AutoCodes – Generic – P0646

P0646 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 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 24,279

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
Comments
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Code P0646 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 - Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage - AutoCodes.com — P0646 Code - Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P0646?

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?

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 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 code?

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Information for Specific Makes

P0646 BMW — Air Conditioning Clutch Relay Circuit Low
P0646 Buick — Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage
P0646 Cadillac — Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage
P0646 Chevrolet — Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage
P0646 Chrysler — Low Voltage Detected At The AC Clutch Relay
P0646 Dodge — Low Voltage Detected At The AC Clutch Relay
P0646 GMC — Air Conditioning Compressor Clutch Relay Control Circuit Low Voltage
P0646 Hyundai — Air Conditioning Clutch Relay Circuit Low
P0646 Jeep — Low Voltage Detected At The AC Clutch Relay
P0646 KIA — Air Conditioning Clutch Relay Circuit Low
P0646 Mazda — Air Conditioning Clutch Relay Circuit Low
P0646 MINI — Air Conditioning Clutch Relay Circuit Low
P0646 Suzuki — Air Conditioning Clutch Relay Circuit Low

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.