A CAN bus resistance test can quickly reveal missing termination, shorted wiring and basic network-integrity problems. On many high-speed automotive CAN networks, measuring between OBD-II connector pins 6 and 14 should produce approximately 60 ohms when the network is fully powered down.
That number is useful—but it isn’t magic.
A correct 60-ohm reading confirms that the network’s two termination resistors and the wiring between your test point and those resistors appear electrically intact. It does not prove that every module is communicating, every message is valid or every wire behaves correctly while the vehicle is moving.
The multimeter gets a vote. It does not chair the investigation.
Quick answer: What should CAN bus resistance be?
A conventional high-speed CAN network normally uses one 120-ohm terminating resistor at each end of the main bus. Because those resistors are connected in parallel, resistance measured across CAN High and CAN Low is normally close to 60 ohms.
| Resistance reading | Possible meaning |
|---|---|
| Approximately 60 ohms | Both terminating resistors are probably present |
| Approximately 120 ohms | One terminating resistor or one end of the bus may be disconnected |
| Near 0 ohms | CAN High and CAN Low may be shorted together |
| Significantly below 60 ohms | Extra termination, internal module fault or wiring short |
| Significantly above 60 ohms | Open wiring, poor connection or missing termination |
| OL or infinite resistance | Open circuit, inaccessible network or both terminators disconnected |
| Reading changes continuously | Modules may still be awake or the circuit may not be fully isolated |
These values are general diagnostic guidelines. Always compare the result with the manufacturer’s wiring diagram and service procedure.
Modern vehicles may contain several CAN networks, gateways, switches and dynamically controlled termination arrangements. Assuming every car should measure exactly 60.0 ohms at the diagnostic connector is an excellent way to diagnose the wrong network with impressive confidence.
What is a CAN bus?
CAN stands for Controller Area Network. It allows multiple electronic control modules to exchange information over a shared pair of wires.
Depending on the vehicle, the network may connect modules controlling:
- Engine operation
- Automatic transmission
- ABS and stability control
- Electric power steering
- Instrument cluster
- Body electronics
- Airbags
- Four-wheel drive
- Adaptive suspension
- Driver-assistance systems
Instead of running a dedicated wire between every module for every piece of information, CAN allows those modules to transmit digital messages across a common network.
For example, the engine-control module can transmit engine speed once. The transmission, instrument cluster, ABS module and other controllers can then use that information without each requiring a separate RPM wire.
That reduces wiring, although it also means one damaged twisted pair can make several modules begin filing complaints simultaneously.
What are CAN High and CAN Low?
High-speed CAN normally uses two signal wires:
- CAN High, commonly abbreviated CAN-H
- CAN Low, commonly abbreviated CAN-L
The wires are twisted together to help reject electromagnetic interference. The modules interpret the voltage difference between the two circuits rather than relying on one wire alone.
During the network’s recessive state, both lines commonly remain near the same midpoint voltage. During a dominant bit, CAN High rises while CAN Low falls, creating a differential voltage that receiving modules interpret as data.
Actual voltage specifications vary by network and manufacturer. Resistance testing evaluates the network’s passive electrical structure; voltage and waveform testing evaluate its powered operation.
Why does a healthy CAN network measure about 60 ohms?
A conventional high-speed CAN bus uses a 120-ohm resistor at each physical end of its main wiring path.
The resistors absorb signal energy and limit reflections that could corrupt high-speed data. Texas Instruments describes 120-ohm termination at the network endpoints in its CAN bus design documentation, while CSS Electronics’ CAN termination guide explains how the two resistors support signal integrity.
The two resistors are electrically parallel: Rtotal=120+120120×120=60 Ω
This is why a properly terminated, fully powered-down network commonly measures approximately 60 ohms between CAN High and CAN Low.
The terminators may be standalone resistors, but they are often built into modules located near opposite ends of the network. Depending on the vehicle, one may be inside the PCM, ABS module, body-control module, gateway or another controller.
Do not replace a module simply because it contains a terminating resistor. First determine why that resistor is missing from the measured circuit.
Which OBD-II pins carry CAN signals?
