Generic fault code
U301D — Control module, wake-up circuit A: performance
The control unit stores code U301D when it detects this fault: “Control module, wake-up circuit A: performance”.
Indicative severity: MediumCommunication network
Reviewed by Daniel Morales, founder of Reprorace SL, on
What does code U301D mean?
Control units talk to each other over buses such as CAN. A U code means one control unit has stopped hearing another: the cause may be that other unit, the wiring or the power supply, often a low battery.
- System
- U · Network and communication
- Area
- Communication network · Car system: Electrical system and battery
- Type
- Generic (SAE J2012 / ISO 15031-6): the same meaning on every make
- Indicative severity
- Medium. Diagnose soon: it may raise emissions or consumption, or trigger limp-home mode.
What usually causes code U301D?
- Communication network fault (bus wiring, termination resistor, gateway)
The most likely causes come first. Only a check on the car confirms which one is yours.
What are the symptoms of code U301D?
- Functions of that control module failing or restarting
- Warning lights at start-up or over bumps
- Sometimes the car does not start or the battery runs flat
These are the usual symptoms of this kind of fault: not all of them always appear, and sometimes you notice nothing.
Can I keep driving with code U301D?
With care, and not for long. You can take the car to a workshop, ideally without long trips or heavy loads, and without putting it off: fuel use or emissions may rise and the car may go into limp-home mode (less power). If the light flashes, a red warning light comes on, the temperature rises or you notice a loss of power, noises or smoke, stop as soon as it is safe.
This is guidance only: only someone who checks the car can say whether it is safe to drive.
An indicative description of the code's generic meaning. Each manufacturer may give it a different meaning, conditions or tests: always follow its service information and your workshop's advice.
What you can do yourself
For this kind of fault
Check the battery and that its terminals are clean and tight, and look up that module's fuse in the manual. If the fault appears over bumps or when a cable moves, tell the workshop: it is often a connector or a ground.
Read the code and keep the report: with an ECO-LITE in the OBD socket you see it on your phone or computer, with the data captured when the fault happened.
Look for anything obvious: a loose connector, a disconnected hose, a fuel cap not closed properly or a low fluid level. Do not take apart anything you do not know.
Clear the code only after writing it down or after the repair. Clearing turns the light off, but it also deletes the freeze-frame data and the readiness monitors used at the inspection.
Drive normally for a few days and read the codes again. If the code comes back, the fault is still there: book the workshop and bring the report.
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Related codes
- U301AControl module, wake-up circuit: open circuit
- U301BControl module, wake-up circuit A: signal low
- U301CControl module, wake-up circuit A: signal high
- U301EControl module, wake-up circuit B open
- U301FControl module, wake-up circuit B: signal low
- U3020Control module, wake-up circuit B: signal high
U30xx codes: control module power, ignition and wake-up
In the glossary
Read more: Remote OBD diagnostics: what it is, how it works and what it can't do