U063C

Code

Generic U — Network/User

Lost Communication With Coolant Bypass Valve Actuator B

Brand: Generic

Type: U — Network/User

Views: UK: 24 EN: 40 RU: 32

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, shorted, or damaged wiring between actuator and network/module
Poor or corroded connector pins at actuator or harness connector
Faulty coolant bypass valve actuator or its internal controller
Blown fuse or loss of switched/unswitched power or ground to the actuator
CAN/LIN bus wiring fault, high electrical noise or shorts to battery/ground
Failed or sleeping gateway/module that forwards messages

Symptoms

DTC U063C stored in control module memory; MIL may be illuminated
Engine temperature regulation issues (slow warm up, engine running hot/cold)
Reduced heater/defroster performance or HVAC irregularities
Possible limp-home behavior or reduced engine performance depending on strategy
Actuator does not respond to manual commands from a scan tool

What to check

Read and record all stored codes and freeze frame data from all modules
Check whether the actuator module appears on the network with a scan tool (module present/online)
Visually inspect actuator connector and harness for corrosion, bent pins, or damage
Check fuses and relays for actuator power circuits
Measure power and ground at the actuator connector with key ON
Use a diagnostic tool or scope to verify network messages and bus voltages

Signal parameters

Expected periodic status message from the actuator (alive message) containing position and status bytes
Command vs feedback values: commanded position from PCM/gateway and actuator reported position
Message frequency: periodic heartbeat (typically 1–10 Hz depending on system)
Bus physical layer: CAN differential signaling (idle levels around nominal midpoint; dominant/recessive transitions) or LIN single-wire signaling (depending on vehicle)
Power supply: switched/unswitched battery voltage to actuator and stable ground reference

Diagnostic algorithm

Retrieve all relevant codes and module info. Note occurrence conditions and freeze frame.
Verify whether the actuator module is present on the bus using a factory-level scan tool. If module is absent, continue diagnostics on wiring/power/ground.
Visually inspect connectors and harness for damage, corrosion, or loose pins at the actuator and at any junctions.
With key ON, measure battery voltage at the actuator power terminal and check for a good ground. Repair any open/poor circuits.
Using a scan tool, attempt to command the actuator and observe for response. If no response, check communications with an oscilloscope or CAN/LIN diagnostic tool to confirm presence/absence of messages and proper bus signaling.
Perform continuity/resistance checks of the communication wires and power/ground circuits back to the appropriate control module or junction. Repair any shorts or opens.
Isolate the actuator module (disconnect it) and observe the bus to see if communication to other modules returns to normal or other network errors clear — this can indicate a shorted node.
If wiring and power/ground check good and the actuator still does not communicate, consider replacing or bench-testing the actuator module. If multiple modules show communication faults, investigate gateway/module or termination resistors.
After repair, clear codes, perform relearn or calibration procedures if required, then road-test to confirm the fault does not return.

Likely causes

Connector corrosion or loose pin at the actuator
Damaged wiring harness (chafing, rodent damage) between actuator and module
Actuator internal electronics failure
Intermittent power/ground to the actuator
Faulted network termination or another module pulling the bus dominant

Fault status

⚠️ Status

Lost communication with Coolant Bypass Valve Actuator B — expected status/heartbeat messages not received or invalid. May result in improper coolant bypass control and temperature regulation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours