Gear 6 Incorrect Ratio
The P0729 code means the vehicle's onboard diagnostic system has detected: Gear 6 Incorrect Ratio. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $200 - $3,000 (parts and labor)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light on
- Transmission slipping in 6th gear
- RPM flare during 6th gear engagement
- Harsh shifting into or out of 6th gear
Probable Causes (Ranked by Likelihood)
- Worn 6th gear clutch pack or band Very High
- Low transmission fluid level or contaminated fluid High
- Faulty shift solenoid affecting 6th gear Moderate
- Internal transmission mechanical wear Moderate
Step-by-Step Diagnostic Procedure
-
Check transmission fluid level and condition; dark or burnt fluid indicates internal wear
-
Monitor 6th gear ratio with a scan tool by comparing input and output shaft speeds
-
Test shift solenoids related to 6th gear engagement with a scan tool
-
Perform a transmission line pressure test in 6th gear to check for internal pressure loss
Frequently Asked Questions
What does incorrect gear ratio mean?
The TCM calculates the gear ratio by comparing input shaft speed to output shaft speed. When the actual ratio does not match the expected ratio for 6th gear, it means the clutches or band for that gear are slipping, causing power loss.
Can low fluid cause P0729?
Yes. Low transmission fluid reduces hydraulic pressure, which can cause clutch packs to slip. Check the fluid level first as it is the simplest and least expensive potential fix.
Is P0729 a sign the transmission needs rebuilding?
Not necessarily. While worn clutch packs require a rebuild, the issue may be a faulty solenoid or low fluid. Proper diagnosis can determine if the problem is electrical, hydraulic, or mechanical before committing to a rebuild.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0729 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Explore More
Was this helpful?
Share carcodefinder.com with a friend who needs to decode their check engine light.