ran power wire now i got error lights

Last night I installed a power wire in my 08 Altima.. Here is the chain of events..

I removed the cover to the left of the dashboard, I removed the fusebox cover so I could take the screw out, I pulled the lower panel off, I popped out the ODBII reader, I unhooked the trunk wire, and unscrewed the other screws that were holding the lower panel..

I got my knife and started cutting out the carpet near the grommet.. I then cut the grommet and poked my screwdriver through it..

I pushed the wires through with a hanger and then had to remove the bottom of the airbox to get access to the wire..

That was all last night.. I left the car all torn apart because I was going to run some more wires today.. My wife needed me to go somewhere in a hurry this morning so I had to hurry and try and put it back together..

I didn't put any of the paneling or anything back on.. I just moved the wires that were in the way out of the way.. I went to put the airbox back on I noticed a piece of tubing was off.. I posted a question asking what it was and they said it was coming out of the CVT..



So I put that back on the nipple and clamped the box back on.. When I started the car it lit up:

TCS Off
slip
Service engine soon..

These are the errors I got:

P2138
Type PowerTrain
Status Stored
ECU $7E8
Description Throttle/Pedal Position Sensor/Switch "D" / "E" Voltage Correlation


P2127
Type PowerTrain
Status Stored
ECU $7E8
Description Throttle/Pedal Position Sensor/Switch "E" Circuit Low Input

I tried unplugging the negative for over 30 minutes but got the same thing when I started it up..

One other thing.. I noticed this plug but I don't think it's supposed to be plugged into anything..



Any ideas.. PLEASE!?!?

Thanks

The only thing I can think that could have possibly happened was I knicked a wire in the gromet hole while cutting (don't think I even came close to anything though)..

Or, when I had the guts laying out under the dash I may have shut the door and crimped a wire?

Could either of these possibly cause this error?

Found this but don't know what the hell to do about it..

P2138

P2138 - Accelerator Pedal Position Sensor Circuit Range/Performance

Possible causes
- Accelerator Pedal Position Sensor harness is open or shorted
- Accelerator Pedal Position Sensor circuit poor electrical connection
- Faulty Accelerator Pedal Position Sensor
- Faulty Electric Throttle Control Actuator
Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P2138 Description
The Accelerator Pedal Position (APP) sensor is installed on the upper end of the accelerator pedal assembly. The sensor detects the accelerator position and sends a signal to the Engine Control Module (ECM).
Accelerator pedal position sensor has two sensors. These sensors are a kind of potentiometers which transform the accelerator pedal position into output voltage, and emit the voltage signal to the ECM.
In addition, these sensors detect the opening and closing speed of the accelerator pedal and feed the voltage signals to the ECM. The ECM judges the current opening angle of the accelerator pedal from these signals and controls the throttle control motor based on these signals.
Idle position of the accelerator pedal is determined by the ECM receiving the signal from the accelerator pedal position sensor. The ECM uses this signal for the engine operation
such as fuel cut.


Read more: https://www.nissanhelp.com/diy/obd_codes/p2138.html#ixzz1w85Ze9FO

I would check the wiring going to the APP. Your vehicle has an electronic throttle and the accelerator pedal is basically two separate potentiometers that generate different, but correlating, voltages. From the faults you posted it appears as if you have lost one of those voltages (which also most likely means the car is in limp mode and not safe to drive).

The wire from the APP should go directly to the ECU and most likely does not go under the hood (I believe the ECU is under the passenger dash but I could be wrong).

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Kevin Pierson

Thanks so much for the reply. Where is the APP?

youd be amazed at the amount of damage that a coat hanger can do to a wire harness. if its telling you there is something wrong with the accelerator pedal but you didnt go anywhere near it then you probably shorted some wires out either with the coat hanger directly or with the knife when you cut through the grommet.

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Ugh.. That's what I'm afraid...

Say I did do that.. How would a mechanic fix that? I mean, it's tight as hell with zero slack to even do anything..

I'm so scared this is going to be a thousand dollar repair..

