Hey everyone,

I purchased my 09 G37 X AT back in November. I noticed once I drove away the car would slip when shifting in sports mode and also my shifter assembly felt loose. Never had an issue with the car until about a month ago I hit a bump and the linkage bushing and broke and my car wouldn’t engage at all. Towed it home and replaced the shifter busing and the car started working again with out an issue. About 4 day’s ago I drove up my drive way and put the car in park and for some reason the cluster started notifying me to put the car in park which it was already engaged. Did some research unhooked the battery for 10 minutes and still having the same issue. I noticed there is a white plastic tab that moves up in the assembly that I have to push up for the car to recognize it’s in park. Ordered a new shifter assembly and will be here later this week. I then took the car to fire stone to get my CEL scanned and I got a P1721 code. The tech was unable to tell me if it was the input or output speed sensor. This is where I’m lost, I found a speed sensor online for $80 but I’m not too sure if it’s the right one I need. I also can’t located the speed sensor at the tail of the transmission so I can’t tell if the replacement part I found is the right one. Any help would be greatly appreciated. (Pictures will be followed to show which tab I have to push up to engage it in park)

thank you!!

 

The speed sensor plugs into the transmission control module (TCM), which is located above the valve body inside the transmission, above the trans oil pan.
I think the speed sensor can only be replaced with transmission removal and disassembly.

Without special tools that support enhanced diagnostics, I don't think this is a DIY fix.

The P1721 code is set when:
• The vehicle speed transmitted from the unified meter and A/C amp. to TCM is 5 km/ h (3 MPH) or less when the vehicle speed detected by the output speed sensor is 20 km/h (12 MPH) or more. (Only when starts after the ignition switch is turned ON.)

• The vehicle speed detected by the output speed sensor does not decrease despite the 36 km/h (23 MPH) or more of deceleration in vehicle speed received from the unified meter and A/C amp. when the vehicle speed transmitted from the unified meter and A/C amp. to TCM is 36 km/h (23 MPH) or more and the vehicle speed detected by the output speed sensor is 24 km/h (15 MPH) or more.

Possible causes:
• bad TCM / valve body
• bad unified meter & A/C amp
• broken / shorted wire or connector

If you want to learn more, do an online search for the factory shop manual and look for section "TM"
Good luck with what ever you decide to do.

 

Thanks for the help, i took it a Infiniti dealer and they were unable to get speed sensor code pulled up. Not too sure if fire stone did something different. I was able to replace the shifter assembly and I stopped getting the alert to put the car in park. Thank you again!

 

You are welcome and thanks for the update. Too often, I try to help and don't know what the fix was.