01 How to Drive Safely on Slippery Roads: A Comprehensive Guide • 02 The Best Engines That Should Have Been in Sports Cars But W… • 03 Tech Meets Terrain: Xiaomi SU7 Merges Innovation with Adven… • 04 How to tell if your car's engine oil is low or overfilled? • 05 Engineers Created A Paint That Literally Heals Scratches On… • 06 Why Tire Pressure Light Sometimes Comes On Even When Tires … • 07 P0033 Turbo charger bypass valve control circuit • 08 ECU Tuning Explained: Understanding Stages, Benefits, and P… • 09 Electric Vehicles: The Future of Transportation Is Here, an… • 10 Engine Rattles When Accelerating? Diagnose the Cause Yourse… •

DTC codes / U00xx · Network wiring and bus faults / U007E

U007EControl Module Communication Bus L Off

U007E is a generic network communication code indicating that the control module responsible for monitoring the vehicle's communication bus has detected a complete loss of signal on that bus, designated 'L'. The module that set the code can no longer exchange data with other modules on that network segment, which may disable multiple electronic systems at once.

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

Symptoms you may notice

  • Multiple warning lights illuminated simultaneously, including ABS, airbag, traction control, and check engine lights
  • The engine may crank but fail to start, or start and run poorly, because the powertrain control module cannot coordinate with other modules
  • Inoperative accessories such as the radio, climate control, power windows, or instrument cluster
  • A no-start condition where the ignition is on but the starter does not engage or the security system prevents starting
  • Erratic gauge behavior, with the instrument cluster flickering or showing dashes instead of readings
  • Often no symptoms besides the warning light if the failed bus is a secondary network that does not affect drivability

Common causes, most likely first

  1. Open or shorted wiring on the bus L circuit, often from chafing, corrosion, or a broken connector pin
  2. A failed control module that has lost internal power or ground, pulling the entire bus down
  3. Blown fuse or faulty relay supplying power to one or more modules on the bus
  4. Corroded or loose ground connection shared by modules on the network
  5. Water intrusion into a connector or module housing causing corrosion and signal loss
  6. Aftermarket accessory improperly tapped into the bus wiring, creating a short or excessive load
  7. Failed transceiver inside one module that disrupts communication for the entire bus

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes from every module to identify which modules are offline and which bus is affected
  2. Inspect the wiring harness and connectors at each module on bus L for corrosion, chafing, or loose pins, starting at the module that set the code
  3. Check the fuse and relay that supply power to the modules on the affected bus, and verify battery voltage and ground integrity at each module
  4. Measure resistance on the bus L circuit with the battery disconnected to check for opens or shorts, comparing to the manufacturer's specification
  5. Disconnect modules one at a time to see if communication returns, isolating a failed module that is pulling the bus down
  6. Repair or replace damaged wiring, connectors, or the faulty module, then clear codes and verify communication with all modules
  7. Perform a road test and recheck for stored codes to confirm the repair is complete and no intermittent fault remains

What a dead bus L really tells you

  • A single failed module can take down the entire bus L network, so technicians often find the fault by unplugging modules one at a time until communication returns rather than replacing the module that set the code
  • The module that stores U007E is not always the defective one; it is simply the module that noticed the bus went silent, and the actual cause may be a module at the far end of the network
  • Aftermarket alarms, remote starters, and audio equipment tapped into bus wiring are a frequent cause of bus L failure that owners overlook because the installation happened years earlier
  • A weak or failing battery can cause modules to drop offline intermittently and set U007E, so voltage and ground checks must come before any module replacement
  • Bus L is often a low-speed or secondary network, so the vehicle may drive normally with only a warning light, leading owners to postpone repair until multiple systems fail

Can I keep driving with U007E?

Do not drive the vehicle if multiple warning lights are on or the engine will not start, because the failure can disable safety systems and leave you stranded. If the vehicle runs and drives normally with only a warning light, limit driving to a short trip to a repair shop and avoid highways.

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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage