AutoCodes – GMC – P0734 GMC

P0734 GMC Code - Transmission 4th 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: P0734 GMC indicates Transmission 4th 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 463

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
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
Comments
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Code P0734 GMC 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 4th gear commanded differs from the known 6th gear ratio for 2 s.

OBDII Code P0734 GMC - Transmission 4th Gear Ratio Incorrect - AutoCodes.com — P0734 GMC Code - Transmission 4th Gear Ratio Incorrect

What does this mean?

What are the Possible Causes of the DTC P0734 GMC?

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

How to Fix the DTC P0734 GMC?

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 P0734 GMC 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 P0734 GMC code?

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Information for Specific GMC Models

P0734 2014 GMC Sierra — Transmission 4th Gear Ratio Incorrect
P0734 2015 GMC Sierra — Transmission 4th Gear Ratio Incorrect
P0734 2016 GMC Sierra — Transmission 4th Gear Ratio Incorrect
P0734 2017 GMC Sierra — Transmission 4th Gear Ratio Incorrect
P0734 2018 GMC Sierra — Transmission 4th Gear Ratio Incorrect

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.