U301FControl Module Wake-up Circuit B Low
- Generic OBD-II code · Network
- How the car detects it
- 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.
- What you may notice
- Function tied to wake source B unavailable
- No other complaint while the module is awake
- Likely causes
- LikelyWake-up wire B chafed and touching ground
- PossibleMoisture or corrosion pulling line B down
- RareSource on line B with its output stuck low
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.