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Home / DTC / C1649 — CAN time-out ECM for SCC (Check ECM)

C1649 — CAN time-out ECM for SCC (Check ECM)

Detailed page for trouble code C1649.

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C1649

HYUNDAI C — Chassis

CAN time-out ECM for SCC (Check ECM)

Brand: HYUNDAI
Type: C — Chassis
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Intermittent or permanent break in CAN bus wiring between ECM and SCC
  • Short to battery or ground on CAN_H or CAN_L
  • Missing or bad CAN termination resistor(s)
  • Poor module power or ground at ECM or SCC
  • Faulty ECM or SCC module hardware or internal CAN transceiver
  • Corroded or loose connectors at modules or in-line junctions

Symptoms

  • Cruise control or Smart Cruise functions disabled or inoperative
  • Warning lamp(s) such as ABS, ESC, or cruise/information messages on dash
  • Inability to communicate with SCC module via scan tool (no data or intermittent)
  • Stored communication-related U/C codes alongside C1649
  • Vehicle may enter limp or degraded mode if related systems depend on SCC/ECM messages

What to check

  • Check for other stored U or C codes that indicate network problems (U0100, U0073, etc.)
  • Visually inspect CAN wiring, connectors, and junctions between ECM and SCC for damage or corrosion
  • Verify battery voltage and inspect power/ground connections at ECM and SCC
  • Use a scan tool to see live CAN messages and confirm SCC and ECM presence and message rates
  • Measure CAN_H and CAN_L voltages with key ON, engine OFF (recessive ~2.5 V common-mode; differential ~0 V)
  • Check termination resistance between CAN_H and CAN_L with power off (~60 ohms for two 120-ohm terminators in parallel)

Signal parameters

  • CAN_H voltage (key ON, engine OFF): ~2.5 V (idle recessive), ~3.5 V (dominant)
  • CAN_L voltage (key ON, engine OFF): ~2.5 V (idle recessive), ~1.5 V (dominant)
  • Differential voltage CAN_H - CAN_L during idle and active messages
  • Message ID and frequency for ECM and SCC frames (compare to known values or other vehicles)
  • Bus load % and packet error/frame error counters (if scanner/scope provides)
  • Termination resistance between CAN_H and CAN_L (~60 ohms total)

Diagnostic algorithm

  1. Connect a capable scan tool and read all stored codes in all modules. Note any related U or C codes that indicate network issues.
  2. Record live data and presence of ECM and SCC modules. Note whether SCC appears / drops out or shows no messages.
  3. Visually inspect connectors and wiring to ECM and SCC for damage, corrosion, bent pins, or loose terminals. Repair any physical damage.
  4. With ignition ON, measure CAN_H and CAN_L voltages at a convenient connector. Confirm idle voltages ~2.5 V and observe for noise or stuck dominant state.
  5. With vehicle power OFF, measure resistance between CAN_H and CAN_L at a convenient splice or connector. Expect ~60 ohms (two 120-ohm terminators in parallel). Replace missing/incorrect terminators.
  6. Check module power and ground: measure battery voltage at module power pin and verify low-resistance ground to chassis. Repair poor power/ground connections.
  7. Perform wiggle / flex tests on harness while monitoring live data to reproduce the timeout and locate an intermittent break.
  8. If wiring, connectors, power, and termination are good, use an oscilloscope to capture CAN frames and look for corrupted frames, excessive errors, or lack of expected ECM messages to SCC. Compare message IDs and timing to specifications if available.
  9. If testing isolates a specific module (ECM or SCC) as not transmitting or having internal transceiver failure, verify with a known-good module or bench test before replacement. Replace the faulty module only after confirming with thorough testing.
  10. After repairs, clear codes and perform road/test cycles to confirm the DTC does not return and communication is stable.

Likely causes

  • Damaged CAN wiring harness (chafing, pinched, rodent damage) between ECM and SCC
  • Loose or corroded connector pin at SCC or ECM causing intermittent contact
  • Open or high-resistance ground at SCC or ECM module
  • Missing/failed 120 ohm termination resistor or incorrect termination (should see ~60 ohms between CAN_H and CAN_L at rest)
  • Failed CAN transceiver inside ECM or SCC (less common)

Fault status

⚠️ Status
CAN communication timeout detected between ECM and SCC — SCC did not receive expected ECM messages within timeout window. Check CAN bus wiring, power/ground, termination, and module communication.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5 - 3.0 hours

Similar codes

U0100 U0073 U0121 C1648 C1650
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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