J30 Transmission "Self-diagnostic Procedure"

[ROT8TOR]

Hey guys, I'm new to J30's and to the site, so I must say in advance, thank you for your time. I've SEARCHED for the answer to no avail and am forced to ask.

I'm having a problem with my transmission wanting to shift down out of overdrive on the highway. I have the service manual from PDFTOWN.com and am trying to preform the "Self-diagnostic Procedure" that is on page "AT-37". On "AT-39", they cover what to do if the "A/T check" light does NOT blink. In otherwords, it will NOT communicate with the car.

In order, I have checked or changed...

TPS is at "4.50", inhibitor switch adjusted, A/T control unit switched.

If you guys can help with either of those problems, I would be greatly indebted.

[ROT8TOR]

Did I do something wrong, why won't anyone answer?

[yodawill2000]

Come on guys Ive been helping him and this no light thing is a stumper.

[ROT8TOR]

Ok, maybe I can make this easier...

What solenoid (A or B), or valve, or chip, or flux capasitor, tells the car to

STAY IN OVERDRIVE !?!?!?

[driverdriver]

I've asked the Nissan/Infiniti field tech members of this board to weigh in on this issue.

[yodawill2000]

Thanks Driver !!Rest assured Rot8tor.Stevie or some other tech will chime in soon.

Nico is all cool like dat'.

[ROT8TOR]

You guys are all worthy, I'm sure. It's just such a great car and I hate that it's not right.I know it's something small we're over-looking, that we'll all laugh at in the future. *I hope*

[alex61089]

I have the same exact problem and i could not figure it out at all... hopefully we can figure this out. because my transmission light keeps blinking

[ROT8TOR]

Our problems differ in the fact that your light blinks.

In your case, the self diag procedure should work.

[elwesso]

did you try this with the engine/trans warmed up??? 9/10 times owners dont warm the car up to operating temperature and that causes self diagnosis not to work!!!

When you say the TPS is adjusted to "4.5" what does that mean? It should be around that at WOT, but more importantly what is it set at idle?

[driverdriver]

WOT = Wide Open Throttle in case any one is wondering.

[ROT8TOR]

As far as the engine being warm, I've ran it up and down the highway SOooo many times... I've tried the procedure a dozen times with various mechanic friends around and nothing.

2, the car preforms magnificently... until it goes for 4th.

The idle is dead-balls-on 750.

TPS was set to 4.5 volts at idle. I thought I've done everything to spec.

Again, The question now to you, is...

What tells the car to stay in overdrive?

Solinoid "A" or "B"?

[ROT8TOR]

I just tend to believe it's a stuck valve or something internal in the trans itself

[alex61089]

i have tried the procedure with the car warmed up. Yes, my AT light does blink when i start the car up BUT when i proceed to the transmission diagnostic, I get NOTHING so our problems are one in the same

[elwesso]

are we talking about the actual 4th gear or are you talking about the torque converter lock up?

If it shifts into 4th but the torque converter locks and unlocks thats one story, or if it does not want to stay in 4th gear then thats a different problem.

Heres the story though, theres 2 shift solenoids that control the various clutches and internal workings.. Look at page AT 20, at the bottom it shows the reference of the shift solenoids to what gear position it should be in....

Long story short: if its shifting into 1,2,3 properly your shift solenoids are not to blame... More likely, its an internal issue somewhere and you probably are going to be looking at a new transmission.

[ROT8TOR]

" D R A T S ! "

I'm sorry.

Trust me though... I never give up and now that you depend upon me also... makes me want to solve this thing more.

[ROT8TOR]

I'll explain.

Picture getting up to highway speed (65mph).

As long as I keep accelerating, the car will go (and stay) in overdrive.

THE MOMENT that I release the gas it downshifts.

Its like the opposite is happening. I give gas, it up shifts, I let off it goes to 3rd.

Even at 45mph around town, it feels like its not wanting to cruise down the road, like it's got drag. Torquey.

[elwesso]

how many miles on the trans? Fluid condition and maintenance history?

honestly sounds to me like youre gonna be looking at a new transmission, i think its highly unlikely that its an electrical issue or a "simple fix"

[ROT8TOR]

10-12,ooo on transmission from what I was told at time of purchase. I've just bought the car, so I've just done a fluid'S change from oil, to coolant, to trans. Man, I just can't see it being toast. It drives great.

