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P0731 2018 GMC Sierra Code - Transmission 1st Gear Ratio Incorrect

Quick Answer

The P0731 diagnostic trouble code (DTC) for a 2018 GMC Sierra indicates that the transmission is detecting an incorrect gear ratio in the first gear. Common causes include Low transmission fluid level or dirty transmission fluid, Faulty transmission solenoid, Worn-out clutch components. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0731 2018 GMC Sierra indicates Transmission 1st Gear Ratio Incorrect.
Common causes
Common causes include Low transmission fluid level or dirty transmission fluid, Faulty transmission solenoid, Worn-out clutch components.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 19, 2024
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Code P0731 2018 GMC Sierra Description

The P0731 diagnostic trouble code (DTC) for a 2018 GMC Sierra indicates that the transmission is detecting an incorrect gear ratio in the first gear. This means that the transmission is not shifting properly into first gear, which can lead to various performance issues. When the transmission fails to engage the correct gear ratio, it can result in poor acceleration, reduced fuel efficiency, harsh shifting, and even transmission slipping. This issue can also cause the transmission to overheat, leading to further damage if not addressed promptly.

OBDII Code P0731 2018 GMC Sierra - Transmission 1st Gear Ratio Incorrect
P0731 2018 GMC Sierra Code - Transmission 1st Gear Ratio Incorrect

Common Causes of P0731 2018 GMC Sierra

  1. Low transmission fluid level or dirty transmission fluid
  2. Faulty transmission solenoid
  3. Worn-out clutch components
  4. Malfunctioning transmission speed sensors
  5. Internal transmission damage or wear

Symptoms of P0731 2018 GMC Sierra

  1. Delayed or harsh shifting when accelerating
  2. Slipping or jerking movements when the vehicle is in first gear
  3. Reduced fuel efficiency
  4. Check Engine Light illuminated on the dashboard
  5. Transmission overheating

How to Fix P0731 2018 GMC Sierra

  1. Check and top up transmission fluid: Start by checking the transmission fluid level and condition. If the fluid is low or dirty, it should be topped up or replaced.
  2. Inspect and replace transmission solenoid: The transmission solenoid is responsible for shifting gears. If it is faulty, it may need to be replaced.
  3. Check and replace clutch components: Worn-out clutch components can cause gear ratio issues. Inspect and replace any damaged parts.
  4. Test and replace transmission speed sensors: Faulty speed sensors can lead to incorrect gear ratios. Test and replace as needed.
  5. Perform a transmission diagnostic: If the issue persists after the above steps, a comprehensive transmission diagnostic should be performed to identify any internal transmission problems that may require repair or replacement.

Cost to Fix P0731 2018 GMC Sierra

The cost of repairing the P0731 code for a 2018 GMC Sierra can vary depending on the specific cause of the issue. On average, the repair costs can range from $200 to $1000, including parts and labor. However, it is essential to note that the actual cost may be higher or lower based on factors such as the location of the repair shop, the vehicle's make and model, and the extent of the repairs needed. It is recommended to consult with a qualified mechanic or dealership to get an accurate estimate for the repair. Labor rates at auto repair shops typically range from $80 to $150 per hour, but rates may vary.

What does this mean?

Tech Notes for P0731 2018 GMC Sierra

Incorrect ratio Diagnostic Trouble Code (DTC) may indicate a component condition with piston seals, clutch plates, or solenoids or it may be caused by a faulty turbine or output speed sensor signal.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0731 2018 GMC Sierra Code

1. What does the OBDII code P0731 mean on a 2018 GMC Sierra?

P0731 indicates that the transmission control module has detected an incorrect gear ratio in 1st gear, which can be caused by mechanical or electrical issues.

2. What are the common symptoms of code P0731 in a 2018 GMC Sierra?

Symptoms include harsh shifting, slipping in 1st gear, decreased fuel efficiency, transmission overheating, and the check engine light turning on.

3. What are the possible causes of the P0731 code?

Possible causes include low transmission fluid, a faulty solenoid, worn transmission bands or clutches, a damaged torque converter, or issues with the transmission control module.

4. Can driving with a P0731 code damage my 2018 GMC Sierra?

Yes, driving with this code can lead to further transmission damage, reduced performance, and potential safety risks. It should be diagnosed and repaired promptly.

5. How do I troubleshoot the P0731 code on my GMC Sierra?

Start by checking the transmission fluid level and condition. If it’s low or dirty, refill or replace it. If the fluid is fine, inspect the solenoids, clutches, and wiring for damage or wear.

6. How much does it cost to fix the P0731 code on a 2018 GMC Sierra?

Repair costs vary depending on the issue. Simple fixes like fluid replacement may cost $100-$200, while transmission repairs or replacements can exceed $1,500.

7. Can a bad transmission solenoid cause the P0731 code?

Yes, a malfunctioning solenoid can affect gear engagement and lead to an incorrect gear ratio, triggering the P0731 code.

8. How can I prevent the P0731 code from occurring again?

Regularly check and maintain the transmission fluid, follow the manufacturer’s maintenance schedule, and address transmission issues promptly to prevent further damage.

9. Will resetting the check engine light fix the P0731 code?

No, resetting the light won’t fix the underlying issue. The root cause of the incorrect gear ratio needs to be diagnosed and repaired.

10. Is a P0731 code specific to the 2018 GMC Sierra?

No, the P0731 code is a generic OBDII code and can appear on other vehicles, but the specific causes and symptoms may vary depending on the make and model.

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