OBD-II

OBD2 Scanner User Guide

Overview

The OBD2 Scanner module provides comprehensive vehicle diagnostics and data acquisition through the On-Board Diagnostics II (OBD2) protocol. This guide covers configuration, operation, and troubleshooting.

Table of Contents

• Quick Start
• Configuration
• Status Monitoring
• Supported Services
• Advanced Features
• Troubleshooting
• Examples

Quick Start

Prerequisites

• Vehicle with OBD2 port (1996+ vehicles in most regions)
• CAN bus connection to vehicle OBD2 port
• OBD2 adapter cable or direct CAN connection

Basic Setup

1. Enable OBD2 on CAN Bus

   • Navigate to CAN Bus settings
   • Enable OBD2 scanner on desired CAN bus (typically can0)
   • Set request interval (recommended: 100-200ms for standard polling)

2. Configure Service 0x01 (Current Data)

   • Enable Service ID: 1 (0x01)
   • Enable PID Discovery for automatic detection
   • Add PIDs you want to monitor (see Standard PIDs)

3. Test Connection

   • Check OBD2 Service Status channel
   • Should show “Connected” when receiving data
   • Check OBD2 Poll Rate to verify polling frequency

Configuration

CAN Bus Settings

CAN Bus: can0
├── OBD2 Enabled: Yes
├── Request Interval: 100ms (adjustable 50-1000ms)
└── Services:
    └── Service 0x01 (Show Current Data)

Service Configuration

Each OBD2 service (0x01, 0x09, 0x22, etc.) can be independently configured:

PID Configuration

For each PID you want to monitor:

Status Monitoring

Status Channels

Monitor OBD2 system health through these channels:

Global Status

Per-Service Status (Service 1-8)

Status Values

Disabled          = 0  // Service not enabled
Connected         = 1  // Receiving valid data
No Response       = 2  // Not receiving responses (timeout after 5x poll interval)
PID Not Supported = 3  // ECU reports PID not supported
Response Error    = 4  // Other communication error

Supported Services

Service 0x01: Show Current Data

Real-time engine and vehicle parameters.

Configuration:

• PID Width: 1 byte
• Supports batch requests (up to 6 PIDs per request)
• Supports PID discovery (recommended)

Common Use: Engine RPM, coolant temp, throttle position, vehicle speed

Service 0x09: Vehicle Information

Static vehicle identification data.

Configuration:

• PID Width: 2 bytes
• Single PID per request (no batching)
• Discovery optional

Common Use: VIN, calibration IDs, ECU name

Service 0x22: Read Data By Identifier (UDS)

Manufacturer-specific extended data.

Configuration:

• PID Width: 2 bytes
• Single PID per request
• Discovery not typically supported

Common Use: Custom manufacturer parameters, advanced diagnostics

Advanced Features

Multi-PID Polling (Batch Requests)

Request multiple PIDs in a single CAN message for faster polling.

Benefits:

• Higher effective poll rate
• Reduced CAN bus traffic
• Lower latency

Limitations:

• Only Service 0x01 supports this (per SAE J1979)
• Maximum 6 PIDs per request
• Must use physical addressing (0x7E0) not broadcast (0x7DF)
• Some ECUs may not support this feature

Configuration:

Service 0x01:
├── Batch PID Requests: Yes
├── TX Address: 0x7E0 (physical addressing required)
└── PIDs: [0x0C, 0x0D, 0x05, 0x0F, 0x10, 0x11]

Expected Poll Rate:

• 6 PIDs with 100ms interval = ~10 Hz per PID
• Without batching = ~1.6 Hz per PID

PID Discovery

Automatically detect which PIDs your vehicle supports.

How It Works:

1. System queries PID 0x00 (supported PIDs 0x01-0x20)
2. System queries PID 0x20 (supported PIDs 0x21-0x40)
3. Continues for PID ranges: 0x40, 0x60, 0x80, 0xA0, 0xC0
4. Only polls PIDs that are marked as supported
5. Falls back to polling all configured PIDs if discovery fails

Benefits:

• Faster polling (skips unsupported PIDs)
• Better compatibility
• Automatic adaptation to vehicle capabilities

Retry Logic:

• 3 retry attempts if discovery times out
• 2-second timeout per attempt
• Falls back to polling mode if all retries fail

Custom Decode Formulas

Convert raw PID data to engineering units using mathematical expressions.

