How is CVT fluid changed? Full quantity or part of it?

[MalcolmY]

I vividly remember reading here that the correct way is to change what the nissan OBD computer says. The mechanic last time replaced all of it. Now my CVT is due for a new fluid,should I replace it all ?

[MalcolmY]

I have a symptom that is related and it's kinda scaring me. A couple of months ago my city was had a lot of rain so I have to drive in water a few times that night. Water was high but wasn't high enough to stop me. A lot of other cars couldn't start and stuck in the water. On the way home the problem started.

This problem only happens when I'm accelerating from a stop or from going very slowly. The engine doesn't respond to my input at all for maybe 8 seconds, doesn't get past 2000 rpm. And very very slowly it revs up until about 2600 rpm it returns to normal.

I had a few differential diagnosis (although they didn't know about the heavy rain): stuck throttle body that I have to clean. Or sensor near the throttle body or a problem with the input from gas pedal onward since this is a fbw has pedal.

As I'm typing this it occurred to me that maybe water got in the cvt through the axle joints since that's not a tight seal. Or is it?

I smelled the cvt fluid yesterday during an oil change and it smelled slightly burned. The guy was pushing to change it with dextron IV/V but I angryly refused (his argument was look this is a clear color liquid not red you can use this). How ever the car had it's last oil change around 49 Km ago so I didn't think much of that smell. It wasn't obvious. The color was definitely not green. I know the user manual recommends every 80,000 Km.

The last change was at 168,000 it's now 217,000 Km.


So I guess my questions are:

1. Did I drive too long before changing?

2. Is the symptom related to the cvt or throttle body or electrical?

3. The the maintenance PDFs say to replace all cvt fluid, during the car running empty through the inlet radiator hose and fill NS-2 until you see clear green. But some people here say it should be done with the help of the consult III. So which is it?

[AZhitman]

Welcome aboard, Malcolm!

Have you scanned for codes? Your accel issue sounds like the car is in limp mode, so we'll want to find out why that's happening first. You can scan for codes yourself - everyone should own a OBD2 scan dongle ($6 on Amazon) and the Torque app ($5 on Google Play).

Your #1 question, as you can imagine, can't be answered. Regardless, it needs to be changed.
#2, until you scan for codes, will remain unknown as well.
#3 - Both methods are acceptable. However, do NOT use anything other than the factory-specified CVT fluid.

[MalcolmY]

Thanks Azhitman

I literally just left the auto shop an hour ago, I wanted a OBD scan as none of my wired/wireless scanners could read a thing.

It they gave me two codes:

P0725 engine speed

P0868 fluid pressure low

I spent some time googling but I didn't understand what's up, but I know I'm in trouble as some people) nissan owners had to replace their CVTs with the the second code. My car is out of warranty, we don't even have the 10 CVT warranty anyway.

The car is not in limp mode, I experienced limp mode in the first months of owning this car, I'm the first owner. But I would describe it as really weak acceleration from a stop or low speed/low engine rpm. It happens intermittently and randomly every day now.

Does this mean a complete CVT rebuild? Or just replacing electrical components in the transmission? Could new fluid fix it?

I have a long trip coming up (1000 Km) should I be concerned?

[AZhitman]

Sounds like a CVT replacement is in order. Low fluid pressure usually indicates a valve body issue, and that would create the drivability symptoms you describe. I'll bet the P0725 code is secondary to the transmission issue, and would be resolved if the trans wasn't misbehaving.

[MalcolmY]

I will take the car in the next two days to a professional. Would you mind explaining why you think I would need a new CVT? Couldn't they just replace the valve body? Is there a crank sensor somewhere that needs to be replaced or do you think that too is secondary to the trans issue?

I will post an update once the car is properly checked.

[AZhitman]

The valve body, to my knowledge, is a major component of the unit. As such, they'd likely just replace the whole thing.

[And yes, I believe the codes pointing to the cam sensor issues are secondary to the CVT problem. Plan on replacing both cam sensors (they're not expensive). Besides, if your CVT is shot, you really don't need to worry about the cam sensors until it's fixed.]

All CVT transmissions from 03 to 10 got a warranty extension of 10 years or 120k miles. Did you check the transmission fluid level?

Reading back through your first post, I'm concerned about the water statement. How deep is deep? If you submerged the CVT vent or got water in a harness or solenoid connector, who knows what kind of havoc could have occurred...

Possible causes of the CVT code are:
- Pressure Control Solenoid Valve 'B' (secondary pressure solenoid valve) system
- Control Solenoid Valve 'B' harness is open or shorted
- Control Solenoid Valve 'B' circuit poor electrical connection
- Transmission Pressure Sensor 'A' (secondary pressure sensor)
- Line pressure control system

Those can be due to a faulty transmission, low coolant, low fluid, bad solenoid(s) or damage to the harness - possibly by water. The diagnostic process in the FSM is lengthy, and requires a Consult-II to perform:

DTC P0868 SECONDARY PRESSURE DOWN
The pressure control solenoid valve B (secondary pressure solenoid valve) regulates the secondary pressure to suit the driving condition in response to a signal sent from the TCM.

