AutoCodes – GMC – P0121 2017 GMC Sierra

P0121 2017 GMC Sierra Code - Throttle Position Sensor 1 Performance

Quick Answer

The Throttle Body Assembly contains a contact-less inductive throttle position sensing element that is managed by a customized integrated circuit. Common causes include Faulty Throttle Body Assembly, Throttle Body Assembly harness is open or shorted, Throttle Body Assembly circuit poor electrical connection. 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: P0121 2017 GMC Sierra indicates Throttle Position Sensor 1 Performance.
Common causes: Common causes include Faulty Throttle Body Assembly, Throttle Body Assembly harness is open or shorted, Throttle Body Assembly circuit poor electrical connection.
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 333

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 20, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
FAQs
Comments
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Code P0121 2017 GMC Sierra Description

The Throttle Body Assembly contains a contact-less inductive throttle position sensing element that is managed by a customized integrated circuit. The throttle position sensor is mounted within the throttle body assembly and is not serviceable. The Engine Control Module (ECM) supplies the throttle body with a 5 V reference circuit, a low reference circuit. The asynchronous signal means communication is only going from the throttle body to the ECM. The throttle body cannot receive data from the ECM over the signal/serial data circuit. The throttle position sensor provides a signal voltage that changes relative to throttle blade angle. The throttle position sensor information is transmitted between the throttle body and the ECM on the signal/serial data circuit. The ECM decodes the serial data signal and is used as voltages for throttle position sensor 1 and 2. The Diagnostic Trouble Code (DTC) will be set when the ECM detects that the throttle position sensor 1 voltage is stuck in range for greater than 1 s.

OBDII Code P0121 2017 GMC Sierra - Throttle Position Sensor 1 Performance - AutoCodes.com — P0121 2017 GMC Sierra Code - Throttle Position Sensor 1 Performance

What does this mean?

What are the Possible Causes of the DTC P0121 2017 GMC Sierra?

Faulty Throttle Body Assembly
Throttle Body Assembly harness is open or shorted
Throttle Body Assembly circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0121 2017 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

User Submitted Video

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0121 2017 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.

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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 P0121 2017 GMC Sierra Code

What does the OBDII code P0121 mean on a 2017 GMC Sierra?

P0121 indicates an issue with the performance of Throttle Position Sensor 1, where its signal is inconsistent or outside the expected range compared to other sensors.

What are the common symptoms of P0121 on a 2017 GMC Sierra?

Symptoms may include poor acceleration, rough idling, hesitation, reduced engine power (limp mode), and the check engine light turning on.

What causes the P0121 code on a 2017 GMC Sierra?

Common causes include a faulty throttle position sensor (TPS), wiring or connector issues, carbon buildup in the throttle body, or problems with the engine control module (ECM).

Can I drive my 2017 GMC Sierra with the P0121 code?

It is not recommended to drive with this code, as it can lead to reduced performance, unsafe driving conditions, or further damage to the engine and throttle system.

How do I diagnose the P0121 code on a 2017 GMC Sierra?

Start by checking the throttle position sensor and its wiring for damage or corrosion. Use a scan tool to monitor TPS data and compare it with the expected range.

How can I fix the P0121 code on my 2017 GMC Sierra?

Repairs may involve cleaning or replacing the throttle position sensor, repairing damaged wiring or connectors, cleaning the throttle body, or updating/replacing the ECM if necessary.

What tools do I need to fix the P0121 code on a 2017 GMC Sierra?

You may need a scan tool, multimeter, throttle body cleaner, and basic hand tools to perform diagnostics and repairs.

How much does it cost to repair the P0121 code on a 2017 GMC Sierra?

The cost can vary depending on the issue, ranging from $100-$300 for a throttle position sensor replacement or wiring repair, to higher costs if the ECM needs replacement.

Does a dirty throttle body cause the P0121 code on a 2017 GMC Sierra?

Yes, excessive carbon buildup in the throttle body can cause the TPS to send incorrect readings, triggering the P0121 code.

Will clearing the P0121 code fix the issue on a 2017 GMC Sierra?

Clearing the code without addressing the underlying issue will not resolve the problem, and the code is likely to return. Proper diagnostics and repairs are necessary.