PCM0309M with a dead MCU?

Hi, my name is Enrico.

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?

Best regards

Enrico

3 comments

3 Comments

Maic Salazar Diagnostics

Aug 16, 2023

•

These modules are very reliable, most of the time when a problem like this shows up, ends with a bad MICRO, try the oscillator, to see if you get communication back.

amannenrico

Aug 20, 2023

Replying to

Hi Maic, thanks for your reply. A new oscillator did not fix the problem. I am going to repalce the MCU next. Hope for the best. Enjoy your sunday!

maicsa2

Please add pictures here so others can see the process. Not sure if on these PCMs, will end up damaging the pads under the MICRO. For those that are not familiar, this board is made of a clear layer and 3 layers for ground, power and signals, all this is glued to an aluminum casing, for heath dissipation.