Code Definition

P104B — GCU 12V Control Voltage Fail

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Mitsubishi

About P104B

P104B is a manufacturer-specific powertrain diagnostic trouble code recorded for Mitsubishi vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P104B is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

On these Mitsubishi vehicles the Generator Control Unit (GCU) regulates the alternator field, and the Engine Control Module (ECM) monitors the 12V control supply associated with the GCU to confirm proper regulation. DTC P104B sets when, with the engine running, the ECM detects the GCU control voltage deviating outside its acceptable window, typically below 11.5V or above 15.0V, for a sustained period. This indicates a fault in the 12V control circuit between the battery, the ECM, and the GCU, or in the GCU regulation itself. Symptoms can include a charging system warning, a battery that overch...

Join TaT to view the complete code information and diagnostic details.

Quick Facts