U0636

Code

Generic U — Network/User

Lost Communication With Hybrid/EV Battery Pack Coolant Control Valve A

Brand: Generic

Type: U — Network/User

Views: UK: 37 EN: 48 RU: 30

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty or disconnected connector at coolant control valve/module
Damaged wiring harness (open, short to ground, short to battery, high resistance) between valve and vehicle network
Blown fuse or failed power/ground supply to the valve/module
Failed coolant control valve actuator or local control module
CAN bus wiring fault (open, short, incorrect termination, high impedance)
Corroded terminals or water ingress in connector

Symptoms

Malfunction Indicator Lamp (MIL) or warning light illuminated
Message or DTC related to battery thermal management or coolant control displayed
Battery pack temperature control not responding or operating improperly
Reduced charging/drive performance or limp-home behavior by hybrid/EV system
Battery overtemperature or thermal management warning
Possible audible/visual HVAC or coolant system faults

What to check

Use a capable scan tool to read U0636 and any related freeze-frame and concurrent codes
Confirm whether the coolant valve/module appears on the network (module present list) and whether it responds to requests
Inspect the connector and wiring at the coolant valve/module for corrosion, damage, or moisture
Check fuses/relays supplying power to the valve/module and verify proper ground connections
Perform a wiggle test on the harness while monitoring communication for intermittent faults
Measure CAN bus voltages: CANH ≈ 2.5–3.5 V at idle, CANL ≈ 1.5–1.0 V; verify differential signal and termination resistance (~60 Ω between CANH and CANL)

Signal parameters

Expected network: CAN (high-speed) messages from Battery Pack Coolant Control Valve A or its local controller
Typical idle voltages: CANH ~2.5–3.5 V, CANL ~1.5–1.0 V, differential ~2.0 V
Termination resistance: ~60 Ω between CANH and CANL (two 120 Ω terminators in parallel)
Module should respond to diagnostic session requests and periodic status messages (frequency depends on vehicle; often periodic milliseconds to seconds)
Power supply: typically battery voltage (check +12 V or vehicle nominal supply) at valve/module connector pins
Ground:

Diagnostic algorithm

Read and record U0636 and any additional codes, freeze-frame, and occurrence count. Attempt to clear codes and see if U0636 returns.
Verify whether the battery pack coolant control valve/module is listed and reachable with the scan tool. Note response or lack thereof.
Visually inspect the valve/module connector and harness for damage, corrosion, or moisture. Repair or clean connectors as necessary.
Check fuses and relays that supply power to the valve/module. Verify battery voltage at the power pin and good ground at the ground pin.
Perform basic electrical checks: with ignition on, measure voltage at the module power pin, check for proper ground, and measure resistance/continuity of the control/communication wires to the main control module.
Verify CAN bus integrity: measure CANH and CANL voltages, check termination resistance (~60 Ω), and look for shorts to battery or ground. Use an oscilloscope to inspect for valid CAN waveforms and message traffic if available.
If wiring and power/ground are good but the module does not communicate, attempt to reset or reflash the module per manufacturer procedures (if available) or swap with a known-good module where applicable.
Replace the coolant control valve/module only after verifying harness, power, ground, and network are good. After repair, clear codes and road/test to confirm fault does not return.

Likely causes

Connector corrosion or poor pin contact at coolant valve/module
Broken or chafed wiring in harness near suspension/hinge/engine bay
Blown fuse or poor ground to the valve/module
Failed coolant control valve actuator or its integrated controller

Fault status

⚠️ Status

Lost Communication With Hybrid/EV Battery Pack Coolant Control Valve A — communication messages not received by controller; DTC stored (may be intermittent or continuous).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours