Transmission Gear 1 Incorrect Ratio
The P0731 code indicates that the powertrain control module (PCM) has detected an incorrect gear ratio for first gear. This typically means the transmission is slipping or not engaging properly, often due to low fluid, worn clutches, or a faulty solenoid. The PCM compares input and output shaft speeds to verify the ratio; if it deviates from the expected value, the code sets.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifting, especially from 1st to 2nd
- Transmission slipping or revving without acceleration
- Vehicle may go into limp mode or fail to move
2. Most Common Causes
- Low or contaminated transmission fluid (burnt or dirty)
- Faulty or stuck shift control solenoid (especially the one for first gear)
- Defective input or output speed sensor
- Electrical issues in the wiring or connectors of speed sensors or solenoids (short or open circuit)
- Internal mechanical transmission failure (bands, clutches, planetary gears, or valve body)
- Faulty transmission control module (TCM) or powertrain control module (PCM)
3. Step-by-Step Diagnosis
Step 1: Check transmission fluid level and condition; top off or replace if necessary.
Step 2: Scan for additional codes and perform a transmission pressure test.
Step 3: Inspect wiring and connectors to the transmission control module and solenoids.
Step 4: If fluid and electrical are OK, internal inspection or professional diagnosis is needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, driving with P0731 can cause further transmission damage. It's best to have it towed to a shop.
How much does it cost to fix?▼
Cost varies: fluid change $50-$150, solenoid replacement $150-$400, transmission rebuild $1500-$3500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.