01 Don't Get Stranded! A Guide to Roll Starting, Starters, and… • 02 The Inner Workings of Automotive Airbags: From Sensors to I… • 03 ECU Remapping: What It Is and How It Can Benefit Your Car • 04 Why Buying A New Model Car In Its First Year Could Be Your … • 05 Your ultimate checklist for buying a used car with confiden… • 06 Is it better to leave a car engine running when changing th… • 07 B0017 and B0018: Right Front or Passenger Frontal Deploymen… • 08 This Is Why Your Car’s Extended Warranty Is A Scam • 09 P0045, P0046, P0047, and P0048: Turbo or Supercharger Boost… • 10 How Automatic Transmissions Decide When to Shift •

DTC codes / U06xx · Network communication / U063A

U063ALost Communication With Hybrid/EV Electronics Coolant Temperature Sensor C

U063A is a network communication fault indicating that a control module has lost the data signal from the hybrid or electric vehicle electronics coolant temperature sensor circuit, typically over the CAN bus. The computer has detected that the expected temperature message from that sensor has stopped arriving within the required time window, not necessarily that the sensor itself has failed.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message, often with no other noticeable symptoms
  • Reduced hybrid system power or a forced limp-home mode if the coolant temperature reading is critical for battery thermal management
  • Electric cooling fans running continuously at full speed as a failsafe default
  • Inaccurate or missing coolant temperature display on the instrument cluster or energy flow monitor
  • Intermittent warning lights that appear and disappear with vibration or moisture
  • Possible charging system or hybrid battery performance warnings if the module substitutes a default temperature value

Common causes, most likely first

  1. Damaged or corroded wiring harness between the coolant temperature sensor and its control module, especially at connectors exposed to heat and vibration
  2. Failed hybrid/EV electronics coolant temperature sensor itself, reading open or shorted internally
  3. Loose or contaminated pins in the sensor connector or the module connector causing intermittent CAN communication
  4. Faulty control module that cannot process or transmit the sensor data, often due to internal communication circuit failure
  5. Low or contaminated hybrid cooling system fluid causing the sensor to read outside expected range and the module to flag the message as missing
  6. CAN bus network fault such as a shorted or open data line that disrupts messages from multiple modules including the temperature sensor
  7. Aftermarket accessories or improper previous repairs that introduced electrical interference or incorrect wiring on the communication circuit

How to diagnose and fix it

  1. Connect a scan tool and record all stored and pending codes in every module, then verify the live coolant temperature data from the hybrid/EV electronics sensor to confirm the signal is truly missing or erratic
  2. Visually inspect the sensor, its connector, and the wiring harness for chafing, corrosion, heat damage, or loose pins, and perform a wiggle test while watching live data
  3. Check the hybrid cooling system fluid level and condition, and verify the sensor is properly seated and not coated with debris or sealant
  4. Measure resistance across the sensor at known temperatures and compare to the manufacturer's specification to rule out a failed sensor
  5. Backprobe the sensor signal and ground circuits at the module connector to check for continuity, short to ground, or short to voltage, repairing any damaged wire or connector
  6. If wiring and sensor test good, substitute a known-good sensor or module only after confirming power and ground at the module, then clear codes and road test to verify communication returns
  7. Perform a full CAN bus integrity check with an oscilloscope or breakout box if multiple communication codes are present, and repair any network fault before replacing modules

What the code does not always mean

  • U063A often sets because the control module that publishes the coolant temperature message has lost power or ground, not because the sensor itself has failed, so always check module power and ground before condemning the sensor.
  • A weak or failing 12-volt battery can cause multiple U-codes including this one, because low voltage disrupts CAN bus message timing and makes modules drop off the network intermittently.
  • The sensor may be shared with the cabin heater or battery thermal management logic, so a code for lost communication can appear after a coolant flush or repair where the connector was left loose or the system was not properly bled.
  • Aftermarket remote starters, alarm systems, or phone chargers plugged into the diagnostic port can introduce electrical noise that corrupts CAN messages and triggers communication codes without any hard fault.
  • Clearing the code without checking freeze-frame data often leads to a comeback, because the fault may be intermittent and only appear under specific temperature or vibration conditions recorded in the freeze frame.

Can I keep driving with U063A?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration, long trips, or extreme temperatures because the hybrid system may default to reduced power or inadequate battery cooling. If the vehicle enters limp mode or shows multiple warning lights, stop driving and have it towed to prevent overheating of hybrid components.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage