U101B: Network Communication Fault (manufacturer-specific)
Severity: medium
What it means: A manufacturer-specific network (U) code. It means one of the car's computers reported a communication or data problem with another module. What it points to depends on the make, so read the description your scan tool shows for your car.
Safe to drive? Depends on the module involved. On a Jaguar XF where it shows up with a gear selector fault, don't drive if you can't reliably select gears.
Common symptoms
- Warning messages on the dash
- Gear selector or transmission warnings (on some Jaguars)
- Other U codes stored at the same time
Likely causes, ranked
- Weak battery or low voltageDIY
- Wiring or connector fault on the networkShop
- A failing module (for example, the gear selector module)Shop
Vehicle-specific notes
- 2009–2015 Jaguar XF: On Jaguar Forums, an XF owner whose rotary gear selector wouldn't rise said U101B and P0850 were stored, and that the problem came and went. Read the full answer · Source
What it means: A manufacturer-specific network (U) code. It means one of the car's computers reported a communication or data problem with another module. What it points to depends on the make, so read the description your scan tool shows for your car.
Severity: Medium. Safe to drive? Depends on the module involved. On a Jaguar XF where it shows up with a gear selector fault, don't drive if you can't reliably select gears.
DIY or shop?
DIY for a battery test; shop for a full network scan with a make-specific tool.
Before you replace parts
- Read all stored codes and freeze-frame data, not just this one.
- Check your VIN for recalls, service bulletins and extended coverage.
- Inspect wiring and connectors for the related sensor or part before buying parts.
- Clear the code only after a repair, then confirm it stays off.
Safety / mechanic note
Verify with a mechanic. Network faults can affect shifting on some cars. A code points to a circuit or system, not always a specific part.