P0733 Code: Complete Guide to Gear 3 Incorrect Ratio
Everything you need to know about symptoms, diagnosis, repairs, and prevention
Understanding the P0733 Code
The P0733 code is a transmission-related diagnostic trouble code (DTC) that indicates an “Incorrect Gear Ratio” specifically for third gear. This means your vehicle’s Powertrain Control Module (PCM) has detected that the actual gear ratio in third gear does not match the expected ratio programmed in the vehicle’s computer system.
What is Gear Ratio?
Gear ratio refers to the relationship between the rotational speeds of two or more interlocking gears. In your transmission, it’s the ratio between the input shaft speed (from the engine) and the output shaft speed (to the wheels). The PCM calculates this ratio by comparing data from the input speed sensor (ISS) and output speed sensor (OSS).
How the P0733 Code is Triggered
The P0733 code is set when the PCM detects that the actual gear ratio in third gear does not match the expected ratio for more than a predetermined amount of time (usually 4-7 seconds).
The PCM continuously monitors and calculates the gear ratio by comparing input from:
- Input speed sensor (ISS) – measures transmission input shaft RPM
- Output speed sensor (OSS) – measures transmission output shaft RPM
- Transmission gear position – which gear the transmission is commanded to be in
When the vehicle is in third gear, the PCM expects a specific ratio between the ISS and OSS. If the calculated ratio deviates from the expected ratio beyond a certain threshold, the PCM interprets this as a problem and:
- Illuminates the Check Engine Light
- Stores the P0733 code in memory
- May put the transmission in “limp mode” (default to a single gear)
- May disable overdrive to prevent further damage
- Causes harsh shifting as the PCM attempts to compensate
Symptoms of P0733 Code
When a vehicle has a P0733 code, you may experience one or more of the following symptoms. The severity often depends on the underlying cause:
| Symptom | Description | Frequency | Urgency |
|---|---|---|---|
| Check Engine Light | Illumination of the check engine light on your dashboard | Very Common | MediumShould be addressed within a week |
| Transmission Slipping | Engine RPM increases without corresponding vehicle speed increase in 3rd gear | Common | HighShould be addressed immediately |
| Harsh Shifting | Rough or jarring shifts when transitioning to or from 3rd gear | Common | MediumShould be addressed within a week |
| No Third Gear | Transmission skips 3rd gear entirely or won’t engage it | Less Common | HighShould be addressed immediately |
| Poor Acceleration | Reduced power, especially when accelerating in 3rd gear | Common | MediumShould be addressed within a week |
| Unusual Noises | Whining, grinding, or clunking sounds from transmission | Less Common | HighShould be addressed immediately |
| Overheating | Transmission overheating, especially during highway driving | Occasional | HighShould be addressed immediately |
Common Causes of P0733 Code
The P0733 code can be caused by various issues within the transmission system. Here are the most common causes categorized by system component:
Technical Insight
In many automatic transmissions, third gear is typically a direct drive (1:1 ratio) where the input and output shafts rotate at the same speed. When the PCM detects that the ratio between the input and output speed sensors is not approximately 1:1 while in third gear, it triggers the P0733 code.
Comprehensive Diagnostic Procedure
Diagnosing a P0733 code requires a systematic approach. Follow these detailed steps for proper diagnosis:
Initial Scan and Code Verification
Use an advanced OBD-II scanner to confirm the P0733 code and check for any additional codes that might provide more clues. Record all codes and freeze frame data. Clear the codes and perform a test drive to see if the code returns, which confirms an active issue.
Comprehensive Transmission Fluid Inspection
Check the transmission fluid level with the engine running and transmission at operating temperature. Inspect the fluid’s condition, color, and smell. Healthy fluid should be red or reddish-brown and have a slightly sweet smell. Dark, burnt-smelling fluid indicates overheating, while milky fluid suggests coolant contamination.
Road Test with Live Data Monitoring
Perform a test drive with a scan tool connected to monitor input and output speed sensor data, especially during third gear operation. Pay attention to:
- Actual vs. commanded gear state
- Transmission fluid temperature
- Shift solenoid states
- Torque converter clutch operation
Speed Sensor Testing
Test both input and output speed sensors for proper operation:
- Check sensor resistance (typically 200-1500 ohms, refer to manufacturer specs)
- Inspect sensor wiring for damage, chafing, or corrosion
- Verify sensor mounting and air gap (if applicable)
- Check for proper AC voltage output while rotating the sensor target
Solenoid and Electrical Testing
Test the shift solenoids responsible for third gear operation:
- Check solenoid resistance (typically 20-30 ohms for most)
- Perform actuation test with scan tool if supported
- Inspect wiring and connectors for damage or corrosion
- Check for proper voltage and ground circuits
Transmission Pressure Tests
Connect a transmission pressure gauge to measure line pressure in various gears, especially third gear. Compare readings to manufacturer specifications. Low pressure may indicate:
- Worn pump
- Internal leaks
- Clogged filter
- Faulty pressure regulator
Advanced Diagnostics
If the cause remains elusive, consider:
- Transmission fluid pressure switch testing
- Valve body inspection for stuck valves or contamination
- Transmission adaptive learning reset and reprogramming
- Complete transmission tear-down and inspection
Repair Costs & Options for P0733 Code
The cost to repair a P0733 code can vary significantly depending on the root cause, your vehicle’s make and model, and your location. Below are estimated cost ranges for common repairs:
Transmission Fluid Service
Includes fluid and filter change
Best for: Early detection with minor issues
Speed Sensor Replacement
Parts and labor for one sensor
Best for: Faulty sensor diagnosis
Shift Solenoid Replacement
Parts and labor
Best for: Electrical issues only
Valve Body Repair
Repair or replacement
Best for: Internal hydraulic issues
Transmission Rebuild
Complete overhaul
Best for: Severe mechanical damage
Transmission Replacement
New or remanufactured unit
Best for: Non-repairable damage
Cost-Saving Tips
- Get multiple quotes from different repair shops
- Consider independent transmission specialists vs. dealerships
- Ask about remanufactured vs. new transmission options
- Check if your vehicle is still under warranty
- Consider extended warranty coverage if available
Note: These are estimated costs and can vary based on your location, vehicle make/model, and shop rates. Luxury and performance vehicles typically have higher repair costs.
Prevention & Maintenance Tips
To help prevent P0733 and other transmission issues, follow these maintenance tips and best practices:
- Transmission fluid and filter change: Every 30,000-60,000 miles (check your owner’s manual)
- Transmission inspection: At every oil change or at least annually
- Transmission flush: Only if recommended by your vehicle manufacturer