Thanks for the reply.

as far as checking and confirming the problem of exposed wires i guess you could use a snake camera to get a closer look. fixing it is just a matter of how many parts need to be taken out so you can have access to the harness and tape up any exposed wires. thats if you are lucky and didnt permanently damage the ECU.

also, that plug that you didnt think goes anywhere, it probably goes somewhere because they usually tape the plug to the harness if it isnt being used. being that it is a single, heavy gauge wire, it is probably a main power wire for something. i would definitely investigate a little more because that might be your whole problem.

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tbird2340 wrote:

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Thanks so much for the reply. Where is the APP?

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The accelerator pedal is the tall skinny pedal next to the wider brake pedal.

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Kevin Pierson

LOL. Thanks!

So the APP module is on the pedal than.

tbird2340 wrote:

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LOL. Thanks!

So the APP module is on the pedal than.

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Yes. It is more a pedal though and less a module. As I said before it is just two potentiometers that turn the position of the pedal in to two voltages.

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Kevin Pierson

https://www.nicoclub.com/FSM/Altima/2008/ec.pdf
'08 Altima factory service manual, engine controls.
start at page 420, break out the multimeter, there will be testing to do.
Mark

Thanks a lot for that manual.. I think this is too much for me.. :(

The manual says connector E40 but doesn't even say where or what it looks like..

I mean, I've done around 40 remote starts but I don't think I can do this.. I mean, unless someone thinks it can be something besides a nicked / cut wire because if it is all this testing is for not, right?

I was only in that one area near the grommet / firewall.. I only unplugged and unscrewed modules that were attached to the bottom panel under the steering wheel..

Someone on another forum said it may be $2,000 because they won't replace / fix the wire(s) with the problem. That they have to replace the entire harness.. I feel like I'm going to puke!

What part of Ohio are you in?

Dealerships typically won't do troubleshooting down to the individual wire, however, auto mechanics will. In all reality this isn't that complicated. Find the wire diagram for the APP - there should be 6 wires - 2 that are 12vdc, 2 that are ground, and 2 that are the signal back to the ECU. Measure all voltages at the APP with everything plugged in and with the ignition on. You should have 12vdc on the 12vdc wires, the grounds should be grounded, and the signals should change as you push the pedal down (remember ignition on, engine off). The point here is to find out where the problem exists. If everything tests find then the next step is to go to the ECU and measure the two APP signals at the ECU. Hopefully, by this point you have found an issue - if not there could be a damaged APP or ECU.

My only word of caution is that a drive by wire system is critical to the safety of the vehicle. If you feel like you are in over your head take it to someone who can diagnose it and fix it properly. The salvation here is that DBW systems are designed by the factory to be fail safe and the overall risk, even in a complete system failure, is really low (thanks to limp mode).

If you find that there is a wiring issue I would run new wire unless you can find exactly where the wire was damaged (which I would think would be unlikely). Check out what kind of wiring the factory used and mimic it (ie if they used 3 conductor shielded cable or a twisted pair or whatever use the same setup). The system is very particular to noise and voltage drop as the two voltages generated by the APP are constantly being compared to each other to detect system failures.

Lastly, the service manual has ALL the info you need, you just need to dig around for it. Typically there is a pg.pdf file that shows you were all the harnesses are in the car. The newer style manual is much more difficult to use the the early 2000 manuals.

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Kevin Pierson

I'm in the Youngstown area.. How about you?

Know any good mom and pop shop mechanics?

Dayton - It would be hard to be further apart and still be in the same state!

I don't know of any shops over that direction.

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Kevin Pierson

:(

You say to run tests with the ignition on but the engine off / car not running..

How do I do this with a push to start?

Thanks

To turn the ignition on without starting the car, Don't put your foot on the brake. Then press the start button twice. First press is accessory, second press is ignition. To turn off ignition, press button a third time again all without your foot on the brake.

I believe you can cycle the ignition on by pressing the button but not pushing the brake in.

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Kevin Pierson

Other vehicles I have worked with are one press / Accessory or press and hold, Ignition. Same as before, no foot on brake.

Correction?: APP should read (5v, Signal, GND) x2 for both Potentiometers in the pedal assembly. (this is based on my experience, haven't run into a 12v pedal) Also to note, all of these wires should go back to the ECU directly. 5v and Gnd is supplied from ECU, and "Signal" is the return to the ECU.

