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VZ V6 faulty ECU testing

lout

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need a little help with a 2005 VZ V6 wagon
has the service vehicle soon, low fuel , loss of communication to ECU
car has been diagnosed as faulty ECU by another mechanic
but i have been asked for a second opinion, it is a workmates wife's car
turning ignition to reds and bypassing crank relay starts engine and brings ecu online
ECU faults can then be cleared
and all is normal for half hour after car is turned off
with start relay reinstalled, car starts like normal
in my mind this cannot be an ECU fault,
what does bypassing start relay do that brings ECU back on line
is it a communication wake up, if so which protocol
is it a current draw
trying to narrow down the diagnosis as time is a bit short this weekend
have checked the grounds which seem fine
will be pulling ECU plugs apart tomorrow and start scoping things out
 

Fu Manchu

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This makes my brain hurt.
 

Fu Manchu

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Sort of similar to what we had with the VZ Exec. It gradually went away. Only way to start was to jump the starter. Then it ran fine.
 

lout

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just got home from work and ran a couple of quick tests
there is always 12v on pin 85 of starter relay which is crank request from ignition switch
according to diagram this comes directly from the ignition switch, so this should only be there when key turned to crank
this voltage is there when car is in fault mode or working mode
edit- found a different diagram that shows pin 85 of start relay is supplied when engine relay is energised ,when ignition is switched to reds, so this is correct
pin 86 of starter relay has 3.5v bias voltage which seems high
now have to wait another half hour for it to fail/go to sleep again
my brain is hurting, i think i must have printed off 50 pages of wiring diagrams, and they dont seem 100% accurate
 
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Fu Manchu

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I posted a video on what you’re looking at. When I get time, I’m happy to sit down and get some brain hurt with you. Won’t be until later though.
 

Fu Manchu

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This is identical to our fault. It wasn’t the ECM as it resolved itself over time. The only thing that happened was the battery health improved. It hadn’t been driven in ages when started.


The relay he uses is the same as VN VP. I have one somewhere. If I can, I’ll get a photo later. Got a bit on.
 

lout

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thanks Fu, i did find your posts when i was researching this, the lady has had a new battery fitted, but as a lot of posts mentioned this car is not driven very often, she has a seasonal business
i have checked all of the relevant inputs and come to the conclusion there is an internal connection that is poor or a weak capacitor. allowing a capacitor to discharge
so the fix is a new ECU
the patch, taking a relay and making a bypass for the ECU starter motor negative output,
(similar to just bridging pin 30 and 87 on start relay), but without triggering all of the fault codes
FYI plug X1 is the bottom and X2 is the upper
relay pin 85 to crank request purple wire X2-31
relay pin 86 to park/neutral input orange/black wire X2-32,
relay pin 87 starter relay neg from ECU yellow wire X2-35
relay pin 30 ground black wire to abs bracket ground
edited due to no park/neutral inhibit, now fixed
when ECU is in fault mode cranks for an extra 2-3 seconds before starting
when ECU in normal mode, been running in last half hour, starts immediately
if you switch to reds when ECU in fault mode and dont start, it will fail system check and bring up the service vehicle soon and fuel gauge error, but will still start when you crank
 
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lout

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hi fu the first video is the exact same scenario
 

lout

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scratch that patch, it enables starter in gear
edited original fix, now safe
can confirm this is working a treat
except for the extended crank 1st start, you would not know any different
 
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Fu Manchu

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Like I said, with use, ours just slowly fixed itself. Had to jump the car less and less.
 
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