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my 1999 XJR starts out in third gear, and won't down shift or up shift. Have new code latched up "P0730 Gear ratio incorrect". The speedometer works correctly. I've had wheel sensor faults before but they never created this problem. Is there a transmission input shaft sensor that fails on the 722 transmission?
Thanks,
Mike
According to the info in the Jaguar fault codes table, when P0730 is detected, the transmission will go into limp home mode (only 3rd gear and reverse, I believe) and the engine power will be limited. The table states only two causes:
This is just my personal experience with these Mercedes transmissions. Before you go any further into diagnosing, if you can get the car on a lift or up on jack stands, remove the grayish colored heat shield from underneath the car between the catalytic converter and the transmission. There’s a wiring harness that goes into the transmission. There’s a round plug with wires that I believe you turn CCW. After you disconnect the plug from the trans, inspect the male and female plug for oil intrusion. If there’s oil in there, I’d use a liberal amount of brake cleaner and compressed air to blow it completely dry. You can use dielectric grease if you have some. Reinstall the plug and button it up. Next thing I would do is clear the transmission code and perform a hard reset. After that check trans fluid level. Drive the vehicle like before and see if the same code returns and report back here. If it’s been a few hundred miles (🤷🏼 or more with no issues, then I’d say it’s ok. If that’s the case, replace the electrical socket that comes with new seals in it where the plug goes into the transmission.
Agree with Addicted2boost. Check the connector for fluid contamination. If after cleaning this and clearing codes the problem reoccurs you may have an issue with the conductor plate located inside the transmission mounted to the top side of the valve body. We see these fail often causing a "limp home" condition. Not too difficult to change once the car is in the air.
10-21-2020 | 06:22 AM
P0730 Gear ratio incorrect
or more with no issues, then I’d say it’s ok. If that’s the case, replace the electrical socket that comes with new seals in it where the plug goes into the transmission. 