Chance of damage to the ECU is typically slim to none as they are intended to be short circuit protected. (Anything is possible though, especially if you were lucky enough to tag a 12v wire in the process) Make sure you have all the connectors seated well, some of them can be a bear to get them back in place.

If you have the pinout, check for your 5v and GND at each POT with ignition on. Once you confirm you have voltage supply @ the pedal, you can measure voltage between signal and ground and see if it increases as you push the pedal.

Don't expect the same voltage output from each POT, they are different for a reason. P2138 is the correlation fault between POTs. You could simply have a coincidentally bad pedal, or pierced a signal wire on POT1 or POT2 which is shifting the voltage seen by the ECU hence setting the correlation code. The service manual should give you a voltage spec at "Zero Pedal" for both POTs.

Also, healing pedal faults can be difficult. Either multiple key cycles with passing fault detection or a scan tool to clear the codes. If the pedal tests out as expected but faults are not clearing you may need a scan tool to clear the codes.

Well I had it towed to my mechanic so we'll see what happens.. He said he's fixed stuff like this before so hopefully he can figure mine out..

I greatly appreciate all the replies.. I just didn't feel confident trying to fix..

Well.. Got it back tonight. My mechanic said I was missing a 5V reference to sensor 2 of accelerator.. He said he just spliced into another 5V wire..

All lights are good and seems to be functioning normal..

Price = $150

tbird2340 wrote:

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Well.. Got it back tonight. My mechanic said I was missing a 5V reference to sensor 2 of accelerator.. He said he just spliced into another 5V wire..

All lights are good and seems to be functioning normal..

Price = $150

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so in other words he just put a band-aid on the symptom and ignored the actual problem... just a thought but did he even try to check for damaged wiring at the main harness where you were working? if not then the problem will most likely pop back up again and this time it will fry whatever other 5v source he tied into too.

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Yea, that's what I'm wondering / afraid of too..

I doubt he tried to check for the damaged wire because it would have been in the grommet which is damn near impossible to get to without tearing the car apart (guessing).

But to what you were saying.. If the problem was a cut or nicked wire and the problem existed up until the point he fixed it..

Wouldn't it have fried that other circuit he tied into right then?

He said the wire tested open (cut) so I'm guessing I should be fine..

More then likely there is only one 5vdc output voltage from the ECU for all the 5vdc sensors so nothing was "fried". What the mechanic should have done is tested for power at the pedal, then tested for power at the ECU on the same wire. I would assume there would be power at the ECU but not pedal. The mechanic then should have cut the wire at the ECU, spliced a new wire to it, and ran it to the pedal. My assumption is that you broke the wire in the grommet. This most likely won't be an issue, but if it is in fact broken then it could work its way lose over time, short out and cause the ECU to shut down. To prevent this from ever happening the wire should be cut at the ECU and insulated.

Also, do you know where he tapped the 5vdc feed from? If the mechanic used the other 5vdc feed that was going to the other potentiometer it would bypass part of the redundancy in the design of the DBW system. By design, if one 5vdc wire is broken or compromised the system should go in to limp mode and allow limited driving. However, if you use one 5vdc source to power both potentiometers and that wire gets compromised you will have no throttle ability at all.

That is awesome that you were able to get it fixed relatively cheap though!

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Kevin Pierson

ECU should have at minimum 2 - 5v supplies (upwards of 4-5). The pedal alone is operating on 2 separate supplies as was mentioned.

Without checking a wiring diagram, chances the the pedal has its own designated 5v is highly unlikely. It would be shared w some other sensor, whether it be a CAM sensor or the Throttle POT. So the idea of cutting the compromised 5V at the ECU and running a new wire isn't really possible, there are other sensors sharing that 5v feed.

Isolating the broken wire would be best but may not be possible without tearing the car apart $$$$. 2nd best fix would have been running a new 5v feed from the correct ECU pin and cutting the factory wire and splicing the new wire at the Pedal. This would maintain the dual 5v feeds for redundancy/safety.

I can not say as I blame you for you got lucky on an otherwise costly repair. I think the important thing is to understand how the repair was made and what potential impact if may have on future troubleshooting of the vehicle.

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.

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Kevin Pierson

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.

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! :)

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Kevin Pierson

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?

It's made my Hitachi (https://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!

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Kevin Pierson