On vehicles using ISO 15765-4 high-speed CAN through the standard diagnostic connector:
| OBD-II pin | Standard function |
|---|---|
| Pin 4 | Chassis ground |
| Pin 5 | Signal ground |
| Pin 6 | CAN High |
| Pin 14 | CAN Low |
| Pin 16 | Battery power |
The resistance test is performed between pins 6 and 14.
Do not measure resistance between a CAN circuit and pin 16. Pin 16 carries battery voltage, which is less interested in your diagnostic plan than you might hope.
Manufacturer-controlled pins can carry other networks or signals. Use the vehicle’s wiring diagram before testing nonstandard connector positions.
Tools needed
You will usually need:
- Digital multimeter with an ohms setting
- Correct terminal probes or a breakout box
- Vehicle wiring diagram
- Module-location information
- Scan tool capable of reading all vehicle modules
- Back-probing or terminal-testing equipment approved for automotive connectors
- Oscilloscope for advanced signal diagnosis
A breakout box is preferable to forcing oversized meter probes into the diagnostic connector. Spread terminals can turn a diagnostic test into an additional repair.
If you need a refresher, Pro Street’s How to Use a Multimeter guide covers basic meter setup and measurement practices.
Safety precautions before testing CAN resistance
Never perform an ohms test on a powered circuit.
A multimeter measures resistance by applying a small internal test current. External voltage can produce an inaccurate reading, damage the meter or affect vehicle electronics.
Before testing:
- Park the vehicle safely.
- Switch the ignition off.
- Remove the key or move the key fob away from the vehicle.
- Close or latch doors as required so modules can enter sleep mode.
- Wait the manufacturer-specified shutdown period.
- Disconnect the battery if the service procedure requires it.
- Follow any required battery-registration or memory-preservation procedures.
- Verify the network is powered down before selecting resistance mode.
Some vehicles can wake modules when a door opens, a key approaches or the diagnostic connector is accessed. Others use network gateways that isolate branches when asleep.
Hybrid and electric vehicles require additional high-voltage precautions. Do not disconnect orange high-voltage connectors or probe high-voltage circuits unless you are trained and equipped to follow the manufacturer’s procedure. CAN communication may be low voltage, but the vehicle surrounding it may be considerably less forgiving.
How to test CAN bus resistance at the OBD-II port
Step 1: Perform a complete vehicle scan
Before disconnecting power, scan every available control module.
Record:
- Stored, pending and history codes
- Modules that communicate
- Modules that do not respond
- Network or U-codes
- Freeze-frame information
- Battery-voltage codes
- Recent module replacements or programming
The pattern matters. If several modules report losing communication with one controller, that controller may lack power or ground. If the scan tool cannot communicate with anything, begin with diagnostic-connector power, grounds and network integrity.
Do not clear the codes before recording them. Diagnostic evidence is considerably less useful after it has been ceremonially erased.
Step 2: Locate the diagnostic connector
The 16-pin diagnostic link connector is normally beneath the driver’s side of the dashboard.
Identify the pin positions carefully. Connector diagrams may be illustrated from either the terminal side or wiring side, which reverses the visual orientation.
Verify the view before inserting probes.
Step 3: Power down the network
Switch the ignition off and allow the vehicle’s modules to enter sleep mode. Follow the manufacturer’s instructions regarding battery disconnection and waiting periods.
Confirm that the meter is not seeing voltage across pins 6 and 14 before changing to resistance mode.
Never place the meter in ohms mode on a live network.
Step 4: Set the multimeter to resistance
Select the lowest suitable resistance range or use autoranging.
Touch the meter leads together before testing. The display should show resistance close to zero. If the leads themselves produce measurable resistance, account for that value or use the meter’s relative function.
Step 5: Measure between pins 6 and 14
Place one probe on OBD-II pin 6 and the other on pin 14.
Polarity does not matter for a basic resistance measurement.
Avoid forcing the probes into the connector. Maintain steady contact and observe the reading.
Step 6: Compare the result with specifications
A traditional, intact high-speed CAN bus commonly measures near 60 ohms.
