“Since the tachometer pulses on many cars that have this problem with the power circuit to the HEP circuit, most will believe there is a HEP issue especially since the logic board will store a HEP code 54. Since the Power board supplies "8V" to the logic board AND HEP, if this voltage flops around it can cause a HEP signal error which the logic board reports as a code 54. Many turbo Dodge owners reporting HEP issues and swapping the HEP did not solve the problem. Interesting approx 30% of my SMECs have questionable 8V caps but good 5V and 12V caps.”
Miles Snow/chromguy has put together two videos on how to repair the HEP power circuit in the SMEC engine controller.