AutoCodes – GMC – P0646 2018 GMC Sierra

P0646 2018 GMC Sierra Code - Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage

Quick Answer

When the Air Conditioning (A/C) switch is pressed, the Heating, Ventilation, and Air Conditioning (HVAC) control module sends an A/C request message to the Engine Control Module (ECM) via serial data. Common causes include Faulty Air Conditioning (A/C) Compressor Clutch Relay, Air Conditioning Compressor Clutch Relay harness is open or shorted, Air Conditioning Compressor Clutch Relay circuit poor electrical connection. Severity is Low - monitor the vehicle and repair when practical. The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

What it means: P0646 2018 GMC Sierra indicates Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage.
Common causes: Common causes include Faulty Air Conditioning (A/C) Compressor Clutch Relay, Air Conditioning Compressor Clutch Relay harness is open or shorted, Air Conditioning Compressor Clutch Relay circuit poor electrical connection.
Severity: Low - monitor the vehicle and repair when practical.
Can I drive?: The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

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Code Popularity 222

How popular is this code, among other codes? Low

Repair Importance Level

Low (Monitor) (1 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 17, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0646 2018 GMC Sierra Description

When the Air Conditioning (A/C) switch is pressed, the Heating, Ventilation, and Air Conditioning (HVAC) control module sends an A/C request message to the Engine Control Module (ECM) via serial data. The ECM then grounds the A/C compressor clutch relay coil control circuit, closing the relay contacts. The closed relay contacts provide voltage to the compressor clutch causing it to engage. The Diagnostic Trouble Code (DTC) will be set when the ECM detects a short to ground or an open at the A/C compressor clutch relay control circuit.

OBDII Code P0646 2018 GMC Sierra - Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage - AutoCodes.com — P0646 2018 GMC Sierra Code - Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P0646 2018 GMC Sierra?

Faulty Air Conditioning (A/C) Compressor Clutch Relay
Air Conditioning Compressor Clutch Relay harness is open or shorted
Air Conditioning Compressor Clutch Relay circuit poor electrical connection
Faulty Air Conditioning Compressor Clutch
Faulty Engine Control Module (ECM)

How to Fix the DTC P0646 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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0646 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 P0646 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 P0646 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P0646 in a 2018 GMC Sierra related to the Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage?

The common symptoms include intermittent or total loss of air conditioning, illuminated AC warning light on the dashboard, and potential engine overheating due to the AC compressor not engaging.

2. What are the possible causes of OBDII code P0646 in a 2018 GMC Sierra indicating a low voltage issue in the Air Conditioning Compressor Clutch Relay Control Circuit?

Possible causes include a faulty air conditioning compressor clutch relay, damaged wiring or connectors in the relay circuit, low refrigerant levels, or a malfunctioning AC compressor clutch.

3. How can I diagnose the issue causing OBDII code P0646 in my 2018 GMC Sierra related to the Air Conditioning Compressor Clutch Relay Control Circuit?

Diagnose the problem by checking the AC compressor clutch relay for proper function, inspecting the relay circuit for any damage, verifying refrigerant levels, and testing the AC compressor clutch for proper engagement.

4. Can I drive my 2018 GMC Sierra with OBDII code P0646 related to the Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage?

It is not recommended to drive the vehicle with this issue as it may lead to further damage to the air conditioning system and potential engine overheating due to the AC compressor not functioning properly.

5. How can I repair OBDII code P0646 in my 2018 GMC Sierra indicating a low voltage problem in the Air Conditioning Compressor Clutch Relay Control Circuit?

Repair the issue by replacing the faulty air conditioning compressor clutch relay, repairing any damaged wiring or connectors in the relay circuit, ensuring proper refrigerant levels, and addressing any problems with the AC compressor clutch.

6. Is it safe to reset the OBDII code P0646 in my 2018 GMC Sierra related to the Air Conditioning Compressor Clutch Relay Control Circuit?

While you can reset the code to clear the warning light temporarily, it is crucial to address the underlying issue causing the low voltage problem in the air conditioning system to prevent further damage and ensure proper functionality.

7. Can a DIY enthusiast fix OBDII code P0646 in a 2018 GMC Sierra indicating a low voltage issue in the Air Conditioning Compressor Clutch Relay Control Circuit?

A DIY enthusiast with automotive repair experience may be able to address the issue by following diagnostic procedures, replacing components like the relay, and ensuring proper repairs are made to the air conditioning system.

8. What are the potential risks of ignoring OBDII code P0646 in a 2018 GMC Sierra related to the Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage?

Ignoring the code can lead to continued loss of air conditioning function, potential damage to the AC compressor, increased engine heat due to the compressor not engaging, and overall discomfort while driving in hot weather.

9. How long does it typically take to repair OBDII code P0646 in a 2018 GMC Sierra related to the Air Conditioning Compressor Clutch Relay Control Circuit?

The repair time can vary based on the exact cause of the issue, but typically, it may take a few hours to a half-day for a professional mechanic to diagnose, repair, and test the air conditioning system to resolve the problem.

10. Are there any preventive maintenance tips to avoid encountering OBDII code P0646 in a 2018 GMC Sierra indicating a low voltage issue in the Air Conditioning Compressor Clutch Relay Control Circuit?

Regularly inspecting and servicing the air conditioning system, checking refrigerant levels, ensuring proper relay function, and addressing any minor issues promptly can help prevent the occurrence of this code and maintain optimal AC performance in your GMC Sierra.