I have a 2017 Grand Sport with 7 speed manual transmission. Car has 40,000 miles on the odometer. While taking it out for a Sunday drive in between gears I got a one high rev and then the gear shift indicator on the dash went out and the check engine light came on. I pulled over and turned it off, waited a couple minutes and turned it back on and the gear shift indicator came back on but the check engine light stayed on. Came home and checked the code and a P0734 code came up and wouldn't allow me to clear it. Did some research and found it was way above my pay grade to fix it so I took it to a dealer. He had it for a couple days and called and said the gear position sensor needed to be replaced and it was on top of the transmission so it was 15 hours labor and would cost $4100. I started calling around to other dealers and the chevy dealer closest to my house said they could install it for $2700 so I had them do it. After it was installed they called and said it now is throwing a P0729 code and they couldn't fix it. I picked the car up from the dealer and the check engine light isn't on but I'm expecting it to come back on since they said it was throwing a code. I have called everywhere I know and no one will tell me they can fix it. I live near Cincinnati Ohio and I'm out of options. Do any of you know anyone that can help me or do you have any ideas?

 

That's scary that nobody will tackle this head on for you. They will gladly take your money for the initial fix but then leave you stranded with the subsequent code. .....Horrible!!! Keep us posted.

 

Exactly! They will gladly sell me a new transmission though!

 

Here's an older thread on that code.

https://www.corvetteforum.com/forums...lem-p0729.html
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sent you a pm

 

Thanks for the information. I found that thread and the dealer said they performed the diagnostic on it and that it needed the new gear position sensor which was installed. Now they have no idea what to do other than sell me a new Transmission. I have a call into another dealer that someone else told me has a good Corvette Tech. Hopefully they will help.

 

Tell the dealer that mis-diagnosed it to refund your $2700 and put your old sensor back on since it did not fix it. Then try Larry Mallot at Mccluskey Chev. See what he has to say.

 

Maybe try Corvette Care, a repair shop in Columbus. I’m having a different issue with my transmission or torque tube, and did some research. This was the nearest recommended shop I could find. Talk to Ryan, maybe he can help? My appointment is not until early July, they are loaded with work.
good luck!

 

I had the car diagnostics done at Kelsey Chev. and they were the ones that said the problem was the sensor. They quoted me $4100 to install the sensor. Checked with another dealer that said they would install it for $2700. Paid the first shop $500 for the part and diagnostic work then took it to the second shop to have the installation done. First dealer would say they didn't do the install and the second dealer would say they didn't do the diagnostic work so I'm screwed.

 

For whatever it is worth, here is an explanation from A.I., which gleans info from multiple websites on this very same topic:


The P0729 code in a 2017 Grand Sport Corvette with a manual transmission signifies an incorrect gear ratio in 6th gear. This means that the powertrain control module (PCM) or transmission control module (TCM) has detected that the transmission's output speed doesn't align with the expected value for 6th gear, based on the engine speed.
Here's a breakdown:

• What it means: The code indicates that the vehicle's computer is detecting a mismatch between the input speed (engine speed) and the output speed (transmission output shaft speed) when the transmission is expected to be in 6th gear. This suggests that the correct 6th gear ratio is not being achieved.
• Potential Causes:
  • Speed Sensor Issues: A faulty input or output speed sensor, or problems with the wiring connected to these sensors, can lead to incorrect data being sent to the control module.
  • Internal Transmission Problems:While less common in manual transmissions, issues with the transmission's internal components can still cause this code.
  • PCM/TCM Malfunction: The control modules themselves can also be faulty, leading to inaccurate detection of gear ratios.
  • Fluid Level Issues: While less common in manual transmissions, low or contaminated transmission fluid could potentially contribute to gear ratio problems.
• Symptoms:
  • Check engine light: The most common symptom is the illumination of the check engine light.
  • Performance issues: You may experience problems with shifting gears, especially getting into or staying in 6th gear.
  • Reduced fuel economy:Incorrect gear ratios can lead to decreased fuel efficiency.

Important Notes:

• Manufacturer specific definitions:While P0729 generally means an incorrect 6th gear ratio, the exact definition might vary slightly depending on the vehicle manufacturer.
• Not limited to automatic transmissions: While this code is often associated with automatic transmissions, it can occur in some manual transmissions as well.
• Professional diagnosis recommended: If you encounter this code, it's best to have a qualified mechanic diagnose the issue to determine the specific cause and necessary repairs. Sun Transmissions offers information on P0729 codes.

Troubleshooting Steps:

• Check the transmission fluid level:Ensure the transmission fluid is at the correct level and is clean.
• Inspect speed sensors and wiring:A mechanic can check the input and output speed sensors and their connections for faults.
• Consult a professional: A proper diagnosis using a scan tool is crucial to pinpoint the exact source of the problem.

It is strongly advised to address this issue promptly to prevent potential damage to the transmission.

 

Thank you for all this information. That is very helpful. I talked to the technician that installed the Gear Position Sensor and he said that when you put the car into 6th gear it indicates that it is in reverse on the screen and this throws the error code. He said that sometimes you can wiggle the shifter linkage and get the 6th gear to show on the screen. This is going to be a huge mess.

 

If he can "wiggle the linkage".....which by the way is not exposed....they should try the attached alignment procedure.

 

The gear position sensor senses the position of a magnet that is attached to the shift shaft. Sometimes the magnet has to be replaced. Once either magnet of the sensor is replaced, then a gear position learn procedure has to be performed.

Bill

 

Thanks Bill, that is great information. Is this magnet located inside the transmission?

 

Thanks, I'll give them a call.

 

I have found in my area NON Chevrolet shops that do good work on Corvettes. Have you tried to go outside the dealership problem?

 

I've called several different transmission shops and they won't touch it. Even called one that specializes in corvette transmissions and they don't deal with resolving error code issues.

 

Curious if you tried RPM? How about trying a corvette specialty shop, not a transmission shop.

@Bill Dearborn Bill is the magnet replacement a transmission-out repair? Or can it be done from the shifter console inside the car? Also wondering who can do the re-learn? Done with a scanner?

Just a shot in the dark but OP maybe try calling MacMulkin's service department. I'm thinking these guys see a of of corvettes and may have seen this before. Worth a shot. A call is free. Where do you live? There's no info in your profile.

 

OP.....Someone like RPM will rebuild the transmission but you need a shop to remove it which is a big deal. The shame of it is that anyone could drop the transmission, pull the sensor off, reposition the magnet, tighten the bolt, and be done. Dropping the rear cradle isn't hard but it is time consuming. Here is mine. I zoomed it in, the sensor is on the left on top of the transmission...



Buying used is an option. There are a fair number of low mile units from the Cars & Coffee crowd that felt compelled to show off and wrecked their car

Attached are two docs that show you what the sensor looks like/where it is in case you needed it and another doc regarding the relearn procedure. OP....You may want to ask the tech if they did the relearn.

Here is a YT video showing the teardown of a TR6070 which is the manual transmission in C7 Corvettes. Around 1:22 is the magnet. The guy calls it a "HUD Sensor" or something like that but it's the gear position sensor of which the HUD is one benefactor of the data. If I remember right, the bolt that secures the magnet tightens against a flat on the shaft. If that bolt loosens *just* slightly, it can move.

 

^^^ Wow good info. I gotta re-fill my coffee and take a look.

Looks like a transmission out, or transmission drop fix. Damn.