How to Identify CAN Bus Wiring in a Car

The Short Answer

On most cars sold in the US from the 2008 model year onward, the easiest place to start is the OBD-II diagnostic connector under the dashboard. Pin 6 carries CAN High and pin 14 carries CAN Low. Trace those two wires back from the connector and you will typically find a twisted pair of small-gauge wires. They are often the same base color with different stripes, or two closely related colors. The pair continues to modules such as the engine controller, transmission controller, ABS unit and instrument cluster, often by way of a gateway module.

Appearance alone does not confirm a CAN wire. A reliable identification combines three checks. First, the wire's position and pin assignment must match the factory wiring diagram for your exact vehicle. Second, the two wires must be twisted together along their run. Third, the electrical readings must fit. With power removed, the two wires should measure about 60 ohms to each other. With the ignition on, each wire should sit near 2.5 volts to ground. A pair that passes all three checks is almost certainly a high-speed CAN bus.

How a CAN Bus Is Wired

CAN (Controller Area Network) sends data as a voltage difference between two wires rather than as a voltage on a single wire. When the bus is idle, both wires rest at about 2.5 volts. When a module transmits, CAN High rises toward roughly 3.5 volts and CAN Low falls toward roughly 1.5 volts. Receiving modules read the difference between the two. Twisting the wires together means electrical noise from ignition coils, motors and alternators affects both wires almost equally, so the difference stays clean. This is why the twist is such a useful visual clue.

A high-speed CAN bus has a 120-ohm termination resistor at each physical end. These resistors are usually built into two of the modules rather than mounted as separate parts. The two resistors are in parallel, so a healthy bus measures about 60 ohms between CAN High and CAN Low. Modules connect along the bus directly or through splice points and junction connectors. The data wires carry almost no current. Each module gets power and ground through separate circuits, so a blown fuse or the wrong fuse rating affects a module's power feed, not the CAN wires.

What CAN Bus Wiring Colors Tell You

There is no universal color code for CAN bus wiring. Many manufacturers use a matched pair, such as one base color with two different tracer stripes, so the two wires look related. Some European manufacturers have used an orange base color with a different stripe on each wire. Others use completely unrelated colors. A single vehicle often has several CAN networks, and each one may use its own color pair. A wire can also change color where it passes through an inline connector.

Treat color as a hint that points you toward a candidate pair. Use the wiring diagram, the pin numbers at the connector, and the twist to confirm it. A color chart copied from a different model, model year or trim level can easily send you to the wrong circuit.

Vehicle Differences That Change the Answer

The 60-ohm and 2.5-volt guidelines apply to high-speed CAN, which handles powertrain, chassis and diagnostic traffic in most modern vehicles. Some older vehicles, particularly some European models, used a low-speed fault-tolerant CAN for body functions. That network has different termination and voltage behavior, so the standard tests do not apply to it. Some GM vehicles have used a single-wire CAN for body and comfort modules. It is one wire, not a twisted pair. Many cars also use LIN bus for switches, mirrors and sensors. LIN is a single wire whose voltage sits near system voltage when idle, so it is easy to tell apart from CAN once you measure it.

Not every twisted pair is CAN. FlexRay, automotive Ethernet, speaker leads and some shielded sensor circuits, such as crankshaft or wheel speed sensor wiring, can also be twisted. On vehicles with a gateway module, the OBD-II port may connect only to a diagnostic branch. Other CAN networks behind the gateway will not show up at pins 6 and 14. In those cases you need the wiring diagram's network topology page to find which modules sit on which bus.

Hybrids and EVs: 12-Volt Network Versus High Voltage

Hybrids and electric vehicles have two separate electrical systems. The 12-volt starter or auxiliary battery powers the control modules, lighting and the CAN network, just as in a conventional car. The traction system runs at several hundred volts. Its cables are thick and usually sheathed in orange insulation or conduit. A thin data wire with an orange stripe is not the same thing as an orange high-voltage cable, but never probe, pierce or unclip anything orange or anything labeled as high voltage.

Disconnecting the negative 12-volt battery terminal removes power from the CAN network, but it does not de-energize the traction battery or its cables. Isolating the high-voltage system requires the manufacturer's service disconnect procedure, insulated tools and protective equipment. That job belongs with a trained technician. For CAN identification you should only need the low-voltage side, usually at the diagnostic connector or at module connectors inside the cabin.

Confirming the Pair With a Multimeter

Start with the factory wiring diagram for your exact vehicle, matched by VIN or model year and trim. Then do a resistance check. Switch the ignition off, remove the key or move the key fob away, and wait several minutes so the modules go to sleep. Disconnect the negative battery terminal. Measure resistance between pins 6 and 14 at the OBD-II connector, or between the suspected wires at a module connector.

About 60 ohms is normal. About 120 ohms suggests one termination resistor is missing or the circuit is open between it and your test point. A reading near zero indicates a short between the two wires. An open circuit or very high reading suggests a break in the wiring or both terminations missing.

For a voltage check, reconnect the battery and turn the ignition on. Measure each wire to ground, using pin 4 or 5 at the diagnostic connector. On an active bus, a typical meter shows CAN High slightly above 2.5 volts and CAN Low slightly below it. A reading near zero or near full system voltage points to a short to ground or to power. A multimeter only shows the average voltage. Viewing the actual signal requires an oscilloscope.

Practical Precautions Near the Network

Back-probe connectors from the wire side with thin probes instead of piercing insulation, because pierced insulation lets in moisture and corrosion. Do not use a test light or a powered circuit tester on CAN wires. Either can load the bus, disrupt communication or damage a module transceiver. Avoid tapping aftermarket remote starters, trackers or interfaces into the bus without the correct diagram. A poor connection can cause communication faults, or keep modules awake and create a parasitic draw that drains the battery overnight.

If a CAN wire is damaged, the repair should keep the twist as close to the connector as possible, use soldered or sealed crimp splices, and include proper heat-shrink protection. Long untwisted sections or loose splices can let interference in and cause intermittent faults that are hard to trace.

Limitations and Next Step

The values in this guide are typical for high-speed CAN, not guaranteed for every vehicle. Network layout, wire colors, termination locations and gateway behavior differ by manufacturer and model year. A multimeter can confirm that a pair is wired and powered correctly, but it cannot show corrupted messages, a module flooding the bus or intermittent dropouts. Those faults need a scan tool that reads network communication codes, which usually begin with U, or an oscilloscope.

Your next step is to get the factory wiring diagram and network topology for your exact vehicle before tracing or repairing anything. Hand the job to a qualified technician if the work involves high-voltage components, airbag circuits or modules that need programming after replacement. The same applies if communication faults remain after the basic resistance and voltage checks pass.