Transmission Gear 6 Incorrect Ratio
The P0729 code indicates that the powertrain control module (PCM) has detected an incorrect gear ratio when the transmission is commanded to shift into 6th gear. This typically means the actual gear ratio does not match the expected ratio for 6th gear, often due to internal transmission slippage, a stuck valve, or a faulty shift solenoid. The condition can lead to harsh shifting, reduced fuel economy, and potential transmission damage if ignored.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifting, especially into 6th gear
- Transmission slipping or shuddering
- Reduced fuel economy
- Transmission may go into limp mode
2. Most Common Causes
- Low, contaminated, or degraded transmission fluid
- Faulty or stuck shift solenoids (especially those controlling 6th gear clutches/brakes)
- Valve body with clogged passages, excessive wear, or failed separator plate
- Faulty, dirty, or damaged input speed sensor (ISS) or output speed sensor (OSS)
- Internal mechanical wear: slipping clutches, bands, planetary gears, or torque converter
- Internal TCM failure or need for software update/reprogramming
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Check transmission fluid level and condition; top off or replace if necessary.
Step 3: Inspect wiring and connectors to the transmission solenoids and TCM for damage or corrosion.
Step 4: Perform a transmission pressure test to identify internal leaks or solenoid issues.
Step 5: If no external issues found, remove transmission pan and inspect for debris; replace solenoids or valve body as needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with P0729, as it can cause further transmission damage. Short trips to a repair shop are acceptable, but avoid heavy acceleration or towing.
How much does it cost to fix?▼
Repair costs vary widely: a simple fluid change or solenoid replacement may cost $150-$400, while internal transmission rebuild or replacement can exceed $2,000.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.