and their data is processed by the ECU before being made available through the OBDII port.
However, the desire to monitor additional parameters or use custom sensors isn’t out of reach. The key is to understand that you’re not directly modifying the OBDII system itself, but rather interfacing with the vehicle’s data network, often the Controller Area Network (CAN bus), to introduce and interpret data from aftermarket sensors.
Exploring External Sensor Integration
For those looking to go beyond the standard OBDII data, the most common approach involves using external microcontrollers and sensor interfaces. Devices like ESP32 or ESP8266, as mentioned in some DIY projects, can be connected to the vehicle’s CAN bus. These microcontrollers can then:
- Read Existing OBDII Data: Tap into the CAN bus to read standard OBDII PIDs (Parameter IDs), accessing the same data available to diagnostic scanners.
- Incorporate Aftermarket Sensors: Connect to external sensors (like ethanol content sensors, oil temperature sensors, pressure sensors, etc.) and read their values.
- Translate and Transmit Data: Process the data from both OBDII and external sensors, and then transmit it wirelessly (e.g., via ESP-NOW or WiFi) to a custom display or logging system.
Understanding Torque PIDs and CAN Frames
A common point of confusion arises when trying to translate “Torque PIDs” into raw CAN frames. Torque PID is a term often used in conjunction with apps like Torque Pro, which uses predefined formulas to interpret OBDII data. These PIDs are essentially requests for specific data points using the OBDII protocol.
However, when working directly with the CAN bus, you’re dealing with raw CAN frames. Each frame has an identifier (CAN ID) and a data payload. To read a specific sensor value, you need to know:
- The CAN ID: The identifier of the CAN message that contains the desired sensor data. This is vehicle-specific and often requires reverse engineering or access to vehicle documentation.
- Data Position and Interpretation: Within the CAN frame’s data payload, the sensor value will be encoded in a specific format (e.g., bytes, bit positions). You need to know how to extract and decode this data, often using equations or lookup tables.
For example, the provided “Tire 1 Pressure” PID:
**pid: 222A05 name: Tire 1 Pressure sName: T1Press Min: 0 Max: 50 Scale: x1 Unit: psi Equation: ((A * 1373) / 1000) * 0.145037738 Header: 720**Indicates that to get Tire 1 Pressure:
- Header: 720 likely refers to the CAN ID in hexadecimal (0x720).
- pid: 222A05 is the Torque PID, which might be used by diagnostic tools to request this data.
- Equation: ((A * 1373) / 1000) * 0.145037738 shows how to convert the raw data byte ‘A’ (presumably from the CAN frame payload) into PSI.
To get the CAN frame, you’d typically need to listen to CAN traffic, identify messages with CAN ID 0x720, and then extract the relevant byte (or bytes) from the data payload. The exact byte position and the scaling equation are crucial for correct interpretation.
Practical Applications and Considerations
Adding external sensors and integrating them with vehicle data opens up numerous possibilities:
- Custom Gauges: Displaying parameters not available on the factory dashboard, such as oil temperature, boost pressure (for turbocharged vehicles), or ethanol content.
- Performance Monitoring: Creating custom logging systems to track performance metrics and identify areas for improvement.
- Advanced Diagnostics: Monitoring parameters beyond standard OBDII for more in-depth troubleshooting.
However, there are important considerations:
- Vehicle Network Complexity: Modern vehicle CAN bus systems can be complex, with multiple CAN networks. Identifying the correct CAN bus and CAN IDs for desired data requires expertise.
- Potential for Interference: Improper connections or code can potentially disrupt vehicle communication. Caution and thorough testing are essential.
- Data Interpretation: Decoding CAN data requires knowledge of vehicle-specific protocols and data encoding methods.
- Warranty and Liability: Modifications to vehicle electronics may affect warranties and could have liability implications.
Conclusion
While you cannot directly “add sensors” to the OBDII system in a simplistic way, you can certainly integrate aftermarket sensors and expand vehicle data monitoring by interfacing with the CAN bus. This involves using external microcontrollers, understanding CAN communication, and potentially reverse-engineering vehicle-specific data protocols. For experienced automotive technicians and DIY enthusiasts with electronics skills, this opens up a realm of possibilities for customized vehicle data acquisition and display. However, it’s crucial to proceed with caution, proper research, and a thorough understanding of the vehicle’s electrical and communication systems.
