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DTC codes / U00xx · Network wiring and bus faults / U0071

U0071Vehicle Communication Bus E (-) High

U0071 is a generic network communication code indicating that the vehicle's Controller Area Network (CAN) bus E negative circuit is reading a voltage higher than the manufacturer's specified threshold. The computer detected an abnormal high-voltage condition on the CAN E (-) line, which can disrupt data exchange between control modules on that bus segment.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) or a dedicated communication warning light
  • Multiple unrelated warning lights on the dashboard, such as ABS, airbag, or traction control
  • Intermittent or complete failure of modules on bus E to communicate with the scan tool
  • Erratic operation of accessories or systems that share the affected bus segment
  • The engine may run normally with no noticeable performance change
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Damaged or chafed CAN E (-) wire shorted to voltage or to the CAN E (+) wire
  2. Poor electrical connection at a module connector on bus E, such as corrosion or loose pins
  3. Failed control module on bus E internally shorting the negative line high
  4. Water intrusion into a connector or module causing conductive paths
  5. Aftermarket accessory improperly tapped into the CAN E wiring
  6. Faulty termination resistor on the bus segment causing voltage bias issues

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes and freeze-frame data before clearing anything
  2. Inspect the CAN E (-) circuit wiring and connectors for damage, corrosion, or loose pins
  3. Measure voltage on the CAN E (-) line with a digital multimeter and compare to specification
  4. Disconnect modules on bus E one at a time to see if the high voltage condition disappears
  5. Check for aftermarket accessories wired into the CAN E circuit and remove or repair as needed
  6. Repair or replace the faulty wire, connector, or module identified during testing
  7. Clear codes and verify communication on bus E with a scan tool after repair

What most technicians miss on U0071

  • A high voltage on CAN E (-) often points to a short to power rather than a simple open circuit, so check for wires routed near high-current sources.
  • Modules on other buses can set U0071 as a secondary code when a gateway module fails to translate messages correctly.
  • Aftermarket alarms or remote starters tapped into the CAN E wiring are a frequent cause that owners forget to mention.
  • The code can be set by a module that remains powered after key-off due to a stuck relay, keeping the bus voltage biased high.
  • Never assume the module reporting U0071 is the faulty one; the code often originates from a different module on the same bus segment.

Can I keep driving with U0071?

If the vehicle runs and drives normally, you can drive it to a repair shop, but avoid long trips and be prepared for warning lights or accessory malfunctions. If multiple systems fail or the engine stalls, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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