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DTC codes / U30xx · Network wiring and bus faults / U3007

U3007Control Module Input Power B Circuit/Open

U3007 is a generic body/control module code indicating that a module has detected an open circuit or loss of power on its input power B circuit, which is typically a secondary feed separate from the main battery supply. The computer is not reporting a sensor failure; it is reporting that the voltage on that specific power input has dropped out of range or gone missing entirely.

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

Symptoms you may notice

  • Illumination of the check engine light or a module-specific warning lamp
  • Often no symptoms besides the warning light if the module retains enough power on its main feed
  • Intermittent operation of systems controlled by the affected module, such as lighting, climate, or body functions
  • The module may fail to communicate with a scan tool during diagnostics
  • Random electrical glitches or multiple unrelated codes stored in other modules
  • A no-start or dead accessory condition if the open circuit affects a module critical to starting

Common causes, most likely first

  1. Blown fuse or open fusible link feeding the B circuit of the module
  2. Corroded, loose, or backed-out terminal at the module connector or fuse box
  3. Chafed or broken wire in the harness between the power distribution point and the module
  4. Failed relay that supplies the B circuit, where the circuit is relay-controlled
  5. Water intrusion or rodent damage causing an open in the harness
  6. Internal open circuit inside the module on its power B input pin
  7. Poor ground connection at the module causing the power feed to appear open under load

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module before clearing anything, because U3007 often appears alongside codes that point to the actual circuit
  2. Locate the fuse and relay chart for the affected module and inspect every fuse feeding its power B circuit, replacing any that are open
  3. Perform a voltage drop test on the B circuit at the module connector with the key on, comparing it to battery voltage to confirm the open
  4. Inspect the module connector pins for corrosion, fretting, or push-back, and check the harness for chafing or rodent damage along its routing
  5. Check the module ground circuit with a voltage drop test, since a bad ground can mimic a power open
  6. If the circuit tests good to the module but the code persists, substitute a known-good module or perform a bench test of the power input
  7. Clear codes and verify the repair by cycling the ignition and confirming the module communicates and the code does not return

What the B circuit really feeds

  • The B circuit is usually a keep-alive or secondary power feed, so a failure often leaves the module partly alive and the fault can be missed if you only check the main battery feed at the module.
  • A module that will not communicate at all is a strong clue that the open is on its power or ground rather than a data bus fault, which changes the diagnostic path entirely.
  • Technicians commonly replace a module when the real fault is a pushed-out terminal in the connector that only loses contact when the harness is moved or the vehicle is warm.
  • U3007 can be set by a momentary voltage dip during cranking if the battery is weak, so always load-test the battery and check charging voltage before condemning any wiring.
  • Because this is a generic code, the exact B circuit pin and fuse location vary by make and module, so always consult the specific wiring diagram rather than guessing at the fuse box.

Can I keep driving with U3007?

The vehicle is usually safe to drive if the only symptom is a warning light and all systems operate normally, but avoid long trips or relying on the affected module for safety functions. If the module controls starting, lighting, or stability systems, have it diagnosed before driving further.

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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