C28B0 – CAN signal fault FR_CMR (Hyundai)

Hyundai-specific code — factory diagnostic data

C28B0 means the Hyundai IONIQ 5 has lost a reliable CAN communication signal that the ADAS system expects. You may notice driver-assist features disable, warnings appear, or functions act inconsistent. According to Hyundai factory diagnostic data, this code indicates a “CAN signal fault FR_CMR” stored by the ADAS_D (ADAS Driving) module. In plain terms, ADAS_D cannot consistently see or trust the FR_CMR message on the CAN network. That matters because ADAS features depend on timely, valid network messages. This code points you to a communication problem first, not a failed camera or sensor.

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C28B0 Quick Answer

C28B0 on Hyundai vehicles means ADAS_D detected a CAN signal fault involving the FR_CMR message/source. Diagnose CAN network integrity and the FR_CMR module power/ground and connectors before replacing any ADAS component.

What Does C28B0 Mean?

Official definition: “CAN signal fault FR_CMR.” The ADAS_D (ADAS Driving) module set this code because it did not receive the FR_CMR CAN message correctly, consistently, or within expected timing. In practice, ADAS_D may shut down or limit driver-assist functions because it cannot confirm required inputs.

What the module checks and why it matters: ADAS_D monitors CAN message presence, message timing, and plausibility for the FR_CMR-related communication. It does not “see” the physical wire directly. It sees missing, corrupted, delayed, or implausible data on the network. This matters for diagnosis because you must confirm network health, power/ground stability, and connector condition. A single bad splice, weak ground, or intermittent connector can mimic a failed module.

Theory of Operation

Under normal conditions, the IONIQ 5 ADAS system uses CAN networks to share sensor and control data between modules. ADAS_D expects specific messages at consistent intervals. Those messages let it coordinate functions like lane support, collision avoidance support, and related warnings.

C28B0 sets when ADAS_D cannot validate the FR_CMR communication. A dropout can come from a wiring fault, high resistance at a connector, unstable module power or ground, or bus-level interference. Timing matters on ADAS networks. Even brief interruptions can trigger a fault and force a feature shutdown.

Symptoms

You will usually see driver-assist warnings and scan-tool communication clues first.

• Scan tool behavior ADAS_D may show FR_CMR-related data missing, a module may appear offline, or communication may drop in and out during a full vehicle scan
• ADAS warning Driver-assist warnings illuminate and some assistance features disable or become unavailable
• Lane functions Lane-related support may not engage or may cancel shortly after activation
• Forward safety features Forward collision-related assistance may display limited operation messages
• Intermittent operation Features work after a restart, then fail again after driving or vibration
• Multiple network DTCs Other chassis or ADAS modules may store CAN-related codes alongside C28B0
• Event-related trigger The fault may appear after body work, windshield area service, or connector disturbance near ADAS components

Common Causes

• CAN bus open circuit on CAN-H or CAN-L: A break in either conductor prevents the ADAS_D module from receiving the FR_CMR message, so it logs a CAN signal fault.
• CAN bus short to ground: Chafing or water intrusion can pull a CAN line low, which collapses differential signaling and stops valid message decoding.
• CAN bus short to battery (B+): A rubbed-through wire can force a CAN line high, which distorts the waveform and causes frame errors or total loss of communication.
• High resistance at a connector or splice: Corrosion or loose terminals add resistance and create intermittent dropouts that look like an erratic or missing FR_CMR signal.
• Poor module power or ground at ADAS_D: A weak feed or ground shifts module logic levels and can make the network transceiver reset or stop communicating.
• Termination or network topology fault: A missing or incorrect terminating path on the Hyundai CAN network causes reflections and intermittent message loss under load.
• FR_CMR node offline or rebooting: The camera-related sender for FR_CMR may lose power, lose ground, or reset, which makes its CAN message disappear.
• Aftermarket wiring or recent body/ADAS repair influence: Added accessories or harness pinches near the front harness can disturb CAN integrity and trigger this specific message fault.

Diagnosis Steps

Use a scan tool that can access Hyundai ADAS_D (ADAS Driving) data and run a full network scan. Have a DVOM, back-probing tools, and wiring repair supplies ready. A 2-channel oscilloscope helps confirm CAN waveform quality. Plan for safe ignition cycling and battery disconnect procedures to protect modules during resistance checks.

