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DTC codes / U06xx · Network communication / U063E

U063ELost Communication With Exhaust Heat Exchanger Bypass Valve Actuator A

U063E is a generic network communication code indicating that a control module on the vehicle's Controller Area Network (CAN) bus has lost contact with the exhaust heat exchanger bypass valve actuator A. The computer detected that expected periodic messages from this actuator stopped arriving within a defined timeout window, which prevents the module from confirming the bypass valve's position and can affect exhaust temperature management and cabin heating performance.

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

Symptoms you may notice

  • Illumination of the check engine light or a dedicated service warning for the exhaust system
  • Often no symptoms besides the warning light, especially if the bypass valve defaults to a safe position
  • Reduced or inconsistent cabin heating performance, particularly in cold weather
  • A noticeable drop in fuel economy if the exhaust heat exchanger remains in bypass mode
  • Intermittent operation of the bypass valve, sometimes accompanied by other communication-related codes
  • Possible derate or reduced engine power in vehicles that use exhaust heat recovery for emissions control

Common causes, most likely first

  1. Damaged, corroded, or disconnected wiring or connector at the bypass valve actuator
  2. Failed exhaust heat exchanger bypass valve actuator motor or internal electronics
  3. Blown fuse or poor ground connection supplying power to the actuator
  4. CAN bus wiring fault such as an open, short, or excessive resistance on the communication lines
  5. Failed control module that is responsible for communicating with the actuator
  6. Software or calibration issue in the control module causing it to stop polling the actuator
  7. Aftermarket accessories or poor previous repairs introducing electrical interference on the CAN bus

How to diagnose and fix it

  1. Perform a visual inspection of the actuator connector and wiring for corrosion, chafing, or loose pins
  2. Check the fuse and ground circuits that supply power to the bypass valve actuator
  3. Use a scan tool to verify live data and confirm whether the actuator is completely offline or intermittent
  4. Measure CAN bus voltage and resistance at the actuator connector to rule out wiring faults
  5. Substitute a known-good actuator or perform a bidirectional test if the scan tool supports it
  6. Inspect the control module connectors and grounds for signs of water intrusion or loose terminals
  7. If all wiring and power checks pass, replace the actuator and clear the code to verify the repair

What the bypass valve code hides

  • A failed bypass valve actuator often defaults to the open position, so the driver may never notice a problem beyond the warning light.
  • Technicians frequently replace the actuator only to find the real fault is a chafed CAN wire behind the engine block or near the exhaust, where heat damage is common.
  • This code can be set by a low battery or charging system issue that causes momentary voltage drops, so always check battery health before condemning the actuator.
  • Some vehicles use the same actuator for both exhaust heat recovery and cabin heating, so a communication fault can cause poor heater performance that is misdiagnosed as a thermostat problem.
  • The code does not always mean the actuator is dead; a loose ground strap on the engine or transmission can interrupt communication intermittently.

Can I keep driving with U063E?

You can usually continue driving with this code because the bypass valve typically fails to a safe position, but avoid long trips in cold weather if cabin heat is affected and do not ignore repeated warning lights. Have the fault diagnosed promptly to prevent secondary emissions or heating system issues.

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.

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