Code Definition

P04C1 — Fuel Fill Door Unlock Control Circuit Low

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Subaru

About P04C1

P04C1 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Subaru vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P04C1 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

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.

Because P04C1 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The powertrain control module (PCM) drives the fuel fill door unlock actuator to release the filler flap and monitors the voltage on the unlock control circuit to confirm the action. During normal operation the PCM expects the control circuit voltage to stay within a specified range, typically around 8V to 14V, for a minimum dwell time while the actuator is energised. DTC P04C1 sets when the PCM detects the circuit voltage remaining below the low threshold limit, indicating insufficient voltage to drive or complete the unlock action, for longer than its built in timeout. This usually points to...

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