Formula Variables:

• A = First data byte (0-255)
• B = Second data byte (0-255)
• C = Third data byte (0-255)
• D = Fourth data byte (0-255)
• E to H = Additional bytes if needed

Examples:

// Engine RPM (PID 0x0C, 2 bytes)
(A*256 + B) / 4

// Coolant Temperature (PID 0x05, 1 byte)
A - 40

// Throttle Position (PID 0x11, 1 byte)
A * 100 / 255

// Fuel Pressure (PID 0x0A, 1 byte, result in kPa)
A * 3

// Intake Air Temperature (PID 0x0F, 1 byte, result in °C)
A - 40

// MAF Sensor (PID 0x10, 2 bytes, result in g/s)
(A*256 + B) / 100

// O2 Sensor Voltage (PID 0x14, 2 bytes)
A / 200  // Voltage (V)
// B = Short term fuel trim (%)

// Vehicle Speed (PID 0x0D, 1 byte, result in km/h)
A

// Runtime since engine start (PID 0x1F, 2 bytes, result in seconds)
A*256 + B

// Fuel Tank Level (PID 0x2F, 1 byte, result in %)
A * 100 / 255

Standard PIDs

Service 0x01 Common PIDs

Service 0x09 Common PIDs

Troubleshooting

Connection Issues

“No Response” Status

Symptoms: Status shows “No Response” or never connects

Causes:

1. Vehicle not in RUN or ENGINE ON mode
2. Incorrect CAN bus connection
3. Wrong CAN bitrate (should be 500 kbps for OBD2)
4. CAN termination issues

Solutions:

1. Verify vehicle ignition is ON
2. Check physical CAN bus wiring (CAN-H and CAN-L)
3. Confirm CAN bitrate: 500 kbps or 1 Mbps
4. Check CAN termination (120Ω between CAN-H and CAN-L)
5. Try both physical (0x7E0) and broadcast (0x7DF) request addresses

“PID Not Supported” Status

Symptoms: Status shows “PID Not Supported” with error code 0x11 or 0x12

Causes:

1. Vehicle doesn’t support the requested PID
2. Service not available on this vehicle/ECU
3. PID configuration error

Solutions:

1. Enable PID Discovery to auto-detect supported PIDs
2. Check vehicle OBD2 compliance level
3. Try Service 0x01 PIDs first (universal)
4. Verify PID byte count matches specification
5. Some vehicles only support basic PIDs (0x00-0x20)

Low Poll Rate

Symptoms: OBD2 Poll Rate < 1 Hz, data updates slowly

Causes:

1. Too many PIDs configured
2. Request interval too high
3. Multi-PID batching disabled

Solutions:

1. Reduce number of active PIDs
2. Decrease request interval (minimum 50ms recommended)
3. Enable Batch PID Requests (Service 0x01 only)
4. Use physical addressing (0x7E0) for faster responses
5. Check OBD2 Response Rate - should be >80%

Low Response Rate

Symptoms: OBD2 Response Rate < 80%, intermittent data

Causes:

1. CAN bus errors or noise
2. ECU busy with other operations
3. Too short request interval
4. Poor connection quality

Solutions:

1. Increase request interval (try 200ms)
2. Check CAN bus wiring quality
3. Verify CAN termination
4. Monitor CAN bus load (should be <70%)
5. Check for CAN errors in bus statistics

Data Issues

Incorrect Values

Symptoms: Channel values don’t match expected ranges

Causes:

1. Wrong decode formula
2. Incorrect byte count
3. Byte order mismatch

Solutions:

1. Verify formula against OBD2 specification
2. Check byte count matches PID definition
3. Test with known PIDs first (RPM, Speed)
4. Compare with other scan tools
5. Check formula syntax (use A, B, C, D for bytes)

Flickering/Unstable Values

Symptoms: Values jump erratically between readings

Causes:

1. Poll rate too high causing data race
2. Formula error causing invalid calculations
3. CAN bus errors corrupting data

Solutions:

1. Increase poll interval
2. Verify formula produces valid output
3. Check CAN bus quality
4. Monitor OBD2 Response Rate for drops

Discovery Issues

Discovery Never Completes

Symptoms: Service stuck in “Disabled” state, never reaches “Connected”

Causes:

1. Discovery timeout (vehicle doesn’t respond to PID 0x00)
2. Vehicle doesn’t support discovery
3. Wrong service configuration

Solutions:

