U0038 DTC: Vehicle Communication Bus A Performance
What Does U0038 Mean?
Diagnostic Trouble Code (DTC) U0038 indicates that Vehicle Communication Bus A is operating outside its expected performance range. Unlike an open circuit or short circuit fault, this code means the CAN network is still active but communication is slow, unstable, delayed, or corrupted between one or more electronic control modules.
Symptoms
- Check Engine Light illuminated
- Multiple warning lights on the dashboard
- Intermittent communication with control modules
- Power windows, mirrors, or door locks operate erratically
- HVAC system responds slowly or intermittently
- Instrument cluster communication warnings
- Random communication-related DTCs
- Diagnostic scan tool may lose communication intermittently
Common Causes
- High resistance in the CAN Bus A wiring
- Loose or corroded connectors
- Water intrusion into CAN connectors
- Weak battery or unstable charging system voltage
- Damaged wiring harness
- Faulty CAN transceiver inside a control module
- Failing BCM, PCM, or another network module
- Improper aftermarket electrical accessories
Typical Diagnostic Flow
How to Diagnose U0038
- Read all stored communication DTCs using a professional scan tool.
- Inspect the CAN Bus A wiring for damage or excessive resistance.
- Check connectors for corrosion, moisture, or loose terminals.
- Measure CAN bus resistance (approximately 60 Ω with the ignition OFF).
- Verify CAN High and CAN Low voltages using a digital multimeter.
- Test battery and charging system voltage.
- Disconnect suspected control modules individually to isolate the source of network instability.
Typical CAN Bus Values
- CAN High: approximately 2.5–3.5 V
- CAN Low: approximately 2.5–1.5 V
- Network resistance: approximately 60 Ω (Ignition OFF)
- Actual specifications vary by vehicle manufacturer.
Estimated Repair Cost
- CAN wiring repair: $80–300
- Connector replacement: $30–150
- Professional CAN network diagnosis: $100–250
- Control module replacement: $250–1,000+
Related DTCs
- U0036
- U0037
- U0039
- U0100
- U0140
Frequently Asked Questions
Can I drive with U0038?
Yes, but unstable CAN communication can affect safety systems, body electronics, and vehicle convenience features. The problem should be diagnosed as soon as possible.
What is the most common cause of U0038?
The most common causes are poor CAN wiring connections, high circuit resistance, low battery voltage, corroded connectors, or a failing control module.
Will clearing the DTC permanently fix U0038?
No. Clearing the code only removes it temporarily. If the CAN Bus A performance problem remains, the DTC will return after the next network self-test.