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Home / DTC / P1221 — CAN Communication ETC Or ETS Interrupted

P1221 — CAN Communication ETC Or ETS Interrupted

Detailed page for trouble code P1221.

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Code

P1221

MERCEDES-BENZ P — Powertrain

CAN Communication ETC Or ETS Interrupted

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Damaged or chafed CAN wiring between modules
  • Loose, corroded or damaged connector at ETC or ETS module
  • Open or short on CAN_H or CAN_L (to ground or battery)
  • Faulty module (ETC or ETS)
  • Failed/missing CAN bus termination resistor(s)
  • Low battery or poor power/ground to one or both modules

Symptoms

  • Check Engine light or other warning lamp illuminated
  • Reduced engine power / limp-home mode / poor throttle response
  • Intermittent or total loss of drive-by-wire throttle operation
  • Related systems showing communication faults on scan tool
  • Possible engine stall, surging or hesitation
  • No live data or invalid values from one of the affected modules

What to check

  • Read all stored and pending codes from all modules; note time stamps and additional U-codes
  • Check battery voltage and charging system at rest and under cranking
  • Inspect fuses and relays for the ETC/ETS circuits
  • Visually inspect connectors and wiring at ETC and ETS modules for corrosion, damage or loose pins
  • Measure resistance across CAN_H and CAN_L (expected ~60 ohms for two 120Ω terminators in parallel)
  • Backprobe CAN_H and CAN_L with meter/oscilloscope to verify voltage levels and activity

Signal parameters

  • Idle (recessive) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
  • Dominant bit: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approximate)
  • Bus termination: ~60 Ω total (two 120 Ω terminators in parallel)
  • Common CAN bus speeds: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific rate)
  • Oscilloscope should show clean differential waveform with no excessive noise or collisions

Diagnostic algorithm

  1. Connect a full-feature scan tool, record P1221 and any other U/P codes and freeze frame data.
  2. Check battery voltage and fuses/relays that supply ETC/ETS; repair as needed.
  3. Visually inspect and reseat connectors at the ETC and ETS modules; look for bent pins, corrosion, or moisture.
  4. Measure CAN bus resistance between CAN_H and CAN_L with ignition off; compare to expected ~60 Ω.
  5. With ignition on, monitor CAN_H and CAN_L with a scope or logic analyzer to confirm normal voltages and traffic; look for dominant state stuck or missing activity.
  6. If bus shows noise/short, isolate sections by disconnecting modules one at a time and re-checking bus behavior to locate the faulted node or harness segment.
  7. Repair wiring, connectors, or grounding faults found; replace any damaged termination resistor(s).
  8. If wiring and power/grounds are good but communication still fails, swap or bench-test suspect module(s) per manufacturer procedure or replace module following programming instructions.
  9. Clear codes, test drive, and verify the fault does not return. If intermittent, monitor for recurrence and inspect areas subject to movement/flexing.

Likely causes

  • Loose or corroded connector at throttle control module
  • Broken/chafed CAN wiring harness where it flexes or rubs
  • CAN bus short to battery or ground (after wiring damage)
  • Faulty ETC or ETS control module
  • Missing/failed terminating resistor or bus strapped open

Fault status

⚠️ Status
CAN communication between ETC and ETS interrupted — one or both modules not sending/receiving messages. May cause reduced throttle control or limp mode.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0073 U0121 U0140 P1220
856

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