P0720-QX70/P0500

B

Blkinfi13

Member
Location
Atlanta
Car
Qx70s 2017
Name
Robi
I just hit this today, the sequence happens only when i switched to manual, was very hot and the a/c was on. I let the car down, removed check engine seems fine but have already seen the P0720 and the resulting P0500.
i would like to get this fixed but whats concerning is i found a reddit report where someone fixed this($3800) and 2 years later its back.
i am at 80k miles, should i spend 4k and get it fixed at the dealership ?
I did a lot of trouble shooting and this clearly feels like an electrical issue to me.
Can the experts please weigh in and advice ..
 
Can someone look at this and advice if i should get it fixed with the latest part number at a dealer or specialized transmission shop with a new or remanufactured part ?
can i keep the car or should i get rid of it...
 
Turns out it was the TCM module and the mechanic looked at the document attached and said was the best one he could find with such details.
$ damage= 3500( parts + labor + tax), labor warrantied for 3 years, parts for 1..
Interestingly the dealership here said ...have to change transmission for 12k.
 
I've just returned to this site, and happen to have the same issue
My name is Willi and i've been here since 2020
This is my fourth FX/QX and i really wanted the 5.0
the QX is discontinued as of 2017 and i had to have one
preferably the Limited which i found along with 21" wheels
I'm very happy w the 3.7 and its hp, although the 3.5 was fine!
Here's my finding w the P0720 code, along with analysis for the transmission
the OBD showed no other codes, and i learned that the problem is not easily diagnosed
its a choice of trying the valve body, or the entire transmission
I used to do this stuff myself, but no longer able to!
First i had my tec change the fluid just to see
It did not change anything and the fluid seemed ok!
There is no way to see what the culprit could be w/o dropping the pan
So i went to Aamco thinking they are the experts ... wrong
i sure as hell won't go to a dealer, but Aamco quoted about $9k for a reman tranny
They would not consider the valve body, claiming the fluid showed metal shavings, which it did
Luckily, i found an excellent tec in DFW that really knows his stuff
He agreed w my analysis and i got the valve body from Nexenzo
here's the problem you run into, with sourcing the valve body:
There aren't many available and most are on Ebay in China
a refurbished one around DFW is $1,500 or more!
So the 650 from Nexenzo sounded good.
After talking w Justin about the process, i ordered the part for the AWD
This requires the appropriate pre-programming which he took care of!
He's a very busy man so it did take some extra days to get it to me!
Again, there's not much choice so i waited patiently and got it!
My new tec performed the inspection, and after dropping the pan
we could easily see what the problem was ... very bad buildup of gunk!
My Carfax showed no maintenance of the transmission from previous owner
the extra sludge likely added heat to the components and clogged the valves
Seems the speed sensor failed, and the car went into limp mode, only 3 gears
the tec was very aware, and flushed w extreme caution w his own methodology
yes the car is running fine! shifting better than ever before, especially down shift
Automatic transmissions are very difficult to diagnose, as it requires opening it up!
and using a reman part, if its wrong, requires starting over, and another 6 quarts
Hope this helps some others, from my pov this requires people w experience
 
I can add the cost:
Initial fluid change ... 300
Valve body reman ... 650
Service to replace ... 750
hours of research
 
Blkinfi13 said:
Turns out it was the TCM module and the mechanic looked at the document attached and said was the best one he could find with such details.
$ damage= 3500( parts + labor + tax), labor warrantied for 3 years, parts for 1..
Interestingly the dealership here said ...have to change transmission for 12k.
Click to expand...
Hey Robi!
Where are you with your QX?
did you sell?
i thought you have a 5.0
 
Has anyone looked at the attachment i put up here for the TCM diagnosis and options and labor costs, the mechanic said he loved the detail and even the bolt sequence was precise, the part numbers were exact, Hoping it can help others as well.

@Viking - just got the TCM repaired and seems to be running ok...HOWEVER...
looks like the mechanic forgot to put the Washer fluid bolt back so have a low washer fluid ....also after he got done the bluetooth module died, i tried all the debugging but looks like its not broadcasting Bluetooth....

Another thing, we got a new module from Infinity- NO programming was needed...
 
Last edited:
A new module cost you a bunch?
but you're guaranteed a fix
funny i also have a low washer fluid alert
but it was there before the TCM issue
glad you got it fixed ... i luv my 2017!

Sorry you didn't get more help with this!
but the remanufactured parts are often a hit and miss
Hope you came out good, you should keep the car
2017 is the last year made, i wanted the 5.0 but happy with 3.7
definitely more economical
 
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