High Speed CAN Communication Bus (+) Low
2000-2002 Rolls-Royce Corniche 6.75L V8 🇬🇧
Description
The CAN High wire voltage is lower than expected, indicating a short to ground or excessive load on the bus.
Symptoms
- Communication failures
- Multiple DTCs from various modules
- Intermittent system operation
Common Causes
- CAN H wire shorted to ground
- Module pulling CAN H low
- Damaged wiring insulation
- Water intrusion in connector
Diagnostic Steps
- Measure CAN H voltage
- Disconnect modules one at a time to find short source
- Inspect wiring for chafing against ground
- Check connectors for moisture
Repair Notes
Find and repair the short to ground on the CAN H wire. Inspect for damaged insulation.
Related Codes
Other Network Codes
- U0001High Speed CAN Communication Bus
- U0002High Speed CAN Communication Bus Performance
- U0003High Speed CAN Communication Bus (+) Open
- U0005High Speed CAN Communication Bus (+) High
- U0006High Speed CAN Communication Bus (-) Open
- U0007High Speed CAN Communication Bus (-) Low
- U0008High Speed CAN Communication Bus (-) High
- U0009High Speed CAN Communication Bus Shorted Together
- U0010Medium Speed CAN Communication Bus
- U0028Vehicle Communication Bus A Performance
U0004 on Other Vehicles
Rolls-Royce Cullinan
2019-2024 6.75L V12 Twin Turbo
Rolls-Royce Dawn
2016-2024 6.6L V12 Twin Turbo
Rolls-Royce Ghost
2010-2024 6.6L V12 Twin Turbo
Rolls-Royce Phantom VII
2003-2017 6.75L V12
Rolls-Royce Phantom VIII
2018-2024 6.75L V12 Twin Turbo
Rolls-Royce Silver Seraph
1998-2002 5.4L V12
Rolls-Royce Silver Spirit
1990-1998 6.75L V8
Rolls-Royce Silver Spur
1990-1998 6.75L V8
Common Questions
What does code U0004 mean on a 2000-2002 Rolls-Royce Corniche?
U0004 stands for "High Speed CAN Communication Bus (+) Low". The CAN High wire voltage is lower than expected, indicating a short to ground or excessive load on the bus.
What are the symptoms of U0004 on a Rolls-Royce Corniche?
Common symptoms of U0004 include: Communication failures, Multiple DTCs from various modules, Intermittent system operation.
What causes U0004 on a 2000-2002 Rolls-Royce Corniche?
Common causes of U0004 include: CAN H wire shorted to ground, Module pulling CAN H low, Damaged wiring insulation, Water intrusion in connector.