1. Confirm DTC C28B0 in ADAS_D and record all related DTCs across modules. Save freeze frame data. For this CAN signal fault, focus on ignition state, vehicle speed, battery voltage, and any companion CAN or camera/ADAS codes.
2. Run a complete network scan and verify ADAS_D appears online. Also check whether the module that transmits FR_CMR appears online. If either module drops out, treat it as a network or power issue first.
3. Check fuses and power distribution for ADAS_D and the suspected FR_CMR sender circuit paths. Do this before probing module connectors. Confirm the correct fuse feeds carry load and do not just pass a continuity check.
4. Verify ADAS_D power and grounds with voltage-drop testing under load. Command an ADAS-related function or keep the ignition ON to load the circuit. Measure ground drop to battery negative and hold it under 0.1V while operating.
5. Inspect harness routing and connectors tied to the front ADAS/camera network path. Look for pinched loom, water tracks, backed-out terminals, and green corrosion. Pay attention to areas disturbed by bumper, windshield, or front-end service.
6. With the ignition ON, check CAN bias at an accessible connector for the involved CAN pair. Measure each CAN line to ground with the circuit powered, because bias only exists when modules are awake. A healthy network typically sits near 2.5V on both lines.
7. If the scan tool shows the module offline or communication unstable, perform a CAN resistance check. Turn ignition OFF, disconnect the battery, then measure resistance between CAN-H and CAN-L at an accessible module connector. Expect about 60 ohms on a healthy bus; readings near 120 ohms or OL point to an open or missing termination.
8. Wiggle-test the harness while watching live data and network status on the scan tool. Use a scan tool snapshot to capture the moment the fault occurs during the wiggle or a controlled road test. Freeze frame shows when the code set; a snapshot captures intermittent dropouts you create during diagnosis.
9. If resistance and bias look correct, use a scope to view CAN-H and CAN-L under normal operation. Look for clipped peaks, heavy noise, or a flat line during the moment FR_CMR drops. Compare to a known-good segment if Hyundai service information provides access points.
10. After repairs, clear codes and perform an ignition cycle and road test. Confirm ADAS_D receives the FR_CMR-related data without dropouts. Recheck for pending versus confirmed status, because some monitors may store pending first and confirm on a second drive cycle, while a hard CCM-type communication fault often returns immediately at key-on.

Professional tip: Do not trust continuity checks on CAN wiring. Corrosion can pass continuity and still kill data. Always combine voltage-drop testing on powers/grounds with powered bias checks and an ignition-OFF resistance test. When C28B0 includes an FTB suffix like -86, use it as direction for the fault type, then prove the condition with measurements before you touch any module.

Possible Fixes

• Repair CAN-H/CAN-L open or short: Restore twisted-pair integrity, correct routing, and proper terminal tension at the exact fault location.
• Clean and correct connector/terminal issues: Remove corrosion, repair damaged pins, and secure locking tabs to prevent intermittent FR_CMR message loss.
• Restore ADAS_D or sender module power/ground integrity: Repair fuse feed issues, splice resistance, or ground points verified by voltage-drop testing under load.
• Correct termination or network splice faults: Repair damaged splices or miswired segments that change bus resistance away from the expected value.
• Rework wiring affected by recent repairs or accessories: Remove CAN taps, correct improper splices, and isolate aftermarket wiring that disturbs the Hyundai CAN network.
• Replace a module only after proof: If the FR_CMR sender or ADAS_D repeatedly resets or drops off the bus with verified power/ground and proven-good CAN lines, replace the confirmed failed module and complete coding/calibration as required.

Can I Still Drive With C28B0?

You can usually drive with C28B0, but you should treat it as an ADAS reliability warning. On a Hyundai IONIQ 5, the ADAS_D (ADAS Driving) module sets this code when it cannot trust CAN communication for the FR_CMR message path. That can disable or degrade driver-assist features without affecting basic propulsion. Plan for reduced assistance. Expect functions like forward safety features, adaptive cruise, lane functions, or related warnings to appear, depending on Hyundai platform configuration. Drive conservatively and leave extra stopping distance. Avoid relying on any ADAS feature until you confirm proper operation after repairs. If the vehicle also shows multiple CAN or power supply codes, stop driving and diagnose immediately.

How Serious Is This Code?

C28B0 ranges from inconvenient to safety-relevant. It stays closer to an inconvenience when only a single network DTC appears and ADAS features simply turn off. It becomes more serious when the fault repeats quickly, sets multiple communication codes, or causes intermittent ADAS behavior. Erratic assistance can surprise the driver. That raises risk more than a clean disable. Because this code sits in the ADAS_D module, repairs can require calibration or initialization if you replace any ADAS module or sensor tied to that CAN message path. Do not return the vehicle with ADAS features enabled until you confirm no recurring DTCs and the system passes self-checks.

Common Misdiagnoses

Technicians often replace a camera or radar assembly because the label says FR_CMR. That skips the required network checks. C28B0 only tells you the module sees a CAN signal fault, not a failed sensor. Another common miss involves ignoring the FTB suffix. For example, an FTB -86 subtype like 31 (No Signal) points you toward loss of message presence, not a “bad image.” Shops also chase the wrong bus because other modules still communicate. A partial CAN fault can isolate only one branch. Avoid wasted spending by confirming power and ground integrity under load, checking connector pin fit and water entry, and verifying message presence with a capable scan tool before condemning any ADAS component.

Most Likely Fix

The most frequently confirmed repair direction involves restoring CAN network integrity for the FR_CMR message path. That usually means fixing high resistance, poor terminal tension, corrosion, or harness damage at an in-line connector or at the ADAS_D module connector. The second common direction involves correcting a power or ground issue that causes the source module to drop offline, which then looks like “No Signal” on. Treat module replacement as a last step. If you replace any ADAS-related module or sensor, plan on Hyundai-specific setup, including coding and calibration, before you consider the vehicle safe to release.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a sensor, a module, or the labor needed to diagnose the fault correctly.

Last updated: April 10, 2026