Small variation may be normal because of:
- Resistor tolerance
- Meter accuracy
- Connector resistance
- Temperature
- Network design
- Additional connected circuitry
The service manual gets the final vote. Some vehicles use gateway-controlled branches, multiple CAN buses, split termination or architectures that cannot be evaluated accurately from the generic OBD-II pins alone.
Step 7: Diagnose the reading instead of replacing parts
The reading identifies a direction, not automatically a failed component.
Use the wiring diagram to locate:
- Both terminating resistors
- Gateway modules
- Network splice packs
- Inline connectors
- CAN branches
- Modules on the affected network
- Areas of previous collision or repair work
Then isolate the circuit systematically.
What does a 120-ohm CAN bus reading mean?
A reading near 120 ohms commonly means the meter sees only one of the two terminating resistors.
Possible causes include:
- Open CAN High wire
- Open CAN Low wire
- Disconnected terminating module
- Missing power or ground at a gateway
- Unplugged harness connector
- Corroded splice
- Failed internal terminating resistor
- Network branch isolated by the vehicle’s architecture
Do not immediately install another 120-ohm resistor across the connector. That may restore the resistance reading while leaving an entire section of the network disconnected.
The goal is to find the missing termination path—not make the meter display a prettier number.
What does zero or very low CAN resistance mean?
Resistance near zero may indicate that CAN High and CAN Low are shorted together.
Possible causes include:
- Crushed wiring harness
- Melted insulation
- Water intrusion
- Corroded connector
- Failed module transceiver
- Improper aftermarket wiring
- Incorrect splice repair
- Damaged diagnostic accessory
Disconnect recently added equipment first when appropriate. Alarm systems, remote starters, stereos, trackers, data loggers and poorly installed tuning hardware can all interact with vehicle networks.
Factory wiring occasionally fails. Aftermarket wiring simply enjoys a shorter route to becoming suspicious.
What does a reading below 60 ohms mean?
A reading materially below specification may indicate additional resistance connected in parallel with the original terminators.
Possible causes include:
- An extra terminating resistor
- Aftermarket module with internal termination enabled
- Shorted CAN transceiver
- Moisture inside a connector or module
- Cross-connection with another network
- Incorrect harness repair
Network accessories designed for standalone CAN systems sometimes contain selectable termination. Adding one to an already terminated vehicle network can lower total resistance and distort the signal.
Verify every added controller, gauge, dash, ECU and data-logging device.
What does an open-circuit reading mean?
An OL or infinite-resistance reading means the meter cannot find a complete path between CAN High and CAN Low.
Possible explanations include:
- Both terminating resistors are disconnected
- Both network wires are open
- The diagnostic connector is not directly connected to that CAN bus
- A gateway has isolated the network
- The wrong connector pins are being tested
- A main harness connector is unplugged
- The vehicle uses a different diagnostic architecture
Confirm the connector layout and wiring diagram before dismantling the vehicle in search of two simultaneous resistor failures.
How to isolate a CAN bus wiring fault
If the baseline resistance is incorrect, isolate the network in controlled sections.
A practical process is:
- Obtain the correct network diagram.
- Identify both termination locations.
- Inspect known harness trouble areas.
- Check recent repair or accessory-installation locations.
- Disconnect one approved branch or module at a time.
- Recheck resistance after each change.
- Record what changes the reading.
- Verify module power and grounds before condemning the module.
- Repair wiring using the specified twisted-pair construction.
- Reassemble the network and confirm communication.
Disconnect modules only according to manufacturer instructions. Some connectors contain airbag, high-current or high-voltage circuits alongside network wiring.
If unplugging one module restores resistance to specification, the fault may be inside that module or in its branch wiring. Test both before ordering anything expensive.
Why 60 ohms does not prove the CAN bus is healthy
A network can measure 60 ohms and still fail.
Resistance testing may not identify:
- Intermittent open circuits
- Wiring that fails only with heat or vibration
- CAN High shorted to power
- CAN Low shorted to ground
- Excessive signal noise
- Incorrect network voltage
- Corrupted data
- Module timing faults
- Weak transceivers
- Excessively long or untwisted repairs
- Signal reflections from branch-length problems
- A module that has correct termination but no power
The terminating resistors can remain perfectly intact while a communication circuit misbehaves everywhere else.
