P0729: Gear 6 Incorrect Ratio
What to do
Symptoms will show at a steady motorway cruise rather than around town — revs a little higher than they should be, or a sense of slipping when the transmission tries to take top gear. Have the fluid and line pressure checked before anything internal is discussed.
What this code means
The ratio measured across the transmission in sixth gear does not match what sixth should produce. Its odd position in the numbering — before the general P0730 rather than after the other gears — is simply because six-speed automatics arrived after the numbering scheme was fixed.
Sixth is a useful gear to have a fault confined to, because of when it is used. It is a motorway ratio carrying low torque, so a clutch that only slips there is a clutch that is failing under the mildest conditions it ever sees, which usually means low pressure rather than worn friction material. Read the full argument under P0730 before accepting an internal diagnosis.
Likely causes
Start here
- Low or degraded transmission fluid · easy
- Failed shift solenoid · moderate
- Worn valve body · specialist
Less common
- Low transmission line pressure · specialist
- Worn clutch packs · specialist
Symptoms
Components involved
Information, not instruction
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Community experience
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