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DTC codes / U00xx · Network wiring and bus faults / U008E

U008EVehicle Communication Bus G (-) Open

U008E means the vehicle's communication network has lost the negative side of one of its data buses, so modules that share that bus can no longer exchange messages reliably. The computer detects an open circuit on the bus-low wire, which is the return path for the differential signal, and it logs the fault when the expected voltage or message traffic disappears.

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

Symptoms you may notice

  • Multiple warning lights on the dashboard, often including the check engine light, ABS, and airbag lamps
  • The engine may start and run, but some electrical features such as power windows or radio controls stop working
  • Intermittent or complete failure of communication with scan tools, preventing some modules from being read
  • Erratic operation of dashboard gauges or the information display
  • Often no symptoms besides the warning light if the affected bus is not critical for driving
  • The vehicle may enter a limp-home mode or refuse to start if the bus carries critical powertrain messages

Common causes, most likely first

  1. A broken or corroded wire in the bus-low circuit, often at a connector or where the harness flexes
  2. A loose or damaged terminal in a communication bus connector
  3. Water intrusion into a connector or module causing corrosion on the bus-low pin
  4. A failed module that internally shorts the bus-low line to ground or power
  5. Aftermarket accessories or poor previous repairs that cut or splice the bus wiring incorrectly
  6. A faulty termination resistor inside one of the modules on the bus, though this is less common
  7. Physical damage to the harness from rodents, road debris, or improper routing

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module to identify which bus is affected and which modules are offline
  2. Obtain the vehicle-specific wiring diagram and locate the bus-low wire, its connectors, and the modules that share that bus
  3. Visually inspect the harness and connectors along the bus-low circuit for chafing, corrosion, water intrusion, or loose pins
  4. Measure resistance from the bus-low pin at the data link connector to the same pin at each module, looking for an open circuit or excessive resistance
  5. With the bus powered down, check for shorts to ground or power on the bus-low wire using a multimeter
  6. Disconnect modules one at a time to see if the bus-low voltage returns to normal, isolating a faulty module
  7. Repair or replace the damaged wire, terminal, or module, then clear codes and verify that all modules communicate and the code does not return

What a bus-low open really tells you

  • A U008E is often set by a poor connection at a single connector rather than a failed module, so a thorough pin-fit and corrosion check saves unnecessary part swapping.
  • The code does not always mean the bus is dead; it can be stored intermittently when the bus-low wire momentarily opens over bumps or during temperature changes.
  • Aftermarket alarms, remote starters, or phone kits tapped into the bus wiring are a frequent cause that many technicians overlook during diagnosis.
  • Some vehicles will set this code when the battery is weak or during jump-starting because low voltage can disrupt bus communication and mimic an open circuit.
  • A module that is completely offline may still be powered and communicating on a different bus, so always check all network segments before condemning a component.

Can I keep driving with U008E?

If the vehicle starts, runs, and has no obvious safety-system warnings, you can drive it to a repair shop, but avoid long trips and be prepared for the engine to stall or systems to drop out. If the engine will not start or multiple safety systems are disabled, do not drive 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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