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ran power wire now i got error lights


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KPierson 
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Posted: June 01, 2012 at 10:30 AM / IP Logged  
There are separate 5v feeds for each sensor so you can cut the wire with no issues. This is why I assume there is one internal power supply with separate branches for each sensor. It is possible that there are two separate internal supplies just in case one fails but in this case if the power supply failed most likely other sensors would not be working at this point. I highly doubt there are separate 5vdc power supplies for every sensor.
Nissan uses pretty compact ECUs so there isn't a ton of internal room for a bunch of separate power supplies. I believe I have a spare Nissan ECU in my garage maybe I can crack it open and take a look at the inside and see whats going on.
Kevin Pierson
awdeclipse 
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Posted: June 01, 2012 at 12:17 PM / IP Logged  
There are multiple 5v supplies,(all be it on the same chip most times) I.E. more then one pin on the ECU connector that is "5v sensor supply" and of those there are at least 2 discreet/separate/isolated 5v sensor supplies. What is the point of redundancy/safety if you only have one 5v supply? Pedal has 2 POTs both of which are fed from separate supplies. (in case one fails, or gets shorted to GND for example)
(Not sure if I understand your statement about this one but this is how I interpreted it)Each sensor has a separate 5v feed, but it comes down to where in the harness does the splice occur. This is why I said you can't simply cut the wire at the ECU and run a new 5v supply to the pedal because that wire is feeding multiple sensors. So if one of the power supplies failed or a 5v sensor wire was shorted to ground then yes, you would have multiple sensor failures occuring. (Still won't damage the ECU under most circumstances as power stages are short circuit protected (The ECU will shut down the powerstage output to protect it from overcurrent))
Opening up an ECU isn't going to get you very far (besides curiosity, and the occasional head scratching of course along with the fun factor). I have both pryed open and seen the guts of plenty of them from Micro Hybrid style to standard PCB, Port Fuel, Direct Injection, Gasoline and Diesel. The components handling the power supplies are typically some I/C with multiple tasks, (5v power supply and regulator, 12v supply and regulator etc.) Not gonna find any simple 7805s in there or anything that is a standalone regulator.
Agreed, not a bunch of room for "traditional" power supplies. But when you have I/Cs that are 40+ pin surface mount chips doing 10 different things, 5v supply is nothing compared to the rest of its tasks.
KPierson 
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Joined: April 14, 2005
Location: Ohio, United States
Posted: June 02, 2012 at 8:50 PM / IP Logged  
I took apart a Nissan ECU from a 2005 G35 coupe (should be very similar to Altima ECU) and found that there are at least two different 5vdc power supplies. The first power supply powers one APP pot and both throttle position sensors (which I find odd). The second power supply powers the other APP pot, the EVAP pressure sensor, the refrigerant pressure sensor, and the power steering pressure sensor.
The common 5vdc feeds are shorted together on the circuit board and every sensor has a dedicated wire directly from the ECU, with the exception of the TPS - they ran one power wire to the throttle body and it looks like it splits there.
And of course I wouldn't expect to find any 7805s on the board - I have never seen an automotive grade 78xx regulator! :)
Kevin Pierson
awdeclipse 
Copper - Posts: 285
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Location: Michigan, United States
Posted: June 04, 2012 at 7:55 AM / IP Logged  
Interesting. Much different then what I have been working with.
I have seen the throttle pots same way, both on one 5v supply.
Also interesting to see that all the "5v splices" are actually done at the ECU (each sensor power has a dedicated pin)as opposed to in the wire harness. I stand corrected!!
FWIW I was speaking about my experience with GM ECUs
Who is the supplier/mfg of that Nissan ECU? Denso?
KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: June 04, 2012 at 11:43 PM / IP Logged  
It's made my Hitachi (http://www.hitachi-automotive.us/products/Control_Units/ECU/index.html).
There seems to be one "main" power supply - an ST L9762-BC which I can't find a datasheet for - just a few pages referring to it is a Nissan ECU power supply chip that commonly goes bad. I would assume this chip also powers all the logic chips on the board, and was able to confirm that it is powering at least the main processor on the board.
The other 5vdc power appears to come from a tiny SOT-363 (or similar). It had a few letters on the top but I couldn't make them out and ended up scraping them off trying to get rid of the conformal coating on top of the chip. The chip has 6 pins, but two of them are tied together and connected to the 12vdc power plane. One of the pins then goes to the 5vdc outputs on the terminal strip. The remaining two pins go to ground and to the main power supply chip which has me thinking that this is a transistor and that all power is in fact fed from the main chip.
The 12vdc main power input is interesting - (4) 2A diodes in parallel feeding (4) K3377 20A mosfets. The outputs of the fets are all tied in parallel to a large power plain that covers most of the bottom of the board. After further examination this actually isn't all that interesting. There is a lot more current going through the ECU then I had originally believed between the O2 heaters, the throttle body motor, and the variable cam timing solenoids.
The ECU is based around a Renesas 32 bit processor.
So after spending an hour looking at datasheets and researching it I can agree with your previous statement - nothing interesting on the inside!
Kevin Pierson
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