U3007 indicates that a control module is detecting an open circuit in its power supply input B. This means the module is not receiving the expected voltage, typically due to a power or ground fault in the wiring harness rather than an internal computer failure.
The most common cause - the fuse protecting the affected module's power circuit has failed, creating an open circuit.
Physical damage, corrosion, or broken wires in the power circuit between the fuse panel and the control module can create an open condition.
If the module uses a relay for power switching, a failed relay can prevent voltage from reaching the module.
Poor connection at the module connector or fuse panel can create high resistance or open circuits.
The module itself may have an internal power circuit failure - this is less common but possible, especially with age or electrical stress.
The main engine computer is almost never the cause of U3007. It should be investigated last and only after confirming all power/ground/wiring issues are ruled out.
It depends on which module is affected. Safety-critical modules like ABS or transmission control may affect vehicle operation and should be addressed promptly.
Limited driving may be possible depending on which module is affected, but warning lights will be present and certain vehicle functions may be disabled. Have it diagnosed to avoid being stranded.
Almost never. U3007 is a power/ground circuit issue, not a computer issue. The PCM rarely fails and should be the last thing checked after all fuses, wiring, relays, and connections are verified good.
Some technicians may not thoroughly investigate circuit-level issues and default to the most expensive repair. Always verify power, ground, and wiring first - these are the true causes in the vast majority of U3007 cases.