These CVT transmissions have been around long enough that there should be more than “buy a new one” from mechanics. Seems Nissan holds detailed operational engineering details so close that I’ve yet to find anyone who truly understands what goes on with solenoids, pulleys, and stepper motors.

So, when ANYTHING goes wrong, the answer is “replace the $3000+” CVT.

I’m not believing thats the only answer after having a few of these.

Mine went from strange shifting occasionally to an inability to shift properly shortly after I lost the bottom of the front bumper and undercarriage cover at the beginning of summer. It had P0841 DTC until I changed fluid twice and now has added P0965 P0776 P0746 to the list. Curious.

I’ve developed a few hypotheses as to what might be going on and how a valve body replacement might be the answer. First, I’m looking into how I can inspect the drive belts while it’s on the vehicle before I hang my hopes on a valve body replacement cure.

Hypothesis #1 - The drive belts aren’t ruined. If the drive belts were worn too far, I wouldn’t get acceptable performance when temperatures are low. If the belts were worn, they’d always slip, not only slip when warm/hot.

Furthermore, the behavior is more like being in a “gear too low” than slipping. I get high RPM, with rapid deceleration after easing the throttle and, at times, engine laboring to stall as in being in a gear “too high.” These would be issues with incorrect pulley ratios and not slipping behavior. If the belts were slipping, there’d be insufficient traction to cause deceleration in low or stall the engine in high.

Hypothesis #2 - pulley ratio changes are compromised by heat degraded coils or motors. As fluid ages, it’s ability to cool the electrical components (coils and motors) in the valve body that govern “shifting” is compromised. In a vicious circle, hot fluid degrades more rapidly, resulting in higher temperatures, accelerating the degradation. The coils and motors degrade concurrently as it all runs much too warm.

Temperature degraded coils commonly function adequately until ambient temperature increases, then becoming weaker and fluttering. Anyone who’s replaced a coil to fix a Kenmore gas dryer, or worked on a pinball machine is familiar with these phenomena. So a P0776 or P0746 DTC is consistent with this sort of coil issue. “Ambient” in this case being that surrounding the components.

Hypothesis #3 - body design cools CVT. The ridiculously low clearance of the front bumper and undercarriage cover is required in order to channel air over the portions of the CVT that cool it. I’ve never seen this mentioned, but it seems that CVT issues begin after this happens as its been the case in 3 different Altimas that I know of.

Another common theme in these 3 seems to be delayed motor oil changes. Perhaps the elevated temperature of worn motor oil and it’s proximity to any CVT fluid cooler exacerbates the wear of CVT fluid which itself is already too hot.

Hypothesis #4 - gunk from overheated CVT fluid clogs channels preventing smooth flow. Obviously I don’t know the characteristics of the NS3 fluid over time and at temperatures and Nissan is guarding that as a state secret, but it seems NS3 has 4 purposes:

1) Cooling Components

2) Lubrication between some materials

3)Adhesion between other materials

4)Hydraulics


As it is overheated and ages, it separates into a goo and a thin liquid. Much like cholesterol in blood. When draining and refilling, the thin “blood” is replaced while only some if the goo/cholesterol remains and clogs channels.

This would explain the slowly improving behavior of my CVT after two fluid changes as well as the sudden new codes. It’s a cooler winter, so the goo remains and is working its way through the entire system hopefully settling in the pan.

Hypothesis #5 - another fluid change after allowing the fluid temperature to get very high may lower the viscosity of the goo and more will drain.

I would expect performance to be even better after that change as the channels would be clear and properly behaving fluid does it’s jobs.

A few points:

1) Yes It’s wishful thinking but it’s not entirely hope. There seems to be ample evidence this CVT could be rescued.

2) Behavior is steadily, if slowly, improving after two fluid changes

3) These are hypotheses, not facts, based on much observation, so please don’t blast me for arriving at erroneous conclusions.

