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P1218 on GM vehicles indicates that the powertrain control module (PCM) has detected a fault in the injection pump calibration circuit, which is the electrical path that allows the PCM to read the pump's calibration resistor or feedback signal. The PCM uses this calibration data to precisely control fuel delivery, so when the signal is out of range or missing, the module sets this code and may default to a limp-home fuel strategy.
Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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