2003 Cadillac CTS 03 cts codes CIRCUIT SIGNAL HIGH missfire

The fact that the temp sensors read -40, indicates that you have an open circuit. I have been reviewing the schematic, and it looks loke it would most likely be in the low reference circuit, it seems all the sensors affected share that in common. The low reference, or ground is in the PCM, pin 26 of C1. The fault is simple in terms, the circuit is a bit more complex, as it has a splice where all the low reference wires for the affected sensors come together, splice S111, and these can be hard to locate. The location description is shown as being in the engine harness, approximately 31.5 inches from the bank 2 sensor 1 oxygen sensor, I am assuming it is from the sensor connector. That sensor is on the left(drivers side) of the engine. Do a visual inspection of the harness, looking for possible pinch points, or contact with hot/sharp objects, first. Some other possibilities include a faulty ECM, or connector terminal for this circuit. The ECM connectors on the car are what is called a micro .64, the terminals are very small and can be prone to issues, for example if it is probed with anything other than the proper terminal test tool, it is probably garbage. Terminal 26 of connector C1 at the ECM is the circuit, it is a tan wire, with exception of the low ref circuit of the cam sensor is pink/black up to S111. What I don't understand is the engine hot, fans always on, symptom. The other symptoms would fall right in line with the faults. You can validate the low ref is open by checking continuity to ground with key off, from one of the sensor low ref terminals. The easiest to access would be the MAF sensor, which also incorporates the IAT sensor. Pin 3 is the tan wire that is the low ref circuit, there are three tan wires in this 6 pin connector. Pin 1 is tan, pin 2 is pink, and then pin 3 is tan, hope this describes it for you. I have not mastered posting images on this system yet, and for that I am sorry, I would post you the connector end view of ECM C1. Let me know if you need to pursue this further.