I am an engineer in switzerland and I am currently setting up my ECU repair business as a part time job. I have successfull repaired ECUs so far, but one case leaves me stranded a bit.
I am currently working on a PCM0309M for a Mercruiser Optimax engine. The ECU came in as a no com. At the beginning all power supply circuits (5V and 3.3V) were dead. After short investigation I found an open resistor on the main power MOSFET circuit (not burned / just open circuit). After replacing this resistor I have all power supply circuits back alive and the ECU consumes a (in my opinon) healthy amount of current of about 150mA.
Unfortunately this was not the end of the search. I am still not able to communicate with the ECU and also the main power relay does not switch on after ignition power is applied to pin A1. I cannot read ECU with KTag over BDM port and SPI lines to EEPROM seems to be inoperative (voltages ok, but no data transmissions visible). However I do have the 4 MHz signal on the oscillator.
Does anybody now this type of fault? Is there anything else I could check before calling a dead MCU?