4) Please DO explain, if you would, why my hypotheses are incorrect. That is one point of my post

5) Citing your experience along with a blanket statement that “it’s ruined” or “wrong”, isn’t helpful unless you explain what I’m wrong about. The other point of my post is to try and decipher what’s actually going on inside these CVT. It’s astonishing that there is so little understanding of how these devices actually work.

6) A link to a detailed treatment explaining their operation including what a coil, stepper motor and/or fluid does during operation would be most helpful as I’ve yet to find such information

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #1 - The drive belts aren’t ruined. If the drive belts were worn too far, I wouldn’t get acceptable performance when temperatures are low. If the belts were worn, they’d always slip, not only slip when warm/hot.

Incorrect. The only effect of temperature on belt pressure is if the front pump is worn and line pressure is dropping too far to clamp the belt or the LP solenoid coil is trashed and it can't regulate properly when hot. You need to inspect the belt with a borescope, you can't infer damage-or-not from behavior.

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Furthermore, the behavior is more like being in a “gear too low” than slipping. I get high RPM, with rapid deceleration after easing the throttle and, at times, engine laboring to stall as in being in a gear “too high.”

That's classic belt slip (as opposed to "judder"). The near-stall is most likely from an inability to properly control the Torque Converter clutch when you drop throttle and the unloaded belt grabs.[/quote]

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #2 - pulley ratio changes are compromised by heat degraded coils or motors. As fluid ages, it’s ability to cool the electrical components (coils and motors) in the valve body that govern “shifting” is compromised. In a vicious circle, hot fluid degrades more rapidly, resulting in higher temperatures, accelerating the degradation. The coils and motors degrade concurrently as it all runs much too warm.

Temperature degraded coils commonly function adequately until ambient temperature increases, then becoming weaker and fluttering. Anyone who’s replaced a coil to fix a Kenmore gas dryer, or worked on a pinball machine is familiar with these phenomena. So a P0776 or P0746 DTC is consistent with this sort of coil issue. “Ambient” in this case being that surrounding the components.

Correct. Over-temperature can also cause differential expansion of Valve Body components and thus compromise hydraulic function, not just electrical.

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #3 - body design cools CVT. The ridiculously low clearance of the front bumper and undercarriage cover is required in order to channel air over the portions of the CVT that cool it. I’ve never seen this mentioned, but it seems that CVT issues begin after this happens as its been the case in 3 different Altimas that I know of.

Air cooling of the housing is not a significant factor. Alties prior to '13 didn't necessarily have heat exchangers. With 2-port beehives and no exchanger, CVT overheating under load was common especially in warmer climates, and would quickly destroy the fluid when it occurred. Nissan realized around '10 that this was a mistake, they issued a bulletin and started fitting radiating trans coolers to cars with CVT-overheat complaints. As of '13, Alties all got 4-port beehives and heat exchangers.

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #4 - gunk from overheated CVT fluid clogs channels preventing smooth flow. Obviously I don’t know the characteristics of the NS3 fluid over time and at temperatures and Nissan is guarding that as a state secret, but it seems NS3 has 4 purposes:
1) Cooling Components
2) Lubrication between some materials
3)Adhesion between other materials
4)Hydraulics
As it is overheated and ages, it separates into a goo and a thin liquid. Much like cholesterol in blood. When draining and refilling, the thin “blood” is replaced while only some if the goo/cholesterol remains and clogs channels.

The only "goo" that occurs in CVT fluid is varnish, and it doesn't separate. There's are no bands and only the TC and F/R clutches to contribute goo-making material, so "ATF soup" analogous to an ordinary A/T never occurs. If your tranny has "goo" in it, then it's trashed, period.

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #5 - another fluid change after allowing the fluid temperature to get very high may lower the viscosity of the goo and more will drain.

See above. CVT fluid thins as it wears out. "Goo" of any sort means the fluid has combusted, not thickened. Any such tranny is essentially destroyed.

