anyone know if it is safe to probe wires just before they enter the PCM by inserting a pin to check circuits for continuity/voltage. keeping in mind I dont want to fry my PCM.
IMO, the answer is "it depends". It depends upon which pins are probed.
It also depends on how the pins are probed. For example, if the lead is too big, it could damage the connector. In fact, even with the connector removed, pin damage can result can occur if the test probe is too big. Remember that the dealer uses a "break out box" to perform such tests on a live circuit.
It is also possible to get false results if the battery is still connected. False results are possible depending upon how the Ohm meter's signal is run through the harness.
In many ways it also depends upon the skill/understanding of the person doing the work. For example measuring voltage is safer than measuring resistance. Remember making resistance measurements involves injecting a small current from the meter itself.
The chances of sucess is increased by having accurate and complete wiring diagrams as well as being through and complete in performing the work.
If trying to be absolutely safe, disconnect the battery negative AND disconnect the PCM electrical connector. Ohm through the PCM connector pin to the far end connector pin. Use a scrap piece of wire to return the signal back to the Ohm meter. In this way, the reading will be true and not be affected by the sensors themselves.