Code
B280200
HYUNDAI
B — Body
MM CAN Limp Home Status
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EN: 22
RU: 18
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Causes
- Intermittent or permanent loss of CAN communication between MM and other modules
- Damaged or corroded CAN wiring, connectors, or pinouts
- Failed CAN transceiver or MM control module
- Missing or failed power supply or ground to the MM module
- Incorrect or missing termination (open/shorted 120 Ω resistors or wiring)
- Electrical interference or short to battery/ground on CAN_H or CAN_L
Symptoms
- Warning message or icon indicating limp home or reduced power
- Reduced engine power, limited top speed, or transmission hold
- Loss of certain instrument cluster data or disabled functions
- Multiple communication-related DTCs present (U-codes)
- Intermittent start/no-start conditions
- MIL/Check Engine lamp illuminated
What to check
- Read all stored and pending DTCs from all control modules; save freeze frame and freeze data
- Visually inspect CAN wiring harness, connectors and junctions for damage, corrosion, water intrusion
- Check MM module power and ground voltages and continuity to battery and chassis ground
- Verify fuses and relays related to MM power are present and functional
- Measure CAN_H and CAN_L voltages with ignition on (engine off) using a DMM and compare with expected values
- Measure termination resistance between CAN_H and CAN_L with ignition off (expect ~60 Ω across the bus)
Signal parameters
- Typical CAN idle voltages (ignition ON, no dominant): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each relative to ground)
- Dominant state (logic 0): CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Recessive state (logic 1): both lines ≈ 2.5 V (differential ≈ 0 V)
- Termination resistance across CAN_H and CAN_L with key off: ≈ 60 Ω (two 120 Ω terminators in parallel)
- Typical bus traffic: periodic diagnostic and control messages; flooding or absence of expected messages indicates fault
Diagnostic algorithm
- Connect an OBD-II scan tool and record all DTCs from all modules. Note time stamps and freeze frame data.
- Confirm symptom and attempt to communicate with the MM module. Note whether the module responds or is BUS-OFF.
- Visually inspect connectors at the MM module, harness routes, and common splice/junction points for corrosion, damage, or water entry. Repair or secure connectors as needed.
- Verify MM module supply and ground: measure battery voltage at the module power pin(s) and check continuity to chassis ground. Repair any open/poor grounds.
- Check related fuses and relays; replace if blown or intermittent.
- With ignition ON, measure CAN_H and CAN_L at the MM module connector with a DMM. Compare to expected idle voltages. If stuck high/low, isolate wiring.
- Measure termination resistance across CAN_H and CAN_L with ignition OFF (expect ~60 Ω). If open or very low, isolate and repair wiring or replace missing terminator.
- Use an oscilloscope to examine CAN waveforms for noise, missing edges, excessive bit errors, or a stuck dominant level. Identify which segment/source causes disturbance by probing at different nodes.
- Disconnect suspected faulty module(s) one at a time (if safe and manufacturer allows) to see if the bus returns to normal communication. Replace or repair the failing module/harness found.
- After repairs, clear codes, perform relearn or initialization procedures if required, then road test and re-scan to confirm the fault does not return.
- Note: If diagnostics require module replacement, confirm root cause (often harness or ground) before replacing modules to avoid repeat failures.
Likely causes
- Corroded connector at MM module or junctions
- Open/short in CAN_H or CAN_L wiring (abrasion, rodent damage, chafing)
- Bad ground or battery fuse feeding the MM module
- Failed MM module CAN transceiver
- Missing/failed bus termination (one or both 120 Ω resistors)
- Another module creating BUS-off condition or flooding messages
Fault status
Status
MM CAN Limp Home Status — Motor Management module detected CAN communication fault and entered limp-home/reduced operation mode.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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