U0037 DTC: Vehicle Communication Bus A (-) Shorted to Battery
What Does U0037 Mean?
Diagnostic Trouble Code (DTC) U0037 indicates that the Vehicle Communication Bus A CAN Low (CAN-) circuit is shorted to battery voltage (B+). When CAN Low receives excessive voltage, communication between electronic control modules becomes unstable or stops completely, causing multiple network-related faults.
Symptoms
- Check Engine Light illuminated
- ABS, Airbag, or Stability Control warning lights
- Loss of communication with one or more control modules
- Power windows, mirrors, or door locks may stop working
- HVAC system malfunction
- Instrument cluster warning messages
- Diagnostic scan tool cannot communicate with some modules
- Multiple communication DTCs stored
Common Causes
- CAN Low wire shorted to battery voltage
- Damaged wiring harness
- Worn insulation contacting a B+ circuit
- Water intrusion inside CAN connectors
- Corroded or loose connector terminals
- Faulty control module internally applying battery voltage to the CAN network
- Incorrect aftermarket electrical modifications
Typical Diagnostic Flow
How to Diagnose U0037
- Read all communication DTCs using a professional scan tool.
- Measure CAN Low voltage with a digital multimeter.
- Inspect the wiring harness for contact with battery power circuits.
- Check connectors for corrosion, moisture, or damaged terminals.
- Verify charging system voltage is within specification.
- Disconnect control modules one at a time to isolate the source of the short.
Typical CAN Bus Values
- CAN High: approximately 2.5–3.5 V during normal communication
- CAN Low: approximately 2.5–1.5 V during normal communication
- Network resistance: approximately 60 Ω (Ignition OFF)
- Actual values vary depending on the 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
- U0035
- U0036
- U0038
- U0100
- U0140
Frequently Asked Questions
Can I drive with U0037?
The vehicle may continue to operate, but communication failures can affect safety, body, and convenience systems. Prompt diagnosis and repair are recommended.
What is the most common cause of U0037?
The most common causes are a CAN Low wire contacting a battery voltage source, damaged wiring insulation, water-damaged connectors, or a defective control module.
Will clearing the DTC permanently fix U0037?
No. Clearing the code only removes it temporarily. The DTC will return until the short-to-battery condition on the CAN Low circuit has been repaired.