AutoCodes – GMC – P0645 2015 GMC Sierra

P0645 2015 GMC Sierra Code - Air Conditioning Compressor Clutch Relay Control Circuit

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 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: P0645 2015 GMC Sierra indicates Air Conditioning Compressor Clutch Relay Control Circuit.
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: 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 224

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 17, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code P0645 2015 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 P0645 2015 GMC Sierra - Air Conditioning Compressor Clutch Relay Control Circuit - AutoCodes.com — P0645 2015 GMC Sierra Code - Air Conditioning Compressor Clutch Relay Control Circuit

What does this mean?

What are the Possible Causes of the DTC P0645 2015 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 P0645 2015 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 P0645 2015 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 P0645 2015 GMC Sierra code?

Need more information on how to fix the P0645 2015 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0645 2015 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 P0645 2015 GMC Sierra Code

1. What does the OBDII code P0645 mean on a 2015 GMC Sierra?

P0645 indicates a problem with the Air Conditioning (A/C) Compressor Clutch Relay Control Circuit, which may prevent the A/C system from functioning properly.

2. What are the symptoms of a P0645 code?

Common symptoms include the A/C not blowing cold air, the compressor not engaging, and the check engine light or A/C system warning light being illuminated.

3. What causes the P0645 code on a 2015 GMC Sierra?

Potential causes include a faulty A/C compressor clutch relay, damaged wiring or connectors in the control circuit, a blown fuse, or a failing A/C control module.

4. Can I still drive my 2015 GMC Sierra with a P0645 code?

Yes, the vehicle is typically drivable, but the A/C system may not function, especially in hot weather. Prolonged use without repair could cause further electrical issues.

5. How is the P0645 code diagnosed?

A mechanic will use a scan tool to confirm the code, inspect the A/C relay and wiring for damage, check the fuses, and test the A/C clutch relay for proper operation.

6. How do you fix a P0645 code on a 2015 GMC Sierra?

Repairs may include replacing the A/C compressor clutch relay, repairing or replacing damaged wiring or connectors, or replacing the A/C control module if it is faulty.

7. What tools are needed to fix a P0645 code?

Tools may include a scan tool, multimeter, wiring diagram, and basic hand tools for inspecting and replacing components in the A/C control circuit.

8. How much does it cost to fix a P0645 code?

Repair costs can range from $50 to $300 depending on whether the issue is with the relay, wiring, or the A/C control module.

9. Can a blown fuse cause the P0645 code?

Yes, a blown fuse in the A/C compressor clutch relay circuit can trigger the P0645 code and prevent the A/C system from working.

10. Will clearing the P0645 code fix the problem?

Clearing the code with a scan tool may temporarily turn off the check engine light, but the underlying problem must be addressed to prevent the code from returning.