U0028moderate severityNetwork
Vehicle Communication Bus A Performance
on 2009 Kia Optima 2.7L V6 · FWD
What this code means
CAN bus A is communicating but performance is below acceptable threshold. Data is being lost or corrupted.
Symptoms
- Intermittent warning lights
- Occasional system glitches
- Delayed module responses
- Scan tool slow or intermittent
Common causes
- High bus load from chatty module
- Degraded wiring causing retransmissions
- Poor termination
- Electromagnetic interference from aftermarket equipment
Diagnostic steps
- Monitor CAN bus load percentage
- Check bus termination resistance
- Scope bus signals for noise
- Remove aftermarket devices and retest
- Check for proper wire twist rate on CAN pair
Repair notes
Reduce bus load or repair wiring quality issues. Ensure proper bus termination.
Other Network codes on this vehicle
U0001
High Speed CAN Communication Bus
U0002
High Speed CAN Communication Bus Performance
U0003
High Speed CAN Communication Bus (+) Open
U0004
High Speed CAN Communication Bus (+) Low
U0005
High Speed CAN Communication Bus (+) High
U0006
High Speed CAN Communication Bus (-) Open
U0007
High Speed CAN Communication Bus (-) Low
U0008
High Speed CAN Communication Bus (-) High
U0009
High Speed CAN Communication Bus Shorted Together
U0010
Medium Speed CAN Communication Bus