J30 Transmission "Self-diagnostic Procedure"

[yodawill2000]

But Wes said if it shifts to first, second and third it verify s both Solenoids are working?

Wes and Rex and Q45Tech are freakin' Guru's As well as Stevie and a few others here.

[ROT8TOR]

Look, the one guy's tellin me (jumping early to a simple but costly solution)the transmission is trash and another is tellin me he's been driving like this for SEVEN MONTHS !?!?

C'mon! Maybe we can find a 3rd J3o that's had this problem. I find it hard to believe that 2 cars have the EXACT same 2 problems and WE are the only ones that don't know how to correct it?

*sigh...*

To ALEX; "Damn, man! I've only driven a few times in mine, for fear and lack of knowledge of the car and you've driven thousands of miles like that, damn."

To Yoda; "our objective here is to find a solution for the next sorry sap that has this annoying problem. Thus, the word "guru" must not be thrown around so easily."

R8R

piss: InfiniService's secretary just called me while I've been typing and said the tech needs the car one more day.

[yodawill2000]

And what really baffles me is had the exact same symptom and adjusting the TPS fixed it.Seems more than 1 thing can cause it then.The plot thickens !!!

[Rex]

Sorry if the question we're asking sounds like we're "beating on you", but not being there with the car makes it more difficult to trouble shoot.

I assumed the replacement trans was good, and asked about the TCU, b/c it can cause a similar issue to what you're describing. Heck a low voltage (weak battery, loose alternator belt, bad alternator) can create similar issues.

At this point, given the information you've provided, I think it's probably an electrical issue. If only I knew what was causing it???

[ROT8TOR]

Being I don't know, I'll ask, this has nothing to do with anything (yet), but...

Why are the drive shafts different between a '93 and '94?

Would it have to do with HICAS?

[yodawill2000]

Hmm.Rex might be on something.Everything on these Infiniti's is Electronic.~~Ponders~~

TCU has been replaced If I recall.If you follow the Q45 forum at all you will learn that the Guys that know the most are old school like I am .. Well kinda.Take their post with a grain of salt.Alot can be learned from them.Not only what the problem might be,But the thought process to properly diagnose a issue.Instead of and I quote."Throwing parts at it"

[ROT8TOR]

Electronic's are over done on this car. There are sensors for the sensors!

Which one has enough "sense" to stay in overdrive?

[SteveTheTech]

That is one of the things I really like about the J30 it is a challenge.

You describe it upshifting but I think the issue may be either closed throttle position related or the car is not actually commanding lockup. If they cannot get it to communicate you may want to open the case on the tcm and check for blue corrosion. My J had about 3/4" of shorted terminals causing enough costly issues to have the unfortunate owner sign it over to me. If you are having specialists check it I am curious to see what your line pressures and or stall test results are. (written before I read the whole thread)

I would love to have the tools to be able to correctly rebuild one of these RE4s but they are kept in the Nissan Museum and in some cases unit replacement is the way to go. But on the other hand I am with you on at least wanting to get to the bottom of your concern.

Without knowing if this is a shift control (ie mis adjusted closed throttle signal, or shift linkage) or a hydraulic issue from something like low pump output pressure not supplying enough line pressure to operate full torque converter lockup. I really hope you find one of the techs who is also interested in finding the route cause of your problem without wanting to charge your several hours to figure out what the problem is.

The RE4 and the electronic control of these transmissions although rudimentary by todays standards (the fsm for a 2008 G37 RE7 is proof) but can foil many experts who have done this for longer than many of us have been walking.

Without being able to drive your car I really do not feel like I can give you an honest answer. If I were to take your car down the street and experienced this I would repeat the same driving parameters in third to see if it was an input or something else. If you hold the throttle at ~1/8 throttle at a cruising speed the rpms should be roughly 2500 at 65 (if I remember my commute this morning correctly) and requires about 1/2 throttle for about 1 second to overcome full lockup. If your car is not going into full lockup the trusty multimeter will need to come out.

My J has its own interesting intermittent quirk that makes you realize your are driving a car that is as old as it is. When I have the auto climate control on whenever I need to pull across two or more lanes of traffic it starts off in third gear. I know it has something to do with the load signal calculation in the TCM but whenever I look at something like that it costs me a few hours and a couple bucks. You issue sounds like it needs some resolution. Also yesterday what I was driving out of my complex down a hill with a hard right at the end my power steering control unit shut off and that is a pin fit issue I thought I dealt with this past winter. It seems like you know what your doing in regards to this diagnosis and if you do not you know someone who does. I will try to come up with a few specific questions that might help you. The FSM is a great tool but if you follow it too a T it tends to lead you in circles and take much more time than it logically should.

The J is a great car when it is running well and in good shape but when it rains it tends to pour.

[yodawill2000]

heheTold ya Steve Rocks !!

