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5v supply error - increasing above 5v


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Hey guys - I've got a strange one.

I'm getting a error 74, but instead of the 5v being loaded down it actually rose to 5.6v first.

Other than the TPS I've got Oil and Fuel pressure sensors running off it.
As the car warmed up you can see the Air and Water temps start to raise as you'd expect.
But then suddenly the 5v increases to 5.6v and it throws out all the sensor readings along with it.
Then strangely I get a sudden low spike on DI2 (AC request) and that resets the 5v supply back to exactly 5v and all the sensors come back in-line.

Moments later the AC request drops low again and triggers the 5v supply to rapidly oscillate between 5v and 0v until the car stalled.

The Link isn't controlling the AC, but I've got the clutch request hooked up so I can control Idle/Fans/etc so have the 12v trigger  wired into DI2.

I havent started pulling the loom apart yet to see if I've got any shorted wires but I'm highly suspicious since DI2 is right next to the 5V pin in the ECU plug.

Unless I'm barking up the wrong tree and when the 5V begins to fail due to a bad pressure sensor for example the digital inputs also become unreliable?


PC Datalog - 2022-12-10 12;24;37 pm.llgx

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Well I guess I wasn't barking up the wrong tree...

Pictured left to right: DI2, 5v Supply and AN3.

DI2 and 5V are black and burnt so they were clearly shorting inside the plug even though there is no evidence of stray wires etc.
Now sure how that would happen. Also when I pulled out AN3 to compare its condition the tip broke off and got stuck inside the connector.

Guess I'm repinning the lot now.

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I would say the "black" has possibly come before the short.  Not sure what it got hot from in the first place, but the short was probably caused by the carbonised plastic that is surrounding those pins.  So I would replace the connector housing also.

The crimping doesnt look good at all.  Get yourself a 1026CT, about the cheapest crimp tool that can do a decent crimp on these terminals, and a very useful tool in general for many efi terminals, well worth the $30 investment.  Note the insulation crimp is meant to be a round cavity not a F crimp like you have there. 


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It's strange that it was just between those two pins. Nothing should have been putting that much current through either of those pins.

But it's the only thing that makes sense for the 5v to actually go above 5v - if it was shorting to 12v from the ac trigger signal.

Then I guess the ECU shut off the 5v to protect it (I hope so anyway) which also shut off the ac trigger signal.

I'll get a new plug and re-pin it one by one - hopefull there arent too many pins I need to redo/replace.

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