What it means
Open circuit on input power line B of the control module (second supply rail, e.g. permanent +12V vs switched battery feed).
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
A control module uses input power B as one of its supply feeds, separate from its other power input. The module sets U3007 when it detects that this B feed is open, so it may lose power or behave unpredictably even if another supply remains available.
Common causes
Most likely first.
- Supply fuse blown
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and save freeze-frame or event data first to see which module reports U3007 and whether related supply or communication codes are present.
- Check the fuse supplying that module’s input power B and inspect for a blown fuse or signs of a short that could have caused it to fail.
- With power off as directed by the manufacturer, inspect the module’s input power B wiring and connectors for looseness, corrosion, damage, or an open conductor.
- Compare voltage at the module’s B power pin with the manufacturer’s specification in the relevant ignition states, and check whether the feed remains present under load.
- If the power B feed tests correctly, check whether other modules also report communication faults and investigate gateway routing or CAN network faults using the manufacturer’s diagnostic procedure.
Common fixes
- Replace the blown input power B fuse after finding and correcting the cause.
- Repair a loose, corroded, or damaged input power B connector or wire.
- Repair the gateway or CAN network fault if testing confirms messages are being routed incorrectly.
- Replace or repair the CAN terminating resistor if testing shows it is outside the manufacturer’s specification.
Can I keep driving?
Avoid driving if the affected module controls steering, braking, restraints, or other essential functions, or if the vehicle shuts down or enters limp mode. A lost supply can disable functions or cause further module communication faults.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.