P07D9 Code: 2022 JT Diesel (Gear 8 Shift Incorrect Ratio)

[Hound]

Encountered P07D9 code, which translates to " Gear 8 Shift Incorrect Ratio ". The JT was using Adaptive Cruise Control (ACC) when the ACC stopped / messaged that ACC no longer possible. Then power dropped and the transmission seemed to slip. Could not get above 55 mph. A restart of the engine resolved the issue even though MIL still present. MIL eventually turned off. Curious of anyone else's experience with P07D9 code. JT is at the dealer now.

More from https://www.dtcdecode.com/Jeep/P07D9:

Jeep DTC P07D9
Make: Jeep
Code: P07D9
Definition: Gear 8 Shift Incorrect Ratio
Description: The Transmission Control Module (TCM) monitors for conditions which lead to an unexpected transmission gear ratio (e.g. slipping clutches, hydraulic or mechanical defects, etc.). The TCM compares the actual gear ratio (i.e. the ratio of input speed to output speed) to a minimum and maximum calibrated gear ratio value. The TCM performs this comparison while driving in a fixed gear, during gear engagement, and during shifting from one gear to another.

Cause:

• LOW FLUID LEVEL
• INPUT OR OUTPUT SPEED SENSOR NOT OPERATING CORRECTLY
• DOG CLUTCH A- SLIPPING
• CLUTCH B- SLIPPING
• CLUTCH C- SLIPPING
• VALVE BODY - STICKING SOLENOIDS
• TRANSMISSION

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[Almost]

So I had this issue in my JK not that long ago and it turned out to be the wiring harness going to the transmission shorting out on a bracket on the firewall. Given that it is intermittent and was solved by turning the jeep off and then on again I'm going to say your actual transmission is fine.

If they come back and tell you you need a new transmission I would question them on it. My dealer told me I needed a new transmission which they replaced under warranty only for them to call me 3 weeks later to pick it up and for it to go back into limp mode before I left the lot.

 

[Hound]

Almost, your analysis makes a lot of sense. Thanks for sharing. If the harness is not part of the diags, I will now ask for the harness to be inspected.

 

[Hound]

The technician felt the issue to be ATF running low by 1.5 quarts. The JT only has 9,300 miles, so the conclusion was that the transmission was underfilled at the factory. Low fluid is one possible cause for the P07D9 code.

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