Code
B2801
HYUNDAI
B — Body
MM CAN Single Line Error
Views:
UK: 20
EN: 29
RU: 16
AI status
Completed
Completed
100%
Causes
- Damaged or chafed CAN single-wire harness (open or short to ground/ignition)
- Poor or corroded connector pins at MM module or other CAN nodes
- Faulty MM (multimedia/monitor) module
- Short to battery or ground in the single-wire CAN line
- Pull-down/pull-up resistor or termination issue
- Intermittent wiring connection due to vibration or water ingress
Symptoms
- Multimedia/infotainment features intermittent or nonfunctional
- Loss of certain CAN-dependent features (audio, screen messages, phone)
- Intermittent communication warnings or multiple related DTCs
- Possible no-start or restricted functions if other modules affected
- Erratic behavior of devices that rely on the single-wire CAN
What to check
- Read and record all related DTCs and freeze-frame data with a full OEM scanner
- Visual inspection of CAN single-wire harness routing, connectors, and grommets for damage or corrosion
- Wiggle test harness and connectors while monitoring live data or DTC status
- Check battery/ground condition and voltage stability (low system voltage can cause bus errors)
- Inspect for recently installed aftermarket devices tied into the wiring
- Consult OEM wiring diagram to identify all nodes on the affected single-wire CAN
Signal parameters
- Recessive (idle) single-wire CAN line voltage approximately mid-rail — verify exact value in OEM manual (commonly ~2.5 V)
- Dominant state pulses pull the line toward low voltage (near 0–1 V) during transmission
- Line should show a clean digital waveform; excessive noise, distorted edges, or missing pulses indicate fault
- Typical low-speed single-wire CAN baud rates vary by model — confirm the correct bitrate with OEM specs before logging
- Open-circuit or short to battery/ground will show steady abnormal voltages (near 0 V for short to ground, near battery voltage for short to B+)
Diagnostic algorithm
- Confirm DTC: Use an OEM-capable scan tool to confirm B2801 and note any additional communication codes; clear codes and attempt to reproduce.
- Visual & Passive Checks: Inspect connectors at MM module, BCM and any intermediate junctions for corrosion, bent pins, water intrusion or loose terminals.
- Measure Idle Voltage: Backprobing the single-wire CAN at the MM connector, measure the idle (recessive) voltage with a DVM and compare to OEM spec.
- Check for Shorts/Opens: With ignition off, measure continuity between CAN line and ground/B+; check resistance between MM CAN pin and other nodes on the same bus using the wiring diagram.
- Wiggle/Load Test: With the system powered and scan tool monitoring the bus, perform a wiggle test on the harness and connectors to see if the fault appears or DTCs set.
- Oscilloscope Capture: If available, use a scope to view waveform integrity while reproducing the fault. Look for missing frames, excessive noise, or incorrect voltage levels.
- Isolate Section: If fault appears intermittent, disconnect suspect nodes one at a time (per OEM safe procedures) to identify which device removal clears the fault.
- Inspect Termination/Pull Components: Verify the presence and correct values of any termination resistors or bus bias/pull resistors specific to the single-wire CAN.
- Repair Wiring/Connector Faults: Repair damaged wiring, replace corroded connectors or pins, and re-seal harness openings as required.
- Module Suspect: If wiring and bus hardware check good and the fault persists when the MM is reconnected, consider replacing or reflashing the MM module per OEM guidance.
- Verify Repair: After repair or module replacement, clear codes and verify normal communication and that B2801 does not return under normal use.
Likely causes
- Loose/corroded connector at the MM unit or at a nearby junction
- Open or short in the single-wire CAN between MM and BCM/other modules
- Failed MM module transmitter/receiver on the single-wire CAN transceiver
- Damaged insulation where harness passes through door hinge or dash
Fault status
Status
MM CAN single-line communication error detected — open/short/intermittent condition on single-wire CAN bus between MM and network nodes.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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