P0729 and P1734 fault code

[Kevin309]

Hi i have a nissan np300 d23 diesel

i have this issue of going to failsafe after running 100kph, went to nissan and this code appear they deleted it and test drove at first, driving was fine until it reaches 110kph
Anybody experienced the same thing?
Btw im from philippines

 

[Old.Tony]

Welcome to the forum.

Have you changed any of the wheel sizes? Are any of the wheels an odd size compared to the others? These codes are gearbox codes indicating a problem with the gear selector and the ratio.

It might be happening because the output shaft revolution sensor is faulty (dirty connection, damaged wiring).

Does it happen if you leave the car in 5th gear?

 

[Kevin309]

Just changed to 18” wheels same with stock tires, where will i find those sensors thanks

 

[Old.Tony]

My apologies, I had thought you had a manual gearbox and was going off info I found in the USA. I've now downloaded the NP300 Service Manual so I can be more precise with my response and it doesn't list P0729 for the manual gearbox, only the automatic.

Is yours an auto? 7 speed?

If it's an auto, it lists a bunch of possible causes:

POSSIBLE CAUSE
• Input clutch solenoid valve
• Direct clutch solenoid valve
• High and low reverse clutch solenoid valve
• Front brake solenoid valve
• Low brake solenoid valve
• 2346 brake solenoid valve
• Anti-interlock solenoid valve
• Each clutch and brake
• Output speed sensor
• Input speed sensor 1, 2
• Hydraulic control circuit

And that's all stuff that should be looked at by an auto transmission specialist. Not your average mechanic, and perhaps definitely not by a dealer mechanic.

P1734 is the same error but for 7th gear.

It's possible that you've had some contamination in the gearbox - if you can check the oil, look for any discolouration (milkiness, or particles). Otherwise, if it was my car, I'd take it to an auto transmission specialist.