AutoCodes – GMC – P0731 2018 GMC Sierra

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

Quick Answer

The transmission turbine speed sensor and vehicle speed sensor are hall-effect sensors. Common causes include Low transmission fluid level, Shift solenoid mechanical fault, Faulty Turbine Sensor. 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, Shift solenoid mechanical fault, Faulty Turbine Sensor.
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.

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Code Popularity 171

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 29, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0731 2018 GMC Sierra Description

The transmission turbine speed sensor and vehicle speed sensor are hall-effect sensors. The turbine speed sensor is mounted to the transmission housing and faces the reluctor attached to the 1-2-3-4-5-6 clutch piston housing. The vehicle speed sensor is mounted to the low and reverse clutch housing on 2WD, or transfer case rear case half on 4WD. The vehicle speed sensor faces a reluctor wheel attached to the transmission output shaft on 2WD, or a reluctor wheel attached to the transfer case rear output shaft on 4WD.
The TCM provides a 9 V reference circuit and a signal circuit to each of the sensors. As the 1-2-3-4-5-6 clutch piston housing and transmission output shaft or transfer case output rotates, the sensors produce a signal frequency based on the teeth on the reluctor wheel. The TCM calculates the transmission gear ratio based on the speed sensor signals and compares the calculated gear ratio to the commanded gear ratio.
The Diagnostic Trouble Code (DTC) will be set when the TCM detects the calculated gear ratio with 1st gear commanded differs from the known 1st gear ratio for 2 s.

OBDII Code P0731 2018 GMC Sierra - Transmission 1st Gear Ratio Incorrect - AutoCodes.com — P0731 2018 GMC Sierra Code - Transmission 1st Gear Ratio Incorrect

What does this mean?

What are the Possible Causes of the DTC P0731 2018 GMC Sierra?

Low transmission fluid level
Shift solenoid mechanical fault
Faulty Turbine Sensor
Faulty Output Speed Sensor

How to Fix the DTC P0731 2018 GMC Sierra?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0731 2018 GMC Sierra code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0731 2018 GMC Sierra code?

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Need Help with the Code?

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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.