04 maxima po726-po345 limp mode loses 3rd gear any help apreciated

[toycam]

hello i am working on a 04 maxima 3.5xe 5spd automatic.it has 1 engine code po345 crank sensor tested wiring to sensor using alldata checked ok sensor checked ok but replace anyway did not change anything.it also has a trans code po 726 trans input speed malfuction/something like that used alldata tested for voltage ohms and ref signal wich it had at the ecm and the tcm.i noticed if i clear both codes as soon as i start the engine both return at the same time like there tied together and the trans when i drive it shifts 1st 2nd hits 3rd acts like you threw it in nuetral then you have to downshift to 2nd to go again otherwise leaving in 3rd just revs .any help apreciated cant afford to throw ECM-TCM at it without knowing it going to fix so would like to verify first ran and drove fine until the codes showed tranny never slipped or messed up before codes.i have read a couple things that said nissan trannys are common for losing 3rd when there in limp mode due to codes in the system.i dont know thats why i am asking just trying to fix any help greatly apreciate thank you

[Nahkapohjola]

Originally Posted by toycam

hello i am working on a 04 maxima 3.5xe 5spd automatic.it has 1 engine code po345 crank sensor tested wiring to sensor using alldata checked ok sensor checked ok but replace anyway did not change anything.it also has a trans code po 726 ...

First check charge voltage at batt, then check voltage at computer, using only computer gnd/+ pins. Has to be over 13.5 Volts at the computer(s).

Seems to be bad sensor and/or bad connection = 'bad' input signals causing computer to drop into Safe Mode... If this is the case, the code lottery machine(s) will keep u buzzy. Clean all connectors, check link below.

Run diagnostics and test also TPS; tranny uses TPS as input. Erratic signal can make tranny behavior funny. Engine uses TPS only when cold. See how it works /used to be, link below.

[toycam]

hey thanks for the ideas and help the lady took it to the dealership and here is what she said the fix was 1st the flexplate was out of round so they recomended it but she did not do it and they put a washer under the cranksensor saying that the signal going from closer then 1/4inch signal to 1/2inch signal was setting the simaltaneous codes causing limp mode.but a signal from 1/4inch to 1/2inch is ok.so another words the crank sensor was to close to a out of round flex plate.she did not do the flexplate they washered the cranksensor cleared the codes was good 3rd gear works again.so if you run in to this issue check clearances between your crank sensor and flexplate.thanks again

[Nahkapohjola]

Originally Posted by toycam

...so another words the crank sensor was to close to a out of round flex plate....

hmm. Of course the gap is crucial but How does a fixed mounted sensor 'move' too close?

Not possible. This whole story starts much earlier, the hidden part I - from earlier jack the mech - isnt revealed yet...

[toycam]

because the flexplate was out of round.the sensor was fine.i found out from the lady that it had been to a tranny shop previously so i think they f*%kd up the flexplate somehow.dont know how seems like it would be tough 2 make a flexplate out of round.hey thank you again for all the input and help