P0797 Code, 2013 Black Edition with 63.000 kilometers

Hello,

I am a new owner of 2013 (US MY 14) Black edition GT-R new owner from Europe since last September. The car is completely stock and was never driven extremely hard (in the transmission oil temperature history there are no occurrences above 110C/230F and in the warning history also has no warnings for clutch protections, line pressure loss or high oil pressure).

The car now has 63,600 km, has always been serviced by the previous owner in a Nissan HPC, the transmission oil was changed at 55,350 km in 2019. As already mentioned I own the car since last September and only drove the car for aprox. 400 km since that. The car was put in storage since November 2022 and I only managed to go for the first ride this year last Friday, when I made a short trip of approx. 30 km (not a particularly sporty driving style). Maybe it is also worth noting that before shutting down the car on Friday after the drive (when everything was still fine), I erased some error codes (from the body control module - B2553, B2562, B2604 and B2617) with my ECUTEK ECU Connect, which were there after I changed the battery before putting the car in storage last year. On Saturday I wanted to take it for a drive again, but when I pulled out of the garage I noticed that the gearbox wouldn't shift into second gear. I then immediately stopped in a parking lot and switched the car off and on again, followed by the T/M System Malfunction Visit Dealer error message and the gearbox warning light flashing.

I then read the error codes with my ECUTEK ECU Connect and the code P0979-00 Pressure Control Solenoid “C” stuck came up (see Ecutek DTC file in the attachment). After that I tried to clear the code but the error message comes again. I then took the car for another 2 km drive and noticed that gears 1-3-5 and R work. After that I parked the car overnight and tried to delete the codes on Sunday, but without success - when I try to erase the code with Ecutek while the car is running, the car starts the self-diagnose in the bord computer and throws out the error again, although the DTC is cleared and not visible in ECU Connect anymore. The DTC reappears in ECU Connect only when I power off the car and start it again. I also tried erasing the codes by disconnecting the battery for a few minutes but also without success - the error message reappeared when I started the car after reconnecting the battery.

I then made a log with the Ecutek, but without driving the car, but just letting it idle in in standstill (see attachment). On Sunday I spoke to the previous owner, he said that a problem like this had never occurred before (which I tend to believe since the previous owner was very serious and accurate). The only thing I could figure out from the old invoices is that the input shaft seals were changed by the HPC at the same time, when the transmission oil was changed at 55,350 km.

Over the last few days I made some research on the internet about these kind of issues. I found the Nissan technical Handbook on NICOclub.cm (Nissan Service Manuals - NICOclub attachment TM, page 123-124). The most probable culprit should therefore be a failed Axis A feed pressure solenoid. If I understand correctly this would require opening the transmission.

This is copy from the handbook on P0797

DTC Self-diagnosis name

P0797 Pressure control solenoid "C" stuck on

DTC detection condition
• A DTC is set if the clutch A pressure sensor
value is less than 0.4 MPa (4.08 kg/
cm2, 58 psi) when the axis A feed pressure
target value is 0.4 MPa (4.08 kg/cm2, 58
psi) or more.
• A DTC is set if the clutch A pressure sensor
value is more than 0.2 MPa (2.04 kg/
cm2, 29 psi) when the axis A feed pressure
target value is 0.1 MPa (1.02 kg/cm2, 14.5
psi) or less.

Possible cause
• Axis A feed pressure solenoid valve
• Clutch A solenoid valve
• Clutch A pressure sensor
• Clutch A oil passage
• Harness or connector
(Open or short in the axis A feed pressure
solenoid valve circuit)
(Open or short in the clutch A solenoid
valve circuit)
(Open or short in the clutch A pressure
sensor circuit)

After watching some logging videos I also tried to interpret my log. If I understand correctly the Nissan description of the error code, I should be comparing the following two values from ECUTEK: Axis A Pressure Target (bar) and Clutch A Pressure (bar). In my log both values remain at 0, while on the B side Target is 10 bar, while the clutch pressure B remains at 0. The thing I do not understand is, why the DTC appears, since the Axis A Pressure Target is 0 which corresponds to the Clutch A Pressure and in my understanding should not throw a DTC if I apply the above mentioned rules from the Nissan handbook.

I also reached out to a german specialist (Importracing) who took a quick look at the trouble code an the log and told me the best would be to send the transmission to them for an overhaul (changing of all seals if I understood the correctly). That would be also my final solution if it turns out, that there is a problem, that would require the opening of the transmission. But after reading a lot of posts on the forums on this DTC (but also on the similar P2715 for the B side) I would like to be sure that this is not some electrical gremlin which I figured out sometimes can happen with these codes, sometimes also connected with the right TCM software. And if I understood correctly a HPC with NISSAN Consult III can also make additional tests with this software to test the solenoids. The thing that makes me suspicious in thinking this way is the fact, that it happened this quick after I bought the car (which naturally can be a coincidence also) and I was using the Ecutek dongle to read out data and erase error codes form the BCM - so maybe something of this caused my problems..

I would also like to know if it is safe to drive the car in order to make additional tests and logs. In particular I would like to hear some opinions on this kind of testing, that I found on this forum (P2715 Lost gears (issue/solved?) | Nissan GT-R Forum (gtrlife.com)) in the video in post #10 - starting the car in N instead of P to avoid reading the TM system and trying if the problem with shifting persists.

I would be grateful for any help reading the log and pinpointing the actual cause of my troubles - the main reason being able to decide where to take my car for further checks and possible repair, since both the nearest HPC and also a reliable company that I would enthrust with working on the transmission are quite a few 100km away from where Iive. I also wrote an email to Jacks Transmissions hoping they might help interpreting my log.

Many thanks and best regards

Marko