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Roddrz · 02-06-2026, 10:18 PM

CAN Bus Security Dongle Design Guide

Security Dongle Design Summary

Overview

A cost-effective DIY security solution ($35 in components) contained in a single OBD2 dongle that prevents vehicle theft by disabling CAN bus access to the OBD2 service port.

Design Philosophy

Keep your doors unlocked approach: Focuses on preventing key programming rather than preventing window break-ins
CAN Bus vulnerability mitigation: Disables source of vulnerability through service port
No stock wires or connectors are cut

How the Security Dongle Functions
Core Mechanism

The dongle operates through a "miniature DPDT wireless relay" that controls CAN bus access to the service port:

Default State: When unplugged or disarmed, the relay disconnects the CAN bus signal to the service OBD2 port
Armed State: User presses the FOB button to activate the relay, connecting the CAN bus to the service port
Set and Forget: Once armed, the relay remains latched until power is removed from the dongle or the dongle is unplugged

Installation Process

Connect the relay control wire to the CAN bus twisted pair that controls access to the service OBD2 port
Relay gets it's power by 12V and ground pins from dummy OBD2 port
Add 120 Ohm terminating resistors across GMLAN pairs to trick FOB programmer into detecting a data link
Solidly tape the Data Link Connector to BCM and tye wrap the connector under the dash
Install security plate using security screws over BCM wire connectors

Build & Installation Time

Harness and Relay Build: 8 hours
Security Plate Build: 5 hours
Installation: Wire and security plate installation takes approximately 1 hour
Total: Approximately 14 hours

Parts List ($35 total)

12V Wireless Remote Control Switch: $13.00
Harness: $12
Small OBD2 connector dongle case: $8.00

Benefits & Safety Advantages
Security Design Philosophy

CAN Bus Protection: Blocks unauthorized key programming through OBD2 service port
Dummy Port Concept: Uses a dummy OBD2 port to obscure the actual service port location
Physical Barriers: Solid aluminum cover (1/8" thick) over BCM wire connectors with security screws prevents vampire clamp access

Operational Advantages

No User Friction: Set and forget operation—arm once, no re-arming required until power interruption
Integrated Concepts: Combines two proven security methods:
"Keep Hope Alive's" Dummy Plug concept
Ravelco's anti-theft device principles
Compact Design: Smaller form factor dongle case (half previous size, not shown) that fits the wireless relay perfectly, enabling discreet installation

Theft Prevention Scenario
Even if a thief:

Pulls the dongle from the dummy port
Finds and accesses the live OBD2 service port
Cannot program a new key because CAN bus access is disabled until dongle is reinserted and armed with the FOB
However, if they manage to find the OEM OBDII port or vampire clamp onto the BCM wires then they are away to the races.

Test Results (1 Year)
Performance Validation

One Year of Flawless Testing: The concept has been tested and working without failure for a full year
Component Reliability: Test parts fit perfectly with a very small case for the wireless relay

Relay Durability Analysis

Rated Operations: 100,000 minimum operations at heavy load (30VDC, 1 Amp)
Actual Usage Estimate: Only 20-40 relay toggles over vehicle service life
Margin of Safety: 2,500x safety margin (100,000 rated vs. 40 estimated operations)
Holding Current: Only 8 mA when latched (12V / 1440Ω coil resistance)

Power Consumption

Parasitic drain comparable to vehicle baseline (20-50 mA range)
Minimal impact on battery when vehicle is off

Data Flow & Signal Control

Signal Path
1. CAN Bus twisted pair controls access to service OBD2 port
2. Dongle Relay Interruption: Controls whether CAN bus signal reaches the service port
3. OBD2 Port Communication:

Terminating resistors simulate data link presence
Prevents scanner/programmer from detecting open circuit
Dummy port masks actual service port location

Backup System

Spare dongle kept in vehicle as backup
Manufacturer supports up to 3 FOBs
Spare dongle can operate with simple wire connection as failsafe. No relay.

Enhanced Security Features
Additional Layers

Hidden hood release: Prevents easy engine bay access
Smart motion sensor alarm: Integrated into 12V charger socket with wireless siren under hood
Soler Performance Accelerator Disable
Security screws: Prevent dongle disassembly and BCM Security Cover Plate Removal

NOTE: The pair of wires (2 feet length) hanging on the completed harness will not be on your harness. Those wires were for Capricio's Design and connected to the wire leading to pin #15 on the BCM. See picture below. Ignore references to Pin #15 to Starter Relay Coil because that is wrong and Pin #15 DOES NOT control the starter relay, period.

I reused the harness as shown in the final schematic. Remember when I connected to the wire for Pin #15 and removed the dongle, my car shut off entirely, dead. Pin #15 is NOT the Starter control.

IMHO.....GM Chev have a very serious design flaw in the BCM that shuts down the car when Pin #15 is disconnected, open circuit, loose connection, etc.

