Shorted or chafed wake-up circuit wiring holding the line at battery voltage; Faulty control module internally shorting the wake-up circuit high; Corrosion or water intrusion in a connector on the wake-up circuit; A module on the network failing to go to sleep and back-feeding the wake-up line; Poor ground connection causing reference voltage shifts on the wake-up circuit; Aftermarket accessory improperly tied into the wake-up or ignition circuit

DTC codes / U30xx · Network wiring and bus faults / U301C

U301CControl Module Wake-up Circuit A High

Q: What does code U301C mean?

Control Module Wake-up Circuit A High. U301C indicates that a control module responsible for waking up other modules on the vehicle's communication network has detected an abnormally high voltage on its wake-up circuit. The module monitors the wake-up line and sets this code when the signal stays above the expected threshold for longer than calibrated, which can prevent proper sleep and wake cycles across the network.

U301C indicates that a control module responsible for waking up other modules on the vehicle's communication network has detected an abnormally high voltage on its wake-up circuit. The module monitors the wake-up line and sets this code when the signal stays above the expected threshold for longer than calibrated, which can prevent proper sleep and wake cycles across the network.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Often no symptoms besides the warning light, especially if the fault is intermittent
Battery drain when the vehicle sits because modules fail to enter sleep mode
Intermittent no-start or delayed start due to modules not waking correctly
Multiple unrelated warning lights or communication codes appearing together
Accessories or modules staying active after the ignition is turned off

Common causes, most likely first

Shorted or chafed wake-up circuit wiring holding the line at battery voltage
Faulty control module internally shorting the wake-up circuit high
Corrosion or water intrusion in a connector on the wake-up circuit
A module on the network failing to go to sleep and back-feeding the wake-up line
Poor ground connection causing reference voltage shifts on the wake-up circuit
Aftermarket accessory improperly tied into the wake-up or ignition circuit

How to diagnose and fix it

Perform a full scan of all modules and record every stored and pending code before clearing anything
Check the battery state of charge and test for parasitic draw with a clamp meter after modules should have slept
Inspect the wake-up circuit wiring and connectors for chafing, corrosion, and water intrusion
Measure voltage on the wake-up circuit at the affected module with the key off and compare to specification
Disconnect suspect modules one at a time to see if the high voltage on the wake-up line disappears
Verify grounds and power feeds to the module that set the code before condemning it
Repair wiring or replace the confirmed faulty module, then clear codes and verify sleep and wake operation

Wake-up circuit faults that mimic module failures

A module that stays awake and back-feeds the wake-up line is a common cause that gets misdiagnosed as a failed module setting the code.
Aftermarket alarms, remote starters, and dash cameras tapped into ignition or wake-up wiring frequently hold the circuit high and set this code.
The code can be set by a low battery or charging system issue that causes reference voltage shifts, so always verify battery health first.
Water intrusion in a connector can create a partial short that only shows up in damp weather, making the fault intermittent and hard to reproduce.
Clearing the code without checking parasitic draw often leads to a repeat visit because the underlying sleep failure remains.

Can I keep driving with U301C?

The vehicle is generally safe to drive, but a persistent wake-up circuit fault can drain the battery and leave you stranded, so avoid leaving it parked for long periods until repaired. If multiple warning lights or a no-start condition appear, have it diagnosed promptly.

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.