[Rex]

So, the car came with a "replaced transmission"? Did they say "rebuild", OEM re-manufactured or was it just new to this car (taken from another)?

Can't say for sure on a J30, but in the Q45, the AAMCO-type rebuild is no where near the same.

There's an outside possibility that it's a TCU issue, thus the diagnostics isn't returning any error??

[ROT8TOR]

They were older folks and had misplaced the paperwork, but told me Infiniti did it. I had no reason to call them liars and beat them to death, or I would've. I did call them to ask if this problem existed before and the old geezer said they never go on the highway. Classic, huh?Anywho, when I bought the car it didn't run (starter) and it had the title lost with the other paperwork... so this is where I'm at. Just starting down "J road".I know where they live and I can drive this thing right through their front porch, if that's what you suggest I do next.

[ROT8TOR]

When you say "TCU", do you mean the A/T Control Unit down by the emergency brake pedal?

If, "Yes", then, yes, I changed it out too.

[yodawill2000]

To add to this weirdness Mine was doing the exact same thing around 40 Mph (Hunting to third when I let off) and adjusting the TPS fixed it.

[GerryO]

I'll explain.

Picture getting up to highway speed (65mph).

As long as I keep accelerating, the car will go (and stay) in overdrive.

THE MOMENT that I release the gas it downshifts.

Its like the opposite is happening. I give gas, it up shifts, I let off it goes to 3rd.

Even at 45mph around town, it feels like its not wanting to cruise down the road, like it's got drag. Torquey.

So letting off the gas at freeway speeds causes the transmission to down-shift and engine rpms to increase?

It sounds like the TPS (a variable resistor) signal is communicated to the transmission from the ECM backwards.

BUT, just for drill (and easy and inexpensive to do), check for intake ducting leaks and clean the MAF too.

My '97 F-150 MAF was dirty and it affected shifting at all points (subtle engine misses) and OD lock-up (intermittent bucking like a bronco) at freeway speeds to the point that my first thought was that the transmission was failing.

Things felt better under harder acceleration and for a while I even turned off OD. It probably had to do with speeds and volumes of the air moving past the dirty MAF sensor.
Modified by GerryO at 7:24 PM 8/19/2009

[ROT8TOR]

Alright now, Big O, now we're thinking!

I too, had a 240z and guess you've gone thru a lot with it like I did, so I value your opinion and thank you for the input.

For the rest of you... I gave in and took the car to an Infiniti "specialist" being he has the right tools to comunicate with the car.

Can't wait till tomorrow to see how pissed he is.

[yodawill2000]

Hope he sorts it out..To all you guys.I saw pics of his J and dang its a SWEET J !!!White J with Hicas just works for me !!


Modified by yodawill2000 at 7:16 PM 8/19/2009

[alex61089]

ROT8TOR me and you have the same exact issue. If you do a search in the forums i actually made a thread about this and posted a video showing this. When keeping the gas on the pedal the transmission stays in 4th once i release the gas the slightest bit it downshifts and the engine rpms higher; i step back on the gas and it upshifts. It's annoying as %%#&!.

Because we have the same problem and the diagnostic seems to not work for both of us the solution must be the same.

I replaced my TPS with one from Infiniti of scottsdale and i've adjusted it to the proper voltage, but still. Same problem. Bought a reman MAF and still. same problem.Put old MAF on and still. Same problem.I've cleaned the throttles, changed the transmission fluid, air filter, cleaned the MAF and stillSAME problem!!!

I pray that mechanic has an answer so we can put this issue to rest. Otherwise than this problem the transmission shifts PERFECTLY.

[ROT8TOR]

ALEX, Good! Well, not "good" in the sense that yours is f#@ked up too, but "good" that it just wasn't me that was seeing the Transmission Ghost from Infiniti Hell!

Here's the thing we both need... Our cars have to talk to us!!

27 hours and counting and still NO word from the "specialist"... so obviously the J3o isn't talking to him much either.

SO....

I've got a guy, waiting in the wings, that's a transmission specialist. He thinks it's coming to see him next.

TO BE CONTINUED....

[alex61089]

well hopefully he comes up with something because i've been dealing with this issue for about 7 months now and i must say. it's annoying and if the transmission was on its way out i think it would of canned out by now knock on wood.. lol i'm thinking two things.Bad mass air flow.Or Rev sensor. I'm betting it's a rev sensor though..

[ROT8TOR]

I'm thinking solinoid "A".