This is my 4th post after 10 months on this matter, if you include Reddit. After some time driving, whether it's 5 minutes or 30 minutes, the transmission gets stuck in neutral. The engine still spins but cannot shift. The conductor plate within the valve body has been replaced, which we believed was the cause, but it was not. I've been researching with my dad, who is a great mechanic, and he doesn't understand the issue either. The last thing I'd want to do is take it to a repair shop, especially since my dad has all the tools to repair the vehicle, plus many repair garages scam you anyway.

I drive a 2004 automatic. The transmission name is NAG-1 if that is important.
- Error code P0715: Invalid RPM/invalid engine turbine speed.
This was believed to be caused by the N1/N2 sensors on the conductor plate, but now it could be bad wiring or another bad sensor somewhere else.
- Error code P0730: Invalid gear ratio.
This is likely caused by the previous error since the car doesn't know when to shift if it doesn't know how fast the engine is turning.

Possible causes:
1. TCM error not cleared.
I'm currently looking into this, but I don't think I have an OBD tool that can do that.
2. Electrical failure inside or around the TCM.
Checking the transmission connections shows no fluid leaking or wicking up the wiring to the TCM. Maybe the TCM has a bad connection, or another sensor has failed.
3. The link between the mechanical parts and the TCM is bad.
It could be that a sensor or wiring outside of the transmission housing is bad. It could be because of overheating if the transmission dies mid-operation. This is a shot in the dark.

I'm not a mechanic, but if my mechanic father doesn't understand this issue, then it could be a huge and expensive repair. I've been doing a lot of research online to get to the bottom of this, and I should be able to repair it myself since I have all the tools to take the entire car apart.
If anyone has had a similar problem solved, knows how to repair, or has suggestions on what to do next, please let me know. I appreciate any comments or suggestions.

Thanks for reading.

 

P0715 is a can bus issue on the Crossfire. Read this post Number 13 in the thread P0715 and P0705
Click the links and be sure to read them.When you replaced the conductor plate did it come complete with new solenoids and sensors, or just the plate? Could be you reinstalled a bad sensor.
Have you scanned the wheel speed sensors or replaced any of them?

PS After going back and reading your other thread/post it may be best to find a good independent shop that specializes in European/Mercedes and have them scan the car and then clear the code. Be sure they put in writing the exact codes they found and use the correct Numbers not some description like " It's the speed sensor" Get the numbers. Good Luck!

 

Thanks for the info Zip. I didn't think to look behind the conductor plate or TCM. I'm sure you can tell I don't know much about electrical systems compared to the mechanical systems. As far as electrical diagnostics went, we tested the pins on the old conductor plate, and the N2/N3 (not N1/N2) sensors indicated a problem. The OBD specifically pointed towards the N2 and N3 sensors. I'll look into the CAN bus post and look for potential origin sources there.
It was a complete replacement of the plate, new solenoids, filter, gasket, and all. I did not check the wheel speed sensors; we only checked the conductor plate.
Do you know if there's some trigger that causes it, or does it just happen from a connection going bad?

The previous diagnosis and repair were made:


Red is where I need to look.
Green is the connections I checked.
Yellow is also what I tested with the proper power inputs, and replaced the Transmission Solenoid Assembly.

Let me know if this is correct. Thanks.

 

Contact Eric and Cliffin near Dayton and see what they say. Those guys have gone deeper into the Crossfire than almost anyone I know (exception would be Josh Chase in California or Rudy Compart in CHicago).

@xfClifford What do you think?

(I dont' bother learning about the automatic transmission, because I will NEVER own one.)

 

The CANBUS has been found to go bad at the splices because of corrosion. They are hard to locate. If you test at the PTC as in the referenced post you will know if it is bad or good. Don't go hunting until you have tested at the PTCM connection. All the CANBUS enters the PTCM at just that one connector, so it is easy to test entire system at the one point.
Good to see you have the wiring diagrams.
The Nag1 transmissions is the same the same as Mercedes 722.6 and so you can scan for Mercedes specific codes by entering 2003 Mercedes SLK 320. It is a R170 chassis. If the car was supercharged like the SRT6 you would scan as a 2003 Mercedes SLK 32.
If i can download a picture this info may help:

GOOD LUCK

 

I've read through your post and I agree that the conductor plate was the most likely cause of the issue. However, I can't see where you've cleared the original faults from the TCU. The transmission will not work properly until those original faults are cleared from the TCU, especially if it's been in permanent limp mode. If the transmission has been playing up for a while, you should also clear all the shift adaptations as well.

 

Totally agree! Ref my post #2. Required is a good scan, note all DTC and then clear codes.

 

That's what was weird about it: my car never entered limp mode or had a check engine light. The transmission just dies; it's an intermittent problem that can happen whenever. I would think that once an error code like this occurs, it should be manually cleared so the car will drive properly, but what do I know? When the plate was replaced, there were no error codes presented; the issue came back. Right now I'm looking into the CAN bus connections between the TCM, PTCM, and CAB and at splices S122 and S123 on the circuit diagrams.