What it means
The control module did not wake up cleanly from sleep mode — wake event timing or sequence outside spec.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
A control module leaves sleep mode when it receives a wake event, such as a vehicle input or network message. U3012 sets when the module's wake-up timing or sequence falls outside its expected performance, potentially leaving it unavailable to other modules.
Common causes
Most likely first.
- Module internal fault
- Wake signal noise or glitch
- Gateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules for communication and wake-up codes, and save freeze-frame data to identify the affected module and conditions.
- Check whether the module responds after a normal wake event and whether its status changes consistently in live data.
- Inspect the module's power, ground, wake-signal, and network connectors for loose pins, corrosion, or water intrusion.
- Monitor the wake signal and module supply during wake-up to look for interruptions or electrical noise.
- If the signals are stable, check gateway message routing and assess the module for an internal fault using manufacturer procedures.
Common fixes
- Clean and secure loose or corroded module connectors.
- Repair a damaged or noisy wake-signal wire.
- Correct a confirmed gateway routing issue.
- Repair or replace the control module if its wake-up performance remains faulty with sound power, ground, and signals.
Can I keep driving?
If the affected system operates normally, limit driving to what is necessary until the fault is diagnosed; the module may fail to wake on a later start or vehicle event. Do not drive if the fault disables a safety-related feature or causes limp mode.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.