Accessing CAN bus data has traditionally required either a diagnostic connector or a direct electrical connection to the CAN-H and CAN-L lines. This applies equally to classical CAN networks as well as higher-layer protocols such as SAE J1939, which is built on top of CAN. While effective, both approaches introduce potential risks: physical modification of wiring harnesses, accidental network disturbances, and warranty or compliance concerns.
Contactless CAN bus readers address these issues by allowing passive observation of CAN traffic without making an electrical connection. Because SAE J1939 communication uses standard CAN physical and data-link layers, contactless CAN readers can also be used to observe SAE J1939 traffic. One example of this technology is the CANCrocodile from Copperhill Technologies, designed specifically for non-intrusive CAN and SAE J1939 monitoring.
What Is a Contactless CAN Bus Reader?
A contactless CAN bus reader captures CAN traffic by inductively coupling to the electromagnetic field generated by the twisted CAN-H and CAN-L conductors. Since SAE J1939 uses the same physical CAN wiring, J1939 messages are captured in the same manner. The device clamps around the insulated cable and “listens” to traffic on the bus without piercing insulation or electrically loading the network.
Because there is no galvanic connection to the CAN lines, the reader operates purely as a passive monitoring device.
How the CANCrocodile Works
The CANCrocodile is designed for listen-only CAN operation. This includes passive monitoring of higher-layer protocols such as SAE J1939 that are transported over CAN. Once clamped around the CAN twisted pair, it detects voltage transitions on the bus and reconstructs CAN frames, including SAE J1939 Parameter Group Numbers (PGNs), for external logging or analysis tools.
Key characteristics include:
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No electrical connection to CAN-H or CAN-L
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No CAN or SAE J1939 message transmission or arbitration participation
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No modification of the original network topology
This architecture makes the CANCrocodile particularly well suited for observation, logging, and validation tasks where preserving the original system behavior is critical.
Advantages of a Contactless Approach
Non-Invasive Access
Because the CAN or SAE J1939 wiring remains untouched, the risk of introducing intermittent faults, insulation damage, or long-term reliability issues is significantly reduced. This is especially valuable in tightly packed or environmentally exposed harnesses.
Network Safety
Since the device does not transmit messages or acknowledge frames, it cannot interfere with arbitration, bus timing, ECU behavior, or SAE J1939 communication. This makes it suitable for use on production vehicles, industrial machinery, and safety-critical systems where network integrity is paramount.
Faster Deployment
Installation requires no connectors, breakout cables, or pin-out documentation. In many cases, CAN or SAE J1939 data acquisition can begin within minutes of identifying the CAN twisted pair.
Warranty and Compliance Considerations
In applications where harness modification is restricted or prohibited, a contactless reader can be used on CAN and SAE J1939 systems without violating OEM guidelines or internal compliance rules.
Typical Use Cases
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Field diagnostics and troubleshooting on CAN and SAE J1939 networks
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Long-term CAN or SAE J1939 data logging
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Validation and verification during system testing
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Educational and training environments involving J1939-heavy-duty vehicle networks
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Temporary instrumentation of customer or fleet vehicles
Limitations to Understand
Contactless CAN readers are not a replacement for full diagnostic interfaces in every scenario. Because the CANCrocodile is listen-only, it cannot:
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Transmit diagnostic requests (including SAE J1939 diagnostic messages)
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Inject test messages
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Perform ECU configuration or flashing
For active diagnostics or bidirectional communication on CAN or SAE J1939 networks, a traditional CAN interface is still required.
When to Choose the CANCrocodile
The CANCrocodile is best suited for engineers and technicians who need reliable access to CAN or SAE J1939 data without altering the system under test. It is particularly effective when the priority is observation rather than control.
For organizations focused on system safety, rapid deployment, and non-intrusive measurement of CAN and SAE J1939 networks, contactless CAN monitoring provides a practical and professional solution. More information…
The Car Hacker’s Handbook
The Car Hacker’s Handbook offers a deep and practical exploration of the computer systems, embedded software, and communication networks that power today’s vehicles. It begins by breaking down common automotive vulnerabilities and explaining how electronic control units communicate over the CAN bus and other internal networks. Once you understand how vehicle systems exchange data, the book guides you through real-world techniques for intercepting traffic and executing targeted attacks, including tracking vehicles, unlocking doors, disrupting engine behavior, flooding networks, and more.
Emphasizing low-cost, open-source tools such as Metasploit, Wireshark, Kayak, can-utils, and ChipWhisperer, the book shows you how to build realistic threat models, reverse engineer CAN messages, exploit diagnostic and logging interfaces, hack ECU firmware, and inject attacks through infotainment and vehicle-to-vehicle communication systems. More information…
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