Code Definition

P1221 — Fuel pump second circuit low, or throttle position sensor circuit performance

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

About P1221

P1221 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1221 is stored, the module has detected a signal or supply voltage lower than the expected operating range; a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour; and a sensor-related fault — the reported value from the named sensor is out of spec.

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.

P1221 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

This code carries two different meanings depending on the application, so the first job is always to establish which system the vehicle in front of you actually uses. On applications with a two speed or dual circuit fuel pump arrangement, the Engine Control Module (ECM) drives a second fuel pump circuit to increase delivery under high demand, and DTC P1221 is set when the ECM sees low voltage on that second circuit, meaning it is open, shorted to ground, or the pump is not drawing current when commanded. On applications with an electronic throttle system, the same code number is used for a thr...

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