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DTC codes / U30xx · Network wiring and bus faults / U301E

U301EControl Module Wake-up Circuit B/Open

U301E indicates that a control module has detected an open circuit on the wake-up line, which is the wire used to signal a module to power up from sleep mode. The module expects a voltage signal on this circuit when the ignition is turned on or when another module requests communication, but it sees no voltage, so it sets this code and may fail to wake up or communicate.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • The warning light for the affected system may illuminate, such as the check engine light or a module-specific warning.
  • The module may not respond to a scan tool, causing communication errors or a 'no communication' message.
  • Electrical accessories or functions controlled by the module may become inoperative, such as power windows, climate control, or lighting.
  • The vehicle may experience a parasitic battery drain if the module remains awake or fails to sleep properly.
  • Often no symptoms besides the warning light, especially if the module is not critical for driving.

Common causes, most likely first

  1. A broken or corroded wire in the wake-up circuit, often due to flexing, chafing, or rodent damage.
  2. A poor connection at a connector, such as loose pins, corrosion, or water intrusion.
  3. A faulty control module that is not providing the wake-up signal or has an internal open circuit.
  4. A blown fuse that supplies power to the wake-up circuit, though this is less common as wake-up circuits are often low-current.
  5. A short to ground or short to voltage on the wake-up line, causing the signal to be lost.
  6. Ignition switch or push-button start failure that does not send the wake-up signal.
  7. A defective relay or power distribution module that routes the wake-up signal.

How to diagnose and fix it

  1. Check all fuses related to the affected module and the wake-up circuit using a test light or multimeter.
  2. Inspect the wake-up circuit wiring for visible damage, corrosion, or loose connectors, especially at the module and any intermediate connectors.
  3. Use a wiring diagram to identify the wake-up circuit and measure voltage at the module connector with the ignition on; compare to specifications.
  4. Perform a continuity test on the wake-up wire from the module to the power source or signal origin to check for opens.
  5. Check for shorts to ground or voltage on the wake-up line using a multimeter and isolate by disconnecting components.
  6. If the circuit tests good, substitute a known-good module or perform a module communication test to confirm module failure.
  7. Repair any damaged wiring, replace faulty connectors, or replace the module as needed, then clear codes and verify the repair.

Wake-up Circuit Diagnostics Beyond the Obvious

  • A wake-up circuit is often a low-current signal wire that can be easily damaged by rodent chewing or chafing, so inspect hidden areas of the harness thoroughly.
  • The code may be set by a module that is not the one you are scanning; always check all modules for communication and look for related codes in other modules.
  • A weak battery or poor ground can cause modules to fail to wake up, so load-test the battery and check ground connections before condemning a module.
  • Some vehicles use a dedicated wake-up wire from the body control module (BCM) to other modules; a failure in the BCM can set this code in multiple modules.
  • After repairing the circuit, some modules require a sleep cycle or battery disconnect to reset the wake-up logic, so do not assume the repair failed if the code persists immediately.

Can I keep driving with U301E?

If the affected module controls safety systems like airbags or stability control, avoid driving until repaired. If it only affects convenience features, you may drive with caution, but monitor for battery drain and ensure critical systems are operational.

Tools that help

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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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