If resistance is correct but communication problems remain, continue with voltage, wiring and waveform testing.
When should you use an oscilloscope?
An oscilloscope becomes valuable when the network resistance is correct but faults remain intermittent or communication continues to fail.
A scope can reveal:
- Missing CAN High or CAN Low activity
- Distorted dominant and recessive states
- Electrical noise
- Reflections
- Signal asymmetry
- Intermittent dropouts
- Voltage clipping
- Poor-quality wiring repairs
- A module repeatedly disrupting communication
Scope both CAN High and CAN Low when possible and compare the differential behavior with manufacturer specifications.
Do not assume every strange-looking edge identifies the failed module. Probe location, bandwidth, sample rate, grounding and vehicle network design all affect the displayed waveform.
Common CAN bus diagnostic mistakes
Testing resistance while the network is powered
This produces unreliable readings and may damage test equipment or electronics.
Assuming every vehicle must read exactly 60 ohms
Many do. Some modern gateway-controlled architectures do not provide a simple end-to-end measurement at the diagnostic connector.
Replacing a noncommunicating module without checking power and ground
A silent module may simply be unpowered. Test its fuses, feeds and grounds before blaming its internal electronics.
Adding a resistor to correct a 120-ohm reading
This can mask the missing half of the network without repairing it.
Using piercing probes unnecessarily
Puncturing insulation creates a path for corrosion. Use approved back-probing, breakout leads or connector test adapters.
Untwisting CAN wiring during repair
Maintain the original conductor type, twist rate, routing and splice method. Long untwisted sections make the network more vulnerable to interference and reflections.
Clearing every U-code immediately
Communication codes can show which modules remained online and which one disappeared. Record the evidence before removing it.
Frequently asked questions
Can I test CAN bus resistance with the battery connected?
Resistance should only be measured on a fully powered-down circuit. Follow the vehicle manufacturer’s procedure for battery disconnection, module sleep time and memory preservation.
Why do two 120-ohm resistors measure 60 ohms?
The resistors are connected in parallel across CAN High and CAN Low. Two equal 120-ohm resistors in parallel produce 60 ohms of total resistance.
Does 120 ohms prove that a terminating resistor failed?
No. It means only one termination path is visible from the test point. The other path could be isolated by open wiring, a disconnected connector, a gateway or a module containing the second resistor.
Can a bad module pull down the CAN bus?
Yes. A failed CAN transceiver can short or distort one or both network circuits. Verify the module’s wiring, connector, power and grounds before replacement.
Can aftermarket electronics cause CAN communication faults?
Yes. Incorrectly connected alarms, remote starters, tuning devices, digital dashboards and data loggers may short the network, introduce termination or produce signal-quality problems.
Can I check CAN resistance on pins other than 6 and 14?
Only with the correct vehicle wiring diagram. Pins 6 and 14 are standardized for the legislated high-speed CAN diagnostic network, while manufacturers may use other pins for proprietary networks.
Will a generic code reader diagnose a CAN bus fault?
A basic reader may only communicate with the powertrain controller. A capable scan tool that surveys all modules is much more useful for determining which sections of the network remain operational.
Should I replace the PCM if the CAN resistance is incorrect?
Not without circuit isolation and complete power, ground and wiring tests. The PCM is one possible network participant—not the official scapegoat for every confusing electrical problem.
The bottom line
To test high-speed CAN bus resistance at the OBD-II port, fully power down the network and measure between pins 6 and 14. A conventional network with two functioning 120-ohm terminating resistors should read approximately 60 ohms.
A reading near 120 ohms points toward a missing termination path. Very low resistance suggests a short or unwanted parallel resistance. An open reading indicates that the meter cannot see a complete path across the network.
Use that result to guide further testing—not to authorize immediate module replacement. Combine resistance measurements with a complete module scan, wiring diagrams, power and ground checks, voltage testing and oscilloscope analysis when necessary.
For related electrical procedures, see: