What it means
Open circuit on the wake-up signal line A — module cannot be woken from sleep via this path. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
Wake-up circuit A carries a signal used to bring the module out of sleep mode. U301A sets when this circuit is open, so the module may not wake through that path and may fail to communicate when a vehicle function requests it.
Common causes
Most likely first.
- Wake-up wire broken
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
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 and save freeze-frame data to identify which module reports the open wake-up circuit A fault and when it occurred.
- Check whether the affected module responds to other wake events and inspect live data for its wake or sleep status.
- Inspect the wake-up A wire, connector terminals, and relevant fuse or splice for a break, loose pin, corrosion, or water damage.
- Test wake-up A circuit continuity from its source to the module connector with the circuit isolated as specified by the manufacturer.
- If continuity is good, verify that the wake signal reaches the module during a wake request and check gateway routing if the signal is network-controlled.
Common fixes
- Reconnect or clean a loose or corroded wake-up A terminal.
- Repair a broken wake-up A wire or damaged splice.
- Replace a damaged connector terminal in the wake-up A circuit.
- Correct a confirmed gateway routing fault if the circuit wiring and signal are sound.
Can I keep driving?
The module may stay asleep and leave dependent functions unavailable, even if the vehicle currently starts and runs. Avoid driving if the affected function is safety-related or if warnings, limp mode, or shutdown occur.
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.