What does p0641 code mean on the chevy impala?

The expansion for a P0641 code on the Chevrolet Impala is Sensor Reference Voltage "A" Circuit Open. Was that as clear as mud OK, so what it's saying is that the powertrain control module (PCM) basically supplies a reference voltage to the various onboard sensors (the same way a desktop computer does to its ports) at, say, 5 volts. The sensors verify this voltage signal in reference to whatever measurements they're takeng and send that back to the PCM. So, the message here is that the PCM has detected voltage that's outside of the specification on the 5-volt circuit, and the sensor that triggered this is the number one, or "A" sensor. There aren't any real symptoms here, beyond the check engine light (CEL) illuminating or some gauges that are off; You won't feel the car lurching or entering limp mode, like some other DTCs would entail. Causes here are usually going to be a faulty sensor, a wiring issue (a break/frayed wire is very often the culprit here) or very rarely, a problem with the PCM itself.