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DTC codes / U00xx · Network wiring and bus faults / U0007

U0007High Speed CAN Communication Bus (-) Low

U0007 means the modules on the high-speed CAN (Controller Area Network) data bus have detected that the CAN low signal wire is shorted low or otherwise pulled below its normal voltage range. The computer is not reporting a failed module; it is reporting that the differential bus voltage on the CAN low line has collapsed, which disrupts communication between control units.

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 ABS, traction control, and stability control
  • The engine may still start and run normally because the fault often affects only certain modules
  • Intermittent or complete loss of communication with scan tool for one or more control modules
  • Erratic operation of systems that share the bus, such as the radio, climate control, or instrument cluster
  • Often no symptoms besides the warning light if the short is intermittent or confined to a non-critical segment
  • Transmission may default to limp mode or fail to shift normally on some vehicles

Common causes, most likely first

  1. A chafed or pinched CAN low wire shorting to ground or to a nearby metal component
  2. Water intrusion into a connector or module causing corrosion and a low-resistance path on the CAN low circuit
  3. A failed control module internally shorting the CAN low line to ground
  4. A damaged or improperly installed aftermarket accessory tapping into the bus wiring
  5. A faulty terminating resistor inside a module dragging the bus voltage down
  6. Loose or backed-out terminal in a CAN bus connector creating an intermittent short
  7. Battery or charging system problems causing modules to behave erratically and set bus faults

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module to map which systems are affected and whether U0007 is current or history
  2. Measure resistance between CAN low and ground at the diagnostic link connector with the battery disconnected to check for a hard short
  3. Inspect the CAN low circuit wiring and connectors for chafing, corrosion, water intrusion, and previous repair damage
  4. Disconnect modules one at a time from the bus and recheck the CAN low voltage to isolate an internal module short
  5. Check for aftermarket accessories or alarms spliced into the bus wiring and remove or repair any improper connections
  6. Repair or replace the damaged section of CAN low wiring, then clear codes and verify communication with all modules
  7. Perform a road test and recheck for returning codes to confirm the repair is complete

What U0007 does not always mean

  • A U0007 code does not automatically mean a module has failed; a simple chafed wire behind a kick panel or under the hood is a far more common cause.
  • Many technicians replace a control module only to find the same code returns because the real fault is a corroded connector pin that was disturbed during the repair.
  • Aftermarket remote starters, alarms, and dash cameras spliced into the CAN bus are a frequent and easily overlooked source of a CAN low short.
  • A weak battery or failing alternator can cause multiple modules to set bus communication codes that disappear once charging system voltage is corrected.
  • The CAN low wire can short intermittently only when the vehicle is moving or over bumps, so a static resistance test may pass while the fault is still present.

Can I keep driving with U0007?

If the vehicle starts, runs, and drives normally with only a warning light, you can drive it cautiously to a repair shop, but avoid long trips and towing. If multiple warning lights are on, the transmission is in limp mode, or the engine stalls, stop driving and have the vehicle towed because loss of communication can disable safety systems.

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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