Thank you very much for taking the time to educate me

You're most welcome. With the chronic codes your tranny is tossing I'd be pretty sure your VB has had it, and the slip sounds serious enough that belt damage is likely. Unfortunately the pre-13's didn't have "judder detection" in the TCM firmware like '13-ups, so pulling the VB and inspecting the belt with a borescope is really the only way to be sure. However, the odds are against you, and that's a lot of effort only to discover the unit is dying. So arranging for a good used or rebuilt unit before it quits might serve you better. If you go with used, get the donor TCM with it (there are other threads here about why, but suffice it to say you'll save a lot of headaches).

The only conclusion I come up with on these cvts is take a black sharpie and black out anything recommended on servicing of the cvt in the owners manual. My 09 cvt failed at around 94k because I never serviced it. Didn’t know any better and trusted the dealer. These things need spill and fills at least every 20k, and more if your ocd like myself. The way my 09 was driven I was somewhat impressed it made it that long. Back then I was an account rep for Kentucky, Tennessee and Georgia, so that thing was ripping through the smokies and Cumberland gap on a weekly basis. When it acted it up it was sudden and just started whining/slipping. Fluid still looked and smelled good if you were doing an old school tranny fluid test. I’m sure that fluid had next to no viscosity which was the death of my cvt. Cvt fluid while expensive isn’t as durable as what Nissan wants you to believe so change it early and often and rest easy.

I30DAD wrote: ↑

Tue Dec 28, 2021 4:17 pm

Hypothesis #3 - body design cools CVT. The ridiculously low clearance of the front bumper and undercarriage cover is required in order to channel air over the portions of the CVT that cool it. I’ve never seen this mentioned, but it seems that CVT issues begin after this happens as its been the case in 3 different Altimas that I know of.
Air cooling of the housing is not a significant factor. Alties prior to '13 didn't necessarily have heat exchangers. With 2-port beehives and no exchanger, CVT overheating under load was common especially in warmer climates, and would quickly destroy the fluid when it occurred. Nissan realized around '10 that this was a mistake, they issued a bulletin and started fitting radiating trans coolers to cars with CVT-overheat complaints. As of '13, Alties all got 4-port beehives and heat exchangers.

If memory serves me the bulletin was only for 4 cyl Altimas. Was the 4 port beehives and heat exchangers after 2013 for V6 Altimas as well?

If my memory serves, the VQ35 CVT's all had exchangers from the get-go so it wasn't an issue. The QR25 Alties initially had the same setup used in the '08 Rogue and early CVT Sentras, and all those models ended up with bulletins. The only CVT's with 2-port hives that have been successful (at least in relative terms) are the dual-range planetary units in the Versa and B17 Sentra, because the planetary removes quite a lot of torque load from the belt. Since mechanical shear is the other factor besides temperature that breaks down the fluid, and since shear is proportional to torque load, those trannies can do okay without a cooler if (and only if) the driver isn't a leadfoot and temperature conditions aren't severe.

Regardless of any cooling components, there is clearly an airflow aspect of the front bumper and undercarriage cover that directs airflow over the oil and transmission pan. This, coupled with the fact that 4 different Altimas started to have CVT issues following the loss of the airflow, leads me to believe that it’s designed to provide nominal cooling. Why else would there be engineered intake ports on the front bumper and the substantial undercarriage cover.

If the design is not for airflow, then what utility is there in a ridiculously low front clearance and the plastic bumper and cover design? It seems the low clearance was a trade off in order to accomplish some function otherwise, why expose the bumper to damage as they do?

As a scientist, I always take the facts and hypothesize based on these facts and if there s a better explanation than nominal cooling through airflow, then what might it be?

VStar650CL wrote: ↑

Wed Dec 29, 2021 3:18 pm

You're most welcome. With the chronic codes your tranny is tossing I'd be pretty sure your VB has had it, and the slip sounds serious enough that belt damage is likely. Unfortunately the pre-13's didn't have "judder detection" in the TCM firmware like '13-ups, so pulling the VB and inspecting the belt with a borescope is really the only way to be sure. However, the odds are against you, and that's a lot of effort only to discover the unit is dying. So arranging for a good used or rebuilt unit before it quits might serve you better. If you go with used, get the donor TCM with it (there are other threads here about why, but suffice it to say you'll save a lot of headaches).

