Vz sv6 won't start by key

[Rich00]

Gday all
I have a 05 sv6 auto.
It has developed a ongoing problem and has gotten worse and worse gradually.
If i try to start the engine all that happens is 'fuel gauge error' and 'service vehicle soon'.
The immobilser is not activated and no other lights on dash indicating other issues.
It does have a U0100 code indicating loss of connection to ecm/pcm.
However, if i leave the key on 'on' and remove the starter relay and run a direct wire from the 30 to 87 in the starter relay she fires up and runs mint.
Once running still throws the u0100 code however doesn't seem to effect it as i can turn car off and start with key for upto about 30 min. After that i have to go through the same procedure again.
I have seen a few posts relating to ecu failures resulting in this, would this be the same in my situation? If so is there a cheap way to get around it or repair? Obviously these cars aren't worth much anymore and quite silly to spend upto 1k on a 2k car.
I should add all fuses are a1 and relays have been swapped around to check it wasn't only a relay issue, which has had the exact same outcome
Any help or experience is much appreciated.
Thanks

 

[ForestVt]

After more than 6 months experiencing this problem ... and searching the various similar occurrences reported in this forum, I agreed with the diagnosis that indicates that this fault is the result of very high temperature in the ECU. Thanks to Jason ( akaTazzi - Envyous Customs)

My previous diagnostics included: Ground fault, electrical noise caused by poor relay contact, low battery voltage, ignition key contact failure in the immobilizer system, etc. Finally ... I established a direct relationship between the occurrence of the fault and a very high temperature in the body of the ECU (always above 80 degrees Celsius - always measured with my laser gun thermometer).

I also concluded from web searches ... that the occurrence tends to render the ECU unusable at some point. I myself "opened" the ECU module in my car, after observing photos with "physical" evidence of this type of failure posted on the internet. With the help of a microscope, I deduced that my ECU did not - yet - have the 'mechanical' degradation suggested as resulting from prolonged exposure to the extreme regime of temperatures and vibrations. These are the typical conditions of the GM design position for mounting the ECU on the Alloytec 3.6 VZ (Omega CD here in Brazil).
(screwed firmly in front of the head and behind the radiator)

More than a year ago ... I changed the design of fixing the ECU in my car! (see attached photos) Since then, there have been no further occurrences of the failure. Fortunately ... it was not necessary (in my case) to replace the ECU.

Another significant detail: In this position ... the ECU never reaches temperatures of 80 degrees Celsius or higher - even in the most severe ambient temperature and traffic congestion conditions.

I hope this helps your diagnosis. Or even in the adoption of this homemade solution.
(note of good humor: as far as I know ... this is not an approved solution for use with delegation of responsibilities..kkk)!