My 1997 cadillac sls 4.6L northstar has been overheating. I've replaced the t-stat, fan relays, flushed the system and refilled with the sealant pellets as required, and changed the ECT. Also as an HVAC service tech I've tested every circuit of the cooling system. Both fans are not coming on all the time when the a/c is running. Which leads me to believe a possible PCM problem. Such as not completing the circuit to make both fans run. They do run if the a/c is set to come on when the engine is first started, but when you turn the a/c off then back on only the driver's side fan runs. HELP! This is driving me crazy.