U3506 means a control module has detected an abnormally high voltage on its dedicated 'Input Power B' supply circuit—often a battery or ignition feed. The module compares the circuit voltage to an internal reference, and when the reading stays above the calibrated threshold, it stores this code. It does not necessarily mean the module itself has failed; the high reading usually originates in the vehicle’s charging system, wiring, or grounds.
A faulty voltage regulator or alternator can push system voltage above normal, raising all module supply circuits and causing a high-voltage reading.
The feed wire may be pinched, chafed, or melted and touching a higher-voltage source, pulling the module’s input above its expected range.
A corroded, loose, or overloaded ground can raise the module’s local reference voltage, making a normal supply appear high relative to module ground.
Corroded terminals, damaged splices, or a failing relay or fuse panel can create voltage anomalies on the circuit feeding the module.
If charging voltage and all wiring/grounds are verified normal, the module’s internal voltage-sensing circuitry may be faulty and misreporting the circuit as high.
Usually not. Most instances are caused by high charging voltage, a short to voltage in the power feed circuit, or a ground problem. Replacing the module before checking the circuit is a common misdiagnosis.
It is not advisable for long. Sustained high voltage can damage the module, bulbs, and other electronics, so diagnose it promptly.
Yes. An alternator or regulator that overcharges the battery can raise system voltage enough to trigger this code in one or more modules.
A scan tool to read codes and data, a digital multimeter for voltage and ground measurements, and the wiring diagram for the affected module are usually sufficient.