This is not an OBD-II self-diagnostic item.
Diagnostic trouble code “SEC/PRESS DOWN” with CONSULT-II is detected when secondary fluid pressure is too low compared with the commanded value while driving.

Possible Cause
Harness or connectors (Solenoid circuit is open or shorted.)
Pressure control solenoid valve B (Secondary pressure solenoid valve) system
Transmission fluid pressure sensor A (Secondary pressure sensor)
Line pressure control system

DTC Confirmation Procedure ACS002U1
CAUTION:
Always drive vehicle at a safe speed.
Be careful not to rev engine into the red zone on the tachometer.

NOTE:
If “DTC Confirmation Procedure” has been previously performed, always turn ignition switch OFF and wait at least 5 seconds before performing the next test.
After the repair, perform the following procedure to confirm the malfunction is eliminated.

WITH CONSULT-II
1. Turn ignition switch ON and select “DATA MONITOR” mode for “TRANSMISSION” with CONSULT-II.
2. Make sure that output voltage of CVT fluid temperature sensoris within the range below.
FLUID TEMP SEN: 1.0 - 2.0V
If out of range, drive the vehicle to decrease the voltage (warm up the fluid) or stop engine to increase the voltage (cool down the fluid)
3. Start engine and maintain the following conditions for at least 10
consecutive seconds.
VEHICLE SPEED (accelerate slowly): 0 → 50 km/h (31 MPH)
ACC PEDAL OPEN: 0.5/8 - 1.0/8
Selector lever: D position
4. If DTC is detected, go to CVT-151, "Diagnostic Procedure" .

Diagnostic Procedure
1. CHECK INPUT SIGNAL With CONSULT-II
1. Start engine.
2. Select “MAIN SIGNALS” in “DATA MONITOR” mode for “TRANSMISSION” with CONSULT-II.
3. Start vehicle and read out the value of “SEC PRESS”.
OK or NG
OK >> GO TO 5.
NG >> GO TO 2.

2. CHECK LINE PRESSURE
Perform line pressure test. Refer to CVT-42, "LINE PRESSURE TEST" .
OK or NG
OK >> GO TO 3.
NG >> Repair or replace damaged parts. Refer to CVT-43, "Judgement of Line Pressure Test" .

3. DETECT MALFUNCTIONING ITEM
Check the following:
Pressure control solenoid valve B (Secondary pressure solenoid valve). Refer to CVT-131, "Component
Inspection" .
Pressure control solenoid valve A (Line pressure solenoid valve). Refer to CVT-120, "Component Inspection"
.
OK or NG
OK >> GO TO 4.
NG >> Repair or replace damaged parts.

4. CHECK TRANSMISSION FLUID PRESSURE SENSOR A (SECONDARY PRESSURE SENSOR) SYSTEM
Check transmission fluid pressure sensor A (secondary pressure sensor) system. Refer to CVT-137, "DTC
P0840 TRANSMISSION FLUID PRESSURE SENSOR A CIRCUIT (SEC PRESSURE SENSOR)" .
OK or NG
OK >> GO TO 5.
NG >> Repair or replace damaged parts.

5. DETECT MALFUNCTIONING ITEM
Check the following:
Power supply and ground circuit for TCM. Refer to CVT-154, "Wiring Diagram — CVT — POWER" .
The TCM pin terminals for damage or loose connection with harness connector.
OK or NG
OK >> GO TO 6.
NG >> Repair or replace damaged parts.

6. CHECK DTC
Perform “DTC Confirmation Procedure”. Refer to CVT-150, "DTC Confirmation Procedure" .
OK or NG
OK >> INSPECTION END
NG >> Replace the transaxle assembly. Refer to CVT-224, "Removal and Installation" .

[MalcolmY]

The water was high enough to stop other sedans on the road, I would say it was probably 40 - 50 cm high. Sometimes I would have been stopped inside the puddle then move with the traffic.

Is is possible that the sensors on the outside of the trans be damaged only?

If I needed a valve body replacement should I look for one from the junk yard?

[MalcolmY]

Okay so I took the car to a number of mechanics, all of them agree that the transmission needs an overhaul. But I'm at crossroads and need advise.

I have two options, either I have mechanic see what crapped in the trans and replace those parts. $1350
Or I buy a whole used transmission (between $1050 - $1750) and install that, labor cost between $160 - $260.

I have a third option that I don't like, and that's to have the shops selling the transmission install it. That includes a one month warranty! But the cost for labor + 1 or 2 months warranty is higher than what mechanics charge. So I'm not considering it.

The problem is that these shops have no information about these transmissions, which cars they were on nor the mileage etc. I'm literally buying a random trans! All they can tell is that this fits X vehicle models 200X to 201X.

So what do you think?

[AZhitman]

I think I'd shop for a low-mileage CVT out of a wreck, and make sure there's a warranty on it. I don't think you;re getting out of this one for less than $1500, but that's a lot cheaper than a car payment.

If water got in through the vent tube, it'd cook the CVT in short order. Something we've learned here in AZ: Don't drive through standing water.