Thank for dropping by Steve dude.We have a few J's doing this here so I'm anxious to get these guys sorted.Still cant help to think its TPS related, as I fixed it adjusting mine.But as with anything electronic, Curves will be thrown.

[ROT8TOR]

You said it early on in your "carography"... It's not performing lock up. So, what tells it to stay in 4th?

Driving my car would only want to make you buy it. It drives awesome.

I haven't seen it, but watch ALEX's video to see what it's doing.

Also... I asked earlier... Why are the driveshafts in the '93s different? Its bulkier, heavier and has some bolted up rubber contraption on it at the end towards the transmission.

[alex61089]

Yeah when I got the car it had about 148,000 on it now i'm up to 155,000 and I have not had any problems it's just not staying in overdrive when i let off of the gas.Perhaps he is on to something. It could be electrical related. Now i'm just giving a gander here but... Lets say your alternator isnt giving enough juice to the car. The TPS requires a proper voltage so because of this it shorts out. Causing this problem?

I have replaced the TPS TWICE on my car. One was from pepboys and the other one was from IOS.

Now i was reading something on some site that i can't seem to find anymore but someone was having the same problem and it turned out to be the REV sensor. Now as much as i want to believe this is the problem.. I'll be pretty pissed to pay 125 for this part and about 200 for labor to install it only to jump in the car and find out.. the problem still exists.

Fact of the matter is.. it MUST be something electrical or sensor related because my damn transmission light blinks every day when i turn it on. so something is telling the TCU "hey!!!!! somethings wrong!!!" Which has me sitting there like a baffled moron because This problem has existed since I bought the car and has seized to stop or be solved. Would a infiniti god please help us!!! lol

By the way. I gave up on taking it to mechanics.I took it to aamco and the guy basically told me to deal with it because he doesnt know whats wrong.I took it to my transmission mechanic and he looked at me like i was retarded because he's never seen anything like it and...I took it to my regular mechanic who hooked it up to a diagnostic and drove it with it running and STILL NOTHING CAME UP.His words "Sweet car; But #$@$$#@ up problem."

Oh how right he is

[GerryO]

It might help to think of it as all simple inputs and outputs. The ECM programming hasn't changed, so either the ECM is getting the wrong input information, it isn't processing it, a piece of hardware isn't receiving an output correctly or at all, or there is a hardware malfunction.

How many and what things change almost immediately when pressure on the accelerator is reduced? - the thottle plates close and less air is drawn through the MAF - intake manifold vacuum should decrease - the TPS output voltage changes to the stored "at idle" value

What else is physically connected to the accelerator pedal?

The car's speed shouldn't change very abruptly and changes in engine rpms would be a result of transmission downshifting. Has any work been done on the transmission? So the answer is...

Sorry I can't be of more help.

[SteveTheTech]

It might help to think of it as all simple inputs and outputs. The ECM programming hasn't changed, so either the ECM is getting the wrong input information, it isn't processing it, a piece of hardware isn't receiving an output correctly or at all, or there is a hardware malfunction.

That's it in a nutshell.

So I am sitting here eating my lunch and reading the AT section for out cars (96 model is much easier to read the >96). A few interesting tidbits that have until recently been overlooked.

The Revolution sensor on the rear tail shaft... This sensor is detectable but the TCM but if its analog sine wave doesn't match what the computer knows it needs to be TCC lockup may not happen. This does not indicate a sensor necessarily you may have good ole blue fuzz increasing the resistance in the circiut enough to cause an annomolly.

The Transmission Fluid temperature sensor. You may ask how could this cause an issue, what does at fluid temp have to do with lockup control. The answer is quite simple when you look at the detection logic of the RE4 control unit. Cold at fluid will cause TCC to slip and could potentially damamge something so the ever resourceful Japanese programmed the computer to NOT allow lockup when the transmission temperature signal is cold. Or below a certain point. AT-81 (96) gives you the resistance value for the atf temp sensor. I would check that if no one has looked at that.

One other thing I would check is the closed throttle position section of the TPS.

Oh crap I'll get into it more it's time to run to my car because its fixin to storm and my windows are open.

[yodawill2000]

Good stuff guys...One must let go of the old mechanical everything Drivetrains everybody.. well at least me..Grew up with.HAL runs this car..

[GerryO]

The Revolution sensor on the rear tail shaft... This sensor is detectable but the TCM but if its analog sine wave doesn't match what the computer knows it needs to be TCC lockup may not happen. This does not indicate a sensor necessarily you may have good ole blue fuzz increasing the resistance in the circiut enough to cause an annomolly.

The Transmission Fluid temperature sensor. You may ask how could this cause an issue, what does at fluid temp have to do with lockup control. The answer is quite simple when you look at the detection logic of the RE4 control unit. Cold at fluid will cause TCC to slip and could potentially damamge something so the ever resourceful Japanese programmed the computer to NOT allow lockup when the transmission temperature signal is cold. Or below a certain point. AT-81 (96) gives you the resistance value for the atf temp sensor. I would check that if no one has looked at that.

