P1260 on a GM vehicle means the body control module (BCM) or theft deterrent module has commanded the powertrain control module (PCM) to immobilize the vehicle because a security test failed or a theft event was detected. The PCM stores this code when it receives the immobilization signal from the vehicle theft deterrent system, often preventing the engine from starting or causing a no-crank condition.
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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