1. Wait for 3 retry attempts (6+ seconds)
2. Disable PID Discovery to skip auto-detection
3. Manually configure known PIDs
4. Check logs for timeout messages
5. Some vehicles require specific timing

Discovery Detects No PIDs

Symptoms: Discovery completes but no PIDs are polled

Causes:

1. Vehicle returned empty bitmap
2. No configured PIDs match supported PIDs
3. Discovery misinterpretation

Solutions:

1. Manually configure common PIDs (0x0C, 0x0D, 0x05)
2. Disable discovery and poll all configured PIDs
3. Try Service 0x01 PIDs 0x00-0x20 first
4. Check Supported PIDs bitmap channels for values

Performance Optimization

Maximizing Poll Rate

Goal: Achieve 10+ Hz poll rate for critical parameters

Strategy:

1. Enable Batch PID Requests (Service 0x01)
2. Use physical addressing (0x7E0)
3. Request only essential PIDs (6 maximum per batch)
4. Set request interval to 100ms
5. Ensure vehicle supports multi-PID requests

Expected Results:

• 6 PIDs @ 100ms interval = ~10 Hz per PID
• Total CAN messages = ~10/second
• Response rate should be >90%

Minimizing CAN Bus Load

Goal: Reduce CAN bandwidth usage

Strategy:

1. Increase request interval (200-500ms)
2. Disable unused PIDs
3. Use batch requests to consolidate messages
4. Prioritize essential parameters

CAN Load Calculation:

Single PID request = 1 frame (~10 bytes @ 500kbps = ~200µs)
Response = 1-8 frames depending on data size
Total per poll = 2-9 frames

Example: 10 PIDs @ 100ms interval
= 10 requests/second × 2 frames avg = 20 frames/sec
= ~4 kbps out of 500 kbps = <1% bus load

Balancing Multiple Services

Scenario: Monitor Service 0x01 (current data) and Service 0x09 (VIN)

Strategy:

Service 0x01:
├── Request Interval: 100ms
├── PIDs: High-frequency data (RPM, Speed, Throttle)
└── Batch Requests: Yes

Service 0x09:
├── Request Interval: 1000ms (slower)
├── PIDs: Static data (VIN, Calibration ID)
└── Batch Requests: No

Examples

Example 1: Basic Engine Monitoring

Monitor essential engine parameters.

Configuration:

Service 0x01:
  - Enabled: Yes
  - PID Discovery: Yes
  - Batch PID Requests: Yes
  - Request Interval: 100ms
  - TX Address: 0x7E0

PIDs:
  PID 0x0C (Engine RPM):
    - Channel ID: 60100
    - Byte Count: 2
    - Formula: (A*256+B)/4

  PID 0x0D (Vehicle Speed):
    - Channel ID: 60101
    - Byte Count: 1
    - Formula: A

  PID 0x05 (Coolant Temp):
    - Channel ID: 60102
    - Byte Count: 1
    - Formula: A-40

  PID 0x11 (Throttle Position):
    - Channel ID: 60103
    - Byte Count: 1
    - Formula: A*100/255

Expected Results:

• Poll Rate: ~10 Hz
• Response Rate: >90%
• 4 parameters updated 10 times per second

Example 2: Performance Logging

High-speed data acquisition for track use.

Configuration:

Service 0x01:
  - Request Interval: 50ms (20 Hz)
  - Batch PID Requests: Yes
  - TX Address: 0x7E0

PIDs (6 max per batch):
  - 0x0C: Engine RPM
  - 0x0D: Vehicle Speed
  - 0x10: MAF Air Flow
  - 0x11: Throttle Position
  - 0x0F: Intake Air Temp
  - 0x0B: Intake Manifold Pressure

Expected Results:

• Poll Rate: 20 Hz
• 6 channels @ 20 Hz = 120 samples/second total
• CAN load: ~2%

Example 3: Diagnostic Scan

Complete vehicle parameter survey.

Configuration:

Service 0x01:
  - PID Discovery: Yes
  - Request Interval: 200ms
  - Batch PID Requests: No (for maximum compatibility)
  - TX Address: 0x7DF (broadcast)

PIDs: All supported PIDs (auto-detected via discovery)

Service 0x09:
  - Request Interval: 5000ms
  - PIDs: 0x02 (VIN), 0x04 (Calibration ID)

Expected Results:

• Automatic detection of 20-40 supported PIDs
• Poll rate: 2-5 Hz depending on PID count
• VIN and calibration data refreshed every 5 seconds

Example 4: Manufacturer-Specific (UDS)

Access extended manufacturer parameters.

