U0615

Code

Generic U — Network/User

Lost Communication With Engine Coolant Bypass Valve A

Brand: Generic

Type: U — Network/User

Views: UK: 24 EN: 84 RU: 44

AI status

Completed

ready

Completed 100%

Page language: EN

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

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

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

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

Connect a full-function scan tool, read and record U0615 and any related codes and freeze-frame data; clear codes and attempt to reproduce
Check for other U-codes indicating a wider network issue (if present, diagnose bus/termination first)
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
Verify power and ground at the valve connector with ignition ON; repair blown fuses, poor grounds, or power loss
Backprobe the valve module connector while monitoring for CAN activity with a scan tool or oscilloscope; confirm whether the module transmits/receives messages
Measure CANH/CANL voltages and check termination resistance (~60 Ω) across the bus; repair shorts or opens on the bus
If intermittent, perform a wiggle test along the wiring harness while monitoring communications; repair any faulted wiring
If wiring and bus integrity are confirmed but the module does not communicate, attempt to reprogram/update module software per OEM procedure if available
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
After repairs, clear codes, perform readiness checks and road test to confirm the fault does not return