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DTC codes / U00xx · Network wiring and bus faults / U0024

U0024Low Speed CAN Communication Bus (-) Open

U0024 indicates that the controller area network (CAN) bus has detected an open circuit on the low-speed CAN negative line, which is the return path for differential data communication between modules. The fault is set when a module monitoring the bus sees an expected voltage or signal missing on the CAN low wire, disrupting normal data exchange across the network.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights illuminated on the dashboard, often including the check engine light, ABS, and airbag warnings.
  • Intermittent or complete failure of communication with scan tools for one or more control modules.
  • Erratic operation of electrical accessories such as windows, locks, or climate control due to lost network messages.
  • The vehicle may enter limp mode or refuse to start if critical modules cannot communicate.
  • Often no symptoms besides the warning light if the open is on a non-critical segment of the bus.

Common causes, most likely first

  1. A broken or chafed wire in the CAN low circuit, often at a flex point near a door hinge or under the dash.
  2. Corroded or loose pins in a CAN bus connector, particularly at a module or splice pack.
  3. A failed control module that internally shorts or opens the CAN low line.
  4. Damage from rodent chewing or previous repair work that pinched the harness.
  5. Water intrusion into a connector or module causing corrosion on the CAN low terminal.
  6. A missing or improperly installed terminating resistor in the CAN bus network.

How to diagnose and fix it

  1. Connect a scan tool and record all modules that fail to communicate, then check for other CAN-related codes to narrow the fault to a specific segment.
  2. Inspect the CAN low wire at each module connector for corrosion, pushed-out pins, or loose terminals, starting with the modules that are not communicating.
  3. Measure resistance between CAN low and CAN high at the data link connector (DLC) with the battery disconnected; a reading far from 60 ohms indicates an open or missing termination.
  4. Perform a voltage drop test on the CAN low circuit while wiggling the harness at suspected flex points to find intermittent opens.
  5. Disconnect modules one at a time to see if the bus resistance returns to normal, isolating a faulty module that is loading down the line.
  6. Repair or replace the damaged section of CAN low wiring, using proper crimp and seal techniques, then clear codes and verify communication with all modules.

What a CAN low open really means

  • A single open on the CAN low wire can take down the entire bus because the differential signal relies on both lines being intact, so many modules may appear dead even though only one wire is broken.
  • Technicians often replace a module that fails to communicate when the real problem is a corroded connector pin on the CAN low circuit, so always check connector condition before condemning a module.
  • The code can be set by a module that is not on the main bus but on a sub-network, so consult the wiring diagram for the specific vehicle to locate all CAN low segments.
  • Intermittent U0024 codes are frequently caused by a harness rubbing against a metal edge near the steering column or pedal assembly, which only opens the circuit when the vehicle is moving.
  • A missing or damaged terminating resistor can mimic an open on the CAN low line, so measure resistance at the DLC before cutting into the harness.

Can I keep driving with U0024?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid long trips and be prepared for warning lights or limp mode. If multiple modules are offline or the engine stalls, stop driving and have the vehicle towed to prevent unsafe loss of communication.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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