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Home / DTC / U0615 — Lost Communication With Engine Coolant Bypass Valve A

U0615 — Lost Communication With Engine Coolant Bypass Valve A

Detailed page for trouble code U0615.

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Code

U0615

Generic U — Network/User

Lost Communication With Engine Coolant Bypass Valve A

Brand: Generic
Type: U — Network/User
Views: UK: 15 EN: 29 RU: 23
AI status
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ready
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Page language: EN

Causes

  • Faulty Engine Coolant Bypass Valve module/actuator
  • Open/short or damaged wiring between valve and network/ECM
  • Corroded or loose connector pins at valve, harness, or control module
  • CAN/LIN bus fault (missing termination, short to battery/ground, high resistance)
  • Blown fuse or loss of power/ground to the valve module
  • ECM/PCM or gateway module failure or software fault

Symptoms

  • Malfunction Indicator Lamp (MIL) or Service light illuminated
  • Engine coolant temperature control may be incorrect (slow warm-up, overheating, or temperature hunting)
  • Reduced heater performance or auxiliary coolant flow not functioning
  • One or more modules report network communication faults or additional U-codes
  • Possible limp-home mode or drivability restrictions if coolant control is required for emissions control

What to check

  • Read all stored DTCs and freeze-frame/extended data with a full-function scan tool; note time since start and related codes
  • Visually inspect wiring harness and connectors at the Engine Coolant Bypass Valve, ECM/PCM, and gateway module for damage, corrosion, or loose pins
  • Check for related network U-codes (other module communication lost) to identify bus-wide vs single-node issue
  • Verify fuses and relays that supply the valve module and related modules
  • With ignition ON, check for power and ground at the valve connector using a DVOM
  • Use scan tool or oscilloscope to see if the valve module appears on the vehicle bus and whether expected messages are present

Signal parameters

  • CAN bus idle (recessive): CANH ≈ 2.5 V, CANL ≈ 2.5 V (should be close to equal)
  • CAN bus dominant state: CANH rises toward ≈ 3.5 V, CANL falls toward ≈ 1.5 V during messages
  • Expected message frequency: valve/control module transmit interval typically tens to hundreds of ms depending on vehicle (verify with OEM data)
  • Termination resistance: about 60 ohms across CANH and CANL with vehicle power off (two 120 Ω in parallel)
  • Module power: switched or constant 12 V supply present when key ON; ground continuity to chassis

Diagnostic algorithm

  1. Connect a full-function scan tool, read and record U0615 and any related codes and freeze-frame data; clear codes and attempt to reproduce
  2. Check for other U-codes indicating a wider network issue (if present, diagnose bus/termination first)
  3. Visually inspect connectors and wiring at the Engine Coolant Bypass Valve A, ECM/PCM, and intermediate junctions for damage, corrosion, or loose pins; repair as needed
  4. Verify power and ground at the valve connector with ignition ON; repair blown fuses, poor grounds, or power loss
  5. Backprobe the valve module connector while monitoring for CAN activity with a scan tool or oscilloscope; confirm whether the module transmits/receives messages
  6. Measure CANH/CANL voltages and check termination resistance (~60 Ω) across the bus; repair shorts or opens on the bus
  7. If intermittent, perform a wiggle test along the wiring harness while monitoring communications; repair any faulted wiring
  8. If wiring and bus integrity are confirmed but the module does not communicate, attempt to reprogram/update module software per OEM procedure if available
  9. As a last step, substitute a known-good valve module or control unit (or connect the suspect module to a known-good vehicle network if possible) to confirm module failure before replacement
  10. After repairs, clear codes, perform readiness checks and road test to confirm the fault does not return

Likely causes

  • Open or intermittent wiring to valve module
  • Corroded/loose connector at valve or control module
  • Loss of power or ground to the valve module (blown fuse, disconnected pigtail)
  • CAN bus termination problem or short on CANH/CANL
  • Failed valve actuator or its local control module

Fault status

⚠️ Status
Lost communication with Engine Coolant Bypass Valve A module on vehicle network—no valid messages received or data invalid.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours

Similar codes

U0100 U0121 U0140 U0401 U0415
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