Configuration:

Service 0x22 (UDS):
  - PID Width: 2
  - PID Discovery: No
  - Batch PID Requests: No
  - TX Address: 0x7E0

PIDs (manufacturer-specific examples):
  PID 0xF190:
    - Description: "Boost Pressure"
    - Channel ID: 60200
    - Byte Count: 2
    - Formula: (A*256+B)/100

  PID 0xF191:
    - Description: "Fuel Rail Pressure"
    - Channel ID: 60201
    - Byte Count: 2
    - Formula: (A*256+B)*10

Note: Manufacturer PIDs vary by make/model. Consult manufacturer documentation.

Technical Reference

CAN Message Format

OBD2 Request (Single PID):

ID: 0x7DF (broadcast) or 0x7E0 (physical)
Data: [0x02, 0x01, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00]
       │     │     │
       │     │     └─ PID (0x0C = RPM)
       │     └─────── Service (0x01)
       └───────────── Length (2 bytes)

OBD2 Request (Multi-PID):

ID: 0x7E0 (physical addressing required)
Data: [0x04, 0x01, 0x0C, 0x0D, 0x05, 0x00, 0x00, 0x00]
       │     │     │     │     │
       │     │     │     │     └─ PID 3 (0x05 = Coolant Temp)
       │     │     │     └─────── PID 2 (0x0D = Speed)
       │     │     └───────────── PID 1 (0x0C = RPM)
       │     └─────────────────── Service (0x01)
       └───────────────────────── Length (4 bytes)

OBD2 Response:

ID: 0x7E8 (or 0x7E9-0x7EF for multiple ECUs)
Data: [0x04, 0x41, 0x0C, 0x1A, 0xF8, 0x00, 0x00, 0x00]
       │     │     │     │     │
       │     │     │     └─────┴─ Data bytes (0x1AF8 = 6904 → RPM = 1726)
       │     │     └───────────── PID echo (0x0C)
       │     └─────────────────── Response mode (0x41 = 0x01 + 0x40)
       └───────────────────────── Length (4 bytes)

ISO-TP Multi-Frame

For responses >7 bytes, ISO-TP (ISO 15765-2) is used:

First Frame:

[0x10, 0x14, 0x49, 0x02, 0x01, ...]
  │     │     └─────────────────── Start of data
  │     └───────────────────────── Total length (0x14 = 20 bytes)
  └─────────────────────────────── Frame type (0x1 = First Frame)

Consecutive Frames:

[0x21, data, data, data, ...]
  │
  └─ Sequence number (0x21 = frame 1, 0x22 = frame 2, etc.)

Negative Response Codes

Safety and Compliance

Legal Considerations

• Regional Compliance: OBD2 is mandated for vehicles sold in:

  • USA: 1996+
  • EU: 2001+ (gasoline), 2004+ (diesel)
  • Australia: 2006+
  • Other regions vary

• Emissions Testing: Tampering with OBD2 data may violate emissions regulations

• Warranty: Check vehicle warranty terms regarding aftermarket scanning

Best Practices

1. Non-Intrusive: Read-only monitoring doesn’t affect vehicle operation
2. Passive Scanning: This module only reads data, never writes
3. Standard Compliant: Follows SAE J1979 and ISO 15765-2 specifications
4. ECU Protection: Respects timeouts and retry limits to avoid ECU overload

Limitations

• Manufacturer-Specific Data: Some parameters require proprietary protocols
• Real-Time Constraints: Not suitable for safety-critical applications
• CAN Bus Priority: OBD2 messages are low priority; critical vehicle systems take precedence
• ECU Availability: Some ECUs may be busy and unable to respond immediately

Glossary

Additional Resources

Standards Documents

• SAE J1979: OBD2 Diagnostic Test Modes
• ISO 15765-2: Diagnostic communication over CAN
• ISO 14229-1: Unified Diagnostic Services (UDS)
• SAE J2012: Diagnostic Trouble Code Definitions

Tools and Validation

• Use OBD2 scan tool to verify vehicle responses
• Compare results with known-good scanner
• Monitor CAN bus with analyzer to debug issues
• Test with multiple vehicles for compatibility

Support

For additional help:

1. Check system logs for detailed error messages
2. Review CAN bus statistics for communication issues
3. Verify configuration against examples in this guide
4. Test with minimal configuration first (basic PIDs)

Revision History