Low or dirty transmission fluid (both sources; RepairPal lists low fluid level). Mechanical failure inside the transmission (both sources). Internal blockage in the transmission main control (OBD-Codes.com), or a transmission valve body failure (RepairPal). Faulty shift solenoid (OBD-Codes.com). Failed TCM (both sources) or PCM (RepairPal). Wiring issue (RepairPal).

Correct the fluid level, or change the automatic transmission fluid and filter, which RepairPal lists as the common repair. Repair any shift solenoid or wiring fault that has its own code (OBD-Codes.com, RepairPal). Repair a blocked passage or failed valve body / main control (OBD-Codes.com, RepairPal). Repair internal mechanical transmission damage (both sources). Repair or reprogram a failed TCM or PCM, only after the transmission itself checks out (both sources list control modules).

P0729🔧 Transmission / Gear ratioStop and fix promptly

P0729: Gear 6 Incorrect Ratio (Meaning, Causes, Fixes)

Q: What does P0729 mean?

P0729 means the computer saw the wrong speed ratio between the engine or transmission input and the transmission output while 6th gear was commanded, so it thinks 6th gear isn't working as it should. Both sources point first to transmission fluid and then to internal transmission problems; they differ on how severe it is and on which other parts are likely causes. OBD-Codes.com says P0729 can show up on vehicles with an automatic transmission when there is a problem shifting into 6th gear or while driving in 6th gear. The engine control module (ECM), powertrain control module (PCM) or transmission control module (TCM) compares engine speed against the transmission speed sensor to work out the gear ratio and torque converter slip; if the calculated value doesn't match the desired value, the code sets and the check engine light comes on. RepairPal describes the same check using two sensors: the input speed sensor tells the TCM how fast the engine is spinning, and the output speed sensor tells it how fast the transmission output shaft is spinning. If the TCM decides the transmission is not in the desired gear, the PCM or TCM sets P0729. It is a generic OBD-II code that applies to vehicles with a 6-speed or higher automatic, but repair steps vary by make and model. OBD-Codes.com says that if other transmission codes are stored, those should be fixed first. Related codes are P0730 (incorrect gear ratio) and P0731 to P0736 for the other gears.

Q: Can I keep driving with P0729?

Stop and fix promptly. Get it diagnosed soon and drive gently until you do. RepairPal rates P0729 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com gives no severity rating but notes the transmission may slip, shift late or not reach 6th gear, and that this kind of code usually needs advanced tools and skills. If the transmission slips or won't shift, avoid highway driving and have it checked.

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0729 means

OBD-Codes.com says P0729 can show up on vehicles with an automatic transmission when there is a problem shifting into 6th gear or while driving in 6th gear. The engine control module (ECM), powertrain control module (PCM) or transmission control module (TCM) compares engine speed against the transmission speed sensor to work out the gear ratio and torque converter slip; if the calculated value doesn't match the desired value, the code sets and the check engine light comes on. RepairPal describes the same check using two sensors: the input speed sensor tells the TCM how fast the engine is spinning, and the output speed sensor tells it how fast the transmission output shaft is spinning. If the TCM decides the transmission is not in the desired gear, the PCM or TCM sets P0729. It is a generic OBD-II code that applies to vehicles with a 6-speed or higher automatic, but repair steps vary by make and model. OBD-Codes.com says that if other transmission codes are stored, those should be fixed first. Related codes are P0730 (incorrect gear ratio) and P0731 to P0736 for the other gears.

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon and drive gently until you do. RepairPal rates P0729 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com gives no severity rating but notes the transmission may slip, shift late or not reach 6th gear, and that this kind of code usually needs advanced tools and skills. If the transmission slips or won't shift, avoid highway driving and have it checked.

Common symptoms

Check engine light on (OBD-Codes.com)
Delayed shift or not shifting into 6th gear (OBD-Codes.com); transmission may not shift properly (RepairPal)
Transmission slipping (OBD-Codes.com)
Loss of fuel economy (OBD-Codes.com); increased fuel consumption (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Low or dirty transmission fluid (both sources; RepairPal lists low fluid level)
Mechanical failure inside the transmission (both sources)
Internal blockage in the transmission main control (OBD-Codes.com), or a transmission valve body failure (RepairPal)
Faulty shift solenoid (OBD-Codes.com)
Failed TCM (both sources) or PCM (RepairPal)
Wiring issue (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Check the transmission fluid level and condition first. OBD-Codes.com says low or dirty fluid can cause shifting problems that affect several gears.
Read all stored codes. If there are other transmission codes, such as a shift solenoid circuit code, OBD-Codes.com says to fix those first, because an electrical solenoid fault should set its own code.
If P0729 is the only incorrect ratio code, test drive to see whether 6th gear actually engages and holds (OBD-Codes.com).
Inspect the transmission wiring and connectors you can reach for damage or corrosion (RepairPal lists wiring as a cause).

Typical fixes

Correct the fluid level, or change the automatic transmission fluid and filter, which RepairPal lists as the common repair
Repair any shift solenoid or wiring fault that has its own code (OBD-Codes.com, RepairPal)
Repair a blocked passage or failed valve body / main control (OBD-Codes.com, RepairPal)
Repair internal mechanical transmission damage (both sources)
Repair or reprogram a failed TCM or PCM, only after the transmission itself checks out (both sources list control modules)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The transmission slips, won't go into 6th gear or drops into limp mode
Several incorrect ratio codes are stored, which OBD-Codes.com says can point to an internal mechanical or fluid pressure problem
Diagnosis needs an advanced scan tool to compare the commanded gear and engine speed with transmission output speed, plus the factory service manual (OBD-Codes.com)
Repairs inside the transmission need advanced knowledge of transmission operation and overhaul (OBD-Codes.com)

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0729 serious?

It can be. RepairPal rates it Urgent, and OBD-Codes.com says it can come with slipping or a transmission that won't shift into 6th gear. Driving on a slipping transmission can make the damage worse, so get it checked soon.

Can low transmission fluid cause P0729?

Yes. Both sources list low or dirty transmission fluid as a cause, and RepairPal lists a fluid and filter change as the common repair. Check the fluid before anything else, but if the code comes back after correcting it, the problem is likely inside the transmission.

What's the difference between P0729 and P0730?

P0729 points specifically to 6th gear, while P0730 is the general incorrect gear ratio code. Codes P0731 to P0736 cover the other individual gears (OBD-Codes.com).

How much does it cost to fix P0729?

Neither source gives a repair cost. It can range from a fluid service to valve body or internal transmission repair, so get a diagnosis or a written estimate before replacing parts.

Sources

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.