High Speed CAN Communication Bus (+) Low
2010-2021 Fiat Uno 1.0L I4 Flex Fire Evo
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
Fiat 124 Spider
2017-2020 1.4L I4 Turbo
Fiat 126p Maluch
1973-2000 0.65L I2 Air-Cooled
Fiat 126p Maluch
1987-2000 0.7L I2 Air-Cooled
Fiat 500
2012-2019 1.4L I4
Fiat 500 Abarth
2012-2019 1.4L I4 Turbo
Fiat 500 BR
2011-2020 1.4L I4 Flex Fire Evo
Fiat 500 PL
2007-2025 1.0L I3 Hybrid FireFly 70
Fiat 500 PL
2007-2025 1.2L I4 Fire 69
Common Questions
What does code U0004 mean on a 2010-2021 Fiat Uno?
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 Fiat Uno?
Common symptoms of U0004 include: Communication failures, Multiple DTCs from various modules, Intermittent system operation.
What causes U0004 on a 2010-2021 Fiat Uno?
Common causes of U0004 include: CAN H wire shorted to ground, Module pulling CAN H low, Damaged wiring insulation, Water intrusion in connector.