U301C: Control Module Wake-up Circuit A High

What it means

Wake-up signal A voltage above expected range — short to power. 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 signals a control module to become active. The module monitors the line and sets U301C when its voltage rises above the expected range, consistent with a short to power. The resulting failure to wake or communicate can disable functions that rely on that module's data.

Common causes

Most likely first.

1. Wiring shorted to battery
2. Gateway module routing CAN messages incorrectly
3. 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

1. Save freeze-frame data and scan all modules for communication faults to find the affected module and see when the high signal occurred.
2. Check live data for wake-up circuit A status or voltage, if available, and compare it with the ignition state.
3. Inspect circuit A wiring and connectors for damage or contact with a powered wire, especially where harnesses pass near ignition or battery feeds.
4. With the circuit isolated as directed by the manufacturer, test for a short from wake-up circuit A to battery or another power feed.
5. If the circuit wiring passes, check gateway routing and CAN network condition, including termination resistance, against the manufacturer's specification.

Common fixes

• Repair wiring that shorts wake-up circuit A to a power feed.
• Repair damaged connectors or terminals that bridge the circuit to power.
• Correct gateway routing or configuration if evidence points to the gateway.
• Repair the CAN network or replace an out-of-spec terminating resistor after confirming the fault.

Can I keep driving?

Limit driving if the affected module controls a needed vehicle function, since it may fail to communicate or dependent systems may enter limp mode. Stop if a safety-related function is affected.