What Does U0035 Mean?
The CAN-L (negative) line voltage is reading higher than specification, disrupting the differential voltage balance required for CAN communication. This causes communication errors or complete network failure.
Safety Warning
Loss of critical safety systems including airbags, ABS, and traction control. Vehicle is unsafe to operate until repaired.
Common Causes
40%
Short to voltage on CAN-L wire from harness damage or incorrect repair
30%
Faulty control module with failed CAN transceiver driving CAN-L high
15%
Missing or failed terminating resistor causing improper voltage bias
10%
Aftermarket device improperly connected to CAN network
5%
Connector damage causing short between CAN-L and power source
Diagnostic Steps
1
Step 1: Measure CAN-L voltage with ignition on (should be approximately 2.5V, not significantly higher than CAN-H)
2
Step 2: Check for short to power by measuring voltage on CAN-L with ignition off (should be 0V)
3
Step 3: Disconnect control modules one at a time while monitoring CAN-L voltage to isolate faulty module
4
Step 4: Inspect for aftermarket installations and verify proper isolation from CAN network or correct installation
5
Step 5: Check terminating resistor values at both ends of network (each should measure 120 ohms)
Estimated Repair Cost
$150 - $1,000
Parts + labor, varies by vehicle and location
The CAN-L (negative) line voltage is reading higher than specification, disrupting the differential voltage balance required for CAN communication. This causes communication errors or complete network failure.
The most common cause of U0035 (Vehicle Communication Bus A (-) High) is: Short to voltage on CAN-L wire from harness damage or incorrect repair
Typical repair costs for U0035 range from $150 to $1,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of critical safety systems including airbags, ABS, and traction control. Vehicle is unsafe to operate until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0035 to identify the root cause.
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Quick Info
Category
Network
System
Vehicle Communication Network
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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