U301F code meaning
Control Module Wake-up Circuit B Low
What U301F means
U301F reports wake-up line B held below its valid level, most often by a short to ground. Since B is a second, independent wake path, the module can still be roused through line A or the network; what it loses is the wake source wired to B. With an edge-triggered input such as the WAKE pin of NXP's TJA1043, which only reacts to a level change that remains stable for a short filter time, a grounded line simply never delivers that change. Its threshold sits only a few volts under battery voltage, so a partly shorted or corroded wire can count as low as well. No manufacturer documents U301F publicly. Unlike U301E, the circuit is not open, so a resistance check to ground with both connectors unplugged is the quickest way to find the fault.
U301F at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U301F
- Function tied to wake source B unavailable
- No other complaint while the module is awake
Common causes of U301F
- Most likelyWake-up wire B chafed and touching ground
- PossibleMoisture or corrosion pulling line B down
- Less likelySource on line B with its output stuck low
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Wakeup circuit bWakeup wiring
What each part of U301F means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 1F | The exact fault in that area. |
What to do next
- Note U301F and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U301F
What does U301F mean?
U301F means "Control Module Wake-up Circuit B Low". U301F reports wake-up line B held below its valid level, most often by a short to ground. It is a generic code, so it means the same on every make.
Is it safe to drive with U301F?
U301F does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U301F fail an emissions test?
U301F is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U301F to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U301F clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.