One other thing I would check is the closed throttle position section of the TPS.

Oh crap I'll get into it more it's time to run to my car because its fixin to storm and my windows are open.

I'm thinking easing up on the accelerator should only enhance OD lock-up, as compared to stomping on the pedal to cause a down-shift.

What does the transmission do when coasting down a hill at 60+ mph?

Easing up on the accelerator shouldn't suddendly change drive shaft revolutions or transmission temperature. What else is connected to/changed by accelerator pedal position, and did I read that the transmission auto-diagnositc procedure can't be run?

Could that be an indication of a problem with the transmission control module? Personally, I've never run the transmission auto-diagnostic.

[alex61089]

the diagnostic does not work for me or rot. Thing is though... he replaced his TCU and the problem still remains. The only difference between me and him is that his AT light doesnt communicate with him at all. Mine blinks everytime i start the car but yet when i go to run the diagnostic nothing happens... Maybe steve is on to something here with the fluid sensor.

The car needs to be properly warmed up for the diagnostic to work.. perhaps a malfunctioning sensor would tell the car that the transmission fluid is cold thus not letting the diagnostic do its job?.

Still doesnt explain why when i let go of the gas my transmission downshifts automatically and the rpms rise. I've tried driving in 3 but to no avail it still does it.

[ROT8TOR]

Hey guys, I've just got in for the day and have read what y'all were talking about with the temp sensor.

My Infiniti tech said that after "plugging-up" the car, NO system errors were found.

I told him to dwell on it over the weekend and he said he'd take it home and mess with it there. Driving the car, really does no good, I just think he wants to look cool.

LAST BUT NOT LEAST...

"Whats the dealio on my Driveshaft question? Why are "93s different from '94s?"

[SteveTheTech]

Easing up on the accelerator shouldn't suddendly change drive shaft revolutions or transmission temperature. What else is connected to/changed by accelerator pedal Personally, I've never run the transmission auto-diagnostic.

Drive shaft speed will not change quickly but Revolution sensor is basically tailshaft speed sensor with a fancy name. This is a vital input for OD operation.

The TCM does not allow TCC lockup when the transmission temperature is <120F. So if the signal from the sensor is indicating a low temperature but not low enough to trigger a fault code.

There is a kickdown switch attacked to the accelerator pedal. I knew there was something there but I have not seen an issue with that but it is basically like a brake lamp switch.

I too have lost my patience before getting the auto diagnostic mode to work. They are really particular.

I would not be surprised if none of you guys will ever get the tcm to produce a fault code since the system has very limited detectability of internal faults.

In order to do anything with this you are going to need a good multimeter and allot of patience. You will need to access the tcm and pin test almost every circuit with the exception of the Revolution sensor, unless you have access to a Hz capable meter or analog oscilloscope. The Consult II with the old communication cable has everything you need to view the common inputs so if you know someone at Nissan or Infiniti that can help you out that would save you serious amounts of time.

The complexity of these cars was one of the reasons that Infiniti actually provided every new owner with a pocket sized full copy of the ESM.

LAST BUT NOT LEAST..."Whats the dealio on my Driveshaft question? Why are "93s different from '94s?"

I have no idea it could be anything from the number of splines on the output shaft to the type of harmonic dampening devices used. I see pre 95 models so infrequently I do not have any idea what the difference is. Anyone have pictures only have the book as far back as 94.

[GerryO]

A kickdown switch tutorial (Porsche) that I found :

The automatic transmission is primarily controlled by internal hydraulic pressures. This includes the speed at which upshifts and downshifts occur, and the firmness of the shifts.

The kickdown solenoid is only one of several devices that adjust the control pressure to change the shifts. When the kickdown switch is made (closed), power flows from a fuse thru the switch, then into a terminal of the kickdown relay, thru the normally closed contacts of the relay, and out a terminal to the kickdown solenoid mounted inside the transmission. When the solenoid is energized, it reduces control pressure, raising the shift speed close to the maximum speed.

The kickdown relay doesn't do what most people think that it does. The power flow from the switch to the solenoid is thru the NORMALLY CLOSED contacts of the relay. This means that the power normally flows thru the relay.

In order to control the shift points more precisely (since the speed is very close to engine redline), the kickdown relay receives a signal from the tachometer when engine speed hits 5800 +/-60 RPM (USA and Japan - it's 100 RPM higher). This signal open the contacts in the kickdown relay, breaking the power to the kickdown solenoid. This has the same effect as instantaneously lifting your foot from the throttle switch, causing an instant shift. As soon as the engine speed goes back below 5800, the relay closes the contacts, lowering the control pressure to hold the next shift.

