Transmission Gear 1 Incorrect Ratio
P0731 indicates that the transmission control module (TCM) has detected an incorrect gear ratio for first gear. This means the output shaft speed does not match the expected ratio relative to the input shaft speed. It often points to internal transmission issues such as worn clutches, a stuck valve body, or low fluid pressure, but can also be caused by electrical faults or a faulty TCM.
01. Most Common Causes
- Low or contaminated transmission fluid
- Faulty shift solenoid or valve body
- Worn or damaged clutch packs in first gear
- Faulty transmission control module (TCM)
- Internal transmission mechanical failure
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifting
- Transmission slipping out of first gear
- Reduced fuel economy
- Vehicle may go into limp mode
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Check transmission fluid level and condition.
Step 3: Inspect wiring and connectors to transmission solenoids and sensors.
Step 4: Perform a transmission pressure test to identify hydraulic issues.
Step 5: If no external issues found, internal inspection or professional transmission service is needed.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with P0731 can cause further transmission damage and lead to complete failure. Have it diagnosed and repaired as soon as possible.
How much does it cost to fix?▼
Cost varies widely. A simple fluid change or solenoid replacement may cost $150-$400, while a full transmission rebuild can exceed $2,000. Diagnostic fees are typically $50-$150.