02-06-2026, 10:18 PM	#1
Roddrz Drives: 2022 Camaro V6 2LT Convertible Join Date: Jul 2021 Location: Calgary, Alberta Posts: 92	CAN Bus Security Dongle Design Guide CAN Bus Security Dongle Design Guide Security Dongle Design Summary Overview A cost-effective DIY security solution ($35 in components) contained in a single OBD2 dongle that prevents vehicle theft by disabling CAN bus access to the OBD2 service port. Design Philosophy Keep your doors unlocked approach: Focuses on preventing key programming rather than preventing window break-ins CAN Bus vulnerability mitigation: Disables source of vulnerability through service port No stock wires or connectors are cut How the Security Dongle Functions Core Mechanism The dongle operates through a "miniature DPDT wireless relay" that controls CAN bus access to the service port: Default State: When unplugged or disarmed, the relay disconnects the CAN bus signal to the service OBD2 port Armed State: User presses the FOB button to activate the relay, connecting the CAN bus to the service port Set and Forget: Once armed, the relay remains latched until power is removed from the dongle or the dongle is unplugged Installation Process Connect the relay control wire to the CAN bus twisted pair that controls access to the service OBD2 port Relay gets it's power by 12V and ground pins from dummy OBD2 port Add 120 Ohm terminating resistors across GMLAN pairs to trick FOB programmer into detecting a data link Solidly tape the Data Link Connector to BCM and tye wrap the connector under the dash Install security plate using security screws over BCM wire connectors Build & Installation Time Harness and Relay Build: 8 hours Security Plate Build: 5 hours Installation: Wire and security plate installation takes approximately 1 hour Total: Approximately 14 hours Parts List ($35 total) 12V Wireless Remote Control Switch: $13.00 Harness: $12 Small OBD2 connector dongle case: $8.00 Benefits & Safety Advantages Security Design Philosophy CAN Bus Protection: Blocks unauthorized key programming through OBD2 service port Dummy Port Concept: Uses a dummy OBD2 port to obscure the actual service port location Physical Barriers: Solid aluminum cover (1/8" thick) over BCM wire connectors with security screws prevents vampire clamp access Operational Advantages No User Friction: Set and forget operation—arm once, no re-arming required until power interruption Integrated Concepts: Combines two proven security methods: "Keep Hope Alive's" Dummy Plug concept Ravelco's anti-theft device principles Compact Design: Smaller form factor dongle case (half previous size, not shown) that fits the wireless relay perfectly, enabling discreet installation Theft Prevention Scenario Even if a thief: Pulls the dongle from the dummy port Finds and accesses the live OBD2 service port Cannot program a new key because CAN bus access is disabled until dongle is reinserted and armed with the FOB However, if they manage to find the OEM OBDII port or vampire clamp onto the BCM wires then they are away to the races. Test Results (1 Year) Performance Validation One Year of Flawless Testing: The concept has been tested and working without failure for a full year Component Reliability: Test parts fit perfectly with a very small case for the wireless relay Relay Durability Analysis Rated Operations: 100,000 minimum operations at heavy load (30VDC, 1 Amp) Actual Usage Estimate: Only 20-40 relay toggles over vehicle service life Margin of Safety: 2,500x safety margin (100,000 rated vs. 40 estimated operations) Holding Current: Only 8 mA when latched (12V / 1440Ω coil resistance) Power Consumption Parasitic drain comparable to vehicle baseline (20-50 mA range) Minimal impact on battery when vehicle is off Data Flow & Signal Control Signal Path 1. CAN Bus twisted pair controls access to service OBD2 port 2. Dongle Relay Interruption: Controls whether CAN bus signal reaches the service port 3. OBD2 Port Communication: Terminating resistors simulate data link presence Prevents scanner/programmer from detecting open circuit Dummy port masks actual service port location Backup System Spare dongle kept in vehicle as backup Manufacturer supports up to 3 FOBs Spare dongle can operate with simple wire connection as failsafe. No relay. Enhanced Security Features Additional Layers Hidden hood release: Prevents easy engine bay access Smart motion sensor alarm: Integrated into 12V charger socket with wireless siren under hood Soler Performance Accelerator Disable Security screws: Prevent dongle disassembly and BCM Security Cover Plate Removal NOTE: The pair of wires (2 feet length) hanging on the completed harness will not be on your harness. Those wires were for Capricio's Design and connected to the wire leading to pin #15 on the BCM. See picture below. Ignore references to Pin #15 to Starter Relay Coil because that is wrong and Pin #15 DOES NOT control the starter relay, period. I reused the harness as shown in the final schematic. Remember when I connected to the wire for Pin #15 and removed the dongle, my car shut off entirely, dead. Pin #15 is NOT the Starter control. IMHO.....GM Chev have a very serious design flaw in the BCM that shuts down the car when Pin #15 is disconnected, open circuit, loose connection, etc. Attached Images Last edited by Roddrz; 02-09-2026 at 11:22 PM.