So, the kickdown switch supplies power to the kickdown solenoid only when the engine speed is below 5800 RPM. Above that speed, the kickdown relay opens, breaking the circuit.

Worth taking a look at the switch and the relay.

[ROT8TOR]

Ok Steve, here's the picture of the driveshaft.

[IMG][/IMG]

[IMG][/IMG]

Last week I went and found a '94 J parts car. Thats how I was able to change the TCU... I have 2 of everything but motor and trans. Ok, so, in the trunk was the drive shaft. At first I didn't notice it... but at second glance it looked slimmer. Lighter. So, I took out my driveshaft today and replaced it with the slim one and it works perfect. BUT... my shifting problem still exists. I know these have nothing to do with one another, but could this heavier shaft have to do with tearing up the transmission's in the '93s?

[yodawill2000]

And what really baffles me is had the exact same symptom and adjusting the TPS fixed it.Seems more than 1 thing can cause it then.The plot thickens !!!

[alex61089]

To be honest i think the 93 is just a big block of metal. These cars are so heavy the 220, or 210 at the wheels means nothing. My friend has a honda accord EX v6 and he burns me.. but when i think of it his car is light and little. Our J's are basically tanks in disguise lol.

[yodawill2000]

Thus the nice safety rating.

[ROT8TOR]

Alright guys, here's new info...

The J has since gone to my trans specialist.

He has just called and said it's the inhibitor switch.

???

TO BE CONTINUED...

[alex61089]

that makes no sense... i thought the inhibitor switch was the neutral safety switch? what could that possibly do with the transmission not locking up in overdrive

[SteveTheTech]

Thanks for the pic of the driveshaft. I still don't see the difference but something like a change in diameter would usually cause cross fitment warnings as we tend to err on the side of caution especially when installing used parts.

The inhibitor switch inputs the shift position to the tcm. If the proper voltage tests have been performed that may actually be the cause. If the car thinks it is in third when it is actually in fourth. However I do not think that is as high on the priority list as a tps or ctp sensor/switch that is within range but not correct would be.

The inhibitor switch actually has normallity verification in many modes as the primary output is to the tcm. The tcm has the ability to cross reference inputs to other inputs and known values to determine proper operation. This is simple technology by Infiniti standards but it is still surprisingly complex when compared to other models.

Throwing an inhibitor switch might not be a bad idea but are you going to be stuck with the part if it does not work?

At some point with some of these diagnosiseseseses the proverbial parts shot gun is required to get the job done. Sometimes you hit it often times it is nothing more than a miss.

I still think this car needs an old guy with a consult 2 to check the basics. Even some of the most experienced technicians in the field will find themselves running in circles and cursing at this classic car.

To be honest i think the 93 is just a big block of metal. These cars are so heavy the 220, or 210 at the wheels means nothing. My friend has a honda accord EX v6 and he burns me.. but when i think of it his car is light and little. Our J's are basically tanks in disguise lol.

I have thought about this exact dilemma although I am not sure where the power goes. Sometimes the thing takes off like a rocket, well an old rocket and for the day it was quick. Other days make you realize just how normal the acceleration can be. I think allot of the torque is spent in the broad gear ranges but when it reaches cruising speed it gets impressive fuel economy for the size and weight. You need to compare the J to cars from it's day it will run on an old ES or that other sedan and maybe that coupe thing from Lexus' in the mid 90s.I think a J with a stick would change the perception many people have of this car. If you want to try something that has impressive acceleration try a new G37S sedan.

[GerryO]

Alright guys, here's new info...

The J has since gone to my trans specialist.

He has just called and said it's the inhibitor switch.

???

TO BE CONTINUED...

Inhibitor Switch adjustment, Manual Control Linkage adjustment and Kickdown Switch adjustment are described on page AT-9 of the '93 FSM. There's also a reference to the "Electrical Components Inspection" for checking continuity of the inhibitor switch (page AT-79).

Diagnostic Procedures 12 (A/T does not perform lock-up at the specified speed) and 13 (A/T does not hold lock-up for more than 30 seconds) are on pages AT-68 and AT-69. Neither one mentions the Inhibitor Switch, but at least checking it doesn't involve removing the pan. Both list a Lock-up Control Valve that's inside the transmission.

Good luck in locating the one simple source of the problem.


Modified by GerryO at 9:02 PM 8/25/2009

[ROT8TOR]

Welp, that FIXED IT!

The beloved Inhibitor switch.

Didn't cost me a dime, took it off one he had, plugged it up and it drove like new. Even at lower speeds, the rpm's were much lower and the shifts were stronger.

Funny, I don't even know what one costs, but its well worth it.

Thanks for all your help guys!

R8R

[yodawill2000]

Killer news !!!

Need to source one out for backup.

[driverdriver]

Wow that's good!!!

Worth remembering.