Please help me out here because the idea of incorrect ratios causing high RPM and misbehaving engagement of the torque converter seem to support issues with coils and belt(s) with enough traction on the pulleys to exhibit this behavior.

If the belt(s) were slipping as the torque converter remains engaged as the vehicle slows, the engine/torque converter wouldn’t have any resistance and wouldn’t labor. Seems that belt(s) with traction are engaging the slowing of the wheels to the torque converter. Why would a slipping belt hold the torque converter and drive pulley? Wouldn’t the two pulleys behave more independently with a slipping belt?

Similarly with the high RPMS. With misbehaving coils and pulleys, it is logical that they wouldn’t be at the appropriate ratios given the conditions. But if the belt(s) were slipping, the resistance from the wheels would not be transmitted using the belts to the torque converter/motor to drive RPM up. Why wouldn’t the belt(s) just slip, making the two pulleys behave somewhat independent?

I30DAD wrote: ↑

Thu Jan 13, 2022 2:21 pm

If the design is not for airflow, then what utility is there in a ridiculously low front clearance and the plastic bumper and cover design? It seems the low clearance was a trade off in order to accomplish some function otherwise, why expose the bumper to damage as they do?

Thanks to Bernoulli, airflow when the car is moving primarily enters from the radiator and exits under the vehicle, not the other way around. If you look at the way most Nissans are constructed, the result is hot air off the catalyst as well as the radiator flowing past the CVT, so except for the pan, much of the housing is exposed to air that's hotter than the CVT likes, not cooler. Some early 6-cyl CVT's did have aluminum pans with cooling fins, but they didn't do much and could actually contribute to over-cooling in bad or freezing weather, so they were eliminated.

I30DAD wrote: ↑

Thu Jan 13, 2022 2:21 pm

If the belt(s) were slipping as the torque converter remains engaged as the vehicle slows, the engine/torque converter wouldn’t have any resistance and wouldn’t labor. Seems that belt(s) with traction are engaging the slowing of the wheels to the torque converter. Why would a slipping belt hold the torque converter and drive pulley? Wouldn’t the two pulleys behave more independently with a slipping belt?

Similarly with the high RPMS. With misbehaving coils and pulleys, it is logical that they wouldn’t be at the appropriate ratios given the conditions. But if the belt(s) were slipping, the resistance from the wheels would not be transmitted using the belts to the torque converter/motor to drive RPM up. Why wouldn’t the belt(s) just slip, making the two pulleys behave somewhat independent?

I think you're confusing physical behavior with controllability. The belt won't follow Newtonian rules like a pool ball because there's a computer trying (but not succeeding) to control its misbehavior. What emerges from that interplay will be anything but predictable.

VStar650CL wrote: ↑

Thu Jan 13, 2022 6:17 am

If my memory serves, the VQ35 CVT's all had exchangers from the get-go so it wasn't an issue. The QR25 Alties initially had the same setup used in the '08 Rogue and early CVT Sentras, and all those models ended up with bulletins. The only CVT's with 2-port hives that have been successful (at least in relative terms) are the dual-range planetary units in the Versa and B17 Sentra, because the planetary removes quite a lot of torque load from the belt. Since mechanical shear is the other factor besides temperature that breaks down the fluid, and since shear is proportional to torque load, those trannies can do okay without a cooler if (and only if) the driver isn't a leadfoot and temperature conditions aren't severe.

Interesting thread here. Hypothetically speaking what fluid change interval would you use for a CVT that experiences high shear forces due to a leadfoot?

00pathyse wrote: ↑

Sat Jan 15, 2022 11:39 am

Interesting thread here. Hypothetically speaking what fluid change interval would you use for a CVT that experiences high shear forces due to a leadfoot?

The wife and I are perfect examples, I change our '13 Altie at 20~25K. You could even go lower than that if you add hilly conditions, very heavy loading, or any sort of trailering.