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DTC codes / U00xx · Network wiring and bus faults / U008D

U008DVehicle Communication Bus G (+) High

U008D is a generic network communication code indicating that the vehicle's main communication bus, often called the CAN bus, has detected an abnormally high voltage on its G (+) signal line. The computer that set this code monitored the bus voltage and found it exceeded the normal high-logic threshold, which can disrupt communication between modules.

SystemNetwork
Code typeGeneric (all makes)
SeverityHigh
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 warning lights on the dashboard, such as ABS, airbag, or traction control, due to lost module communication
  • Intermittent or complete failure of systems like the radio, climate control, or power windows
  • The engine may crank but not start, or the vehicle may fail to start at all
  • Erratic gauge behavior or flickering instrument cluster lights
  • Often no symptoms besides the warning light if the fault is intermittent

Common causes, most likely first

  1. A short to voltage on the CAN G (+) wire, often caused by chafed insulation contacting a power wire
  2. A faulty control module internally shorting the G (+) line to battery voltage
  3. Corroded or damaged connector pins at any module on the bus, creating high resistance or intermittent contact
  4. Damaged or improperly repaired wiring harness, such as after an accident or aftermarket installation
  5. A failed termination resistor inside a module, altering bus voltage levels
  6. Water intrusion into a connector or module, causing corrosion and voltage irregularities

How to diagnose and fix it

  1. Use an OBD-II scan tool to read all stored codes and identify which modules are communicating and which are not
  2. Perform a visual inspection of the CAN bus wiring and connectors for damage, corrosion, or loose pins
  3. Measure the CAN G (+) voltage with a digital multimeter (DMM) at the diagnostic link connector (DLC) with the ignition on, engine off; normal voltage should be around 2.5 to 3.5 volts
  4. Disconnect modules one by one to see if the high voltage disappears, isolating the faulty module
  5. Check for shorts to voltage by measuring resistance between the G (+) wire and battery positive with the ignition off
  6. Repair or replace damaged wiring, connectors, or the faulty module as needed
  7. Clear codes and verify communication is restored by performing a test drive and rechecking for codes

High bus voltage isn't always a module

  • A common oversight is assuming the code points to a failed module, but a simple chafed wire shorting to a 12-volt source can cause the same high-voltage condition.
  • Aftermarket accessories wired incorrectly, such as alarms or audio equipment, often backfeed voltage onto the CAN bus and set this code.
  • The G (+) line is one half of a differential pair; a fault on the G (-) line can sometimes cause the G (+) voltage to appear high, so always check both lines.
  • Some vehicles use multiple CAN buses, and this code may refer to a specific bus; consult the service manual for the exact bus topology before probing.
  • Intermittent high voltage can be caused by a loose battery connection or a failing alternator, so check charging system voltage first.

Can I keep driving with U008D?

If the vehicle starts and drives normally, you may drive it cautiously to a repair shop, but avoid long trips and be prepared for systems to fail unexpectedly. If the engine stalls, multiple warnings appear, or the vehicle fails to start, do not drive and have it towed to prevent safety risks.

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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