Vehicle Safety
Recalls Search 320,000+ NHTSA safety recalls Complaints 2.1M+ consumer safety complaints TSBs 4.7M technical service bulletins VIN Lookup Decode any vehicle VIN instantly OBD Codes 12,000+ diagnostic trouble codes Fuel Economy EPA MPG data for all vehicles Safety Ratings 11,700+ NHTSA crash test ratings Investigations 5,300+ NHTSA defect investigations Statistics Recall trends & safety analysis
Consumer Safety
Product Safety 9,700+ CPSC product recalls Food Safety 28,600+ FDA food recalls Pet Safety 1.3M FDA animal adverse events Drug Safety 17,500+ FDA drug recalls Device Safety 38,400+ FDA device recalls Workplace Safety 102,900+ OSHA injury reports Brand History Cross-category recall lookup by company
Infrastructure
Bridge Safety 624,000 bridge inspections Aviation Safety 30,000+ NTSB aviation events Dam Safety 92,600 dam safety records Water Safety 433,000+ public water systems Railroad Safety 438,000+ rail crossings Pipeline Safety 8,800+ pipeline incidents State Safety Dashboards Safety grades for all 50 U.S. states ZIP Safety Report Check any 5-digit ZIP across 9 datasets
Public Health
Nursing Homes 14,700 CMS rated facilities Environmental 80,000+ hazardous sites & releases
Blog

Vehicle Safety

Vehicle Recalls320,000+ NHTSA safety recalls Browse VehiclesEvery make, model and year Complaints2.1M+ consumer safety complaints TSBs4.7M technical service bulletins VIN LookupDecode any vehicle VIN instantly OBD Codes12,000+ diagnostic trouble codes Fuel EconomyEPA MPG data for all vehicles Safety Ratings11,700+ NHTSA crash test ratings Investigations5,300+ NHTSA defect investigations StatisticsRecall trends & safety analysis Compare VehiclesTwo vehicles side by side

Consumer Safety

Product Safety9,700+ CPSC product recalls Food Safety28,600+ FDA food recalls Pet Safety1.3M FDA animal adverse events Drug Safety17,500+ FDA drug recalls Device Safety38,400+ FDA device recalls Workplace Safety102,900+ OSHA injury reports Brand HistoryRecall lookup by company

Infrastructure

Bridge Safety624,000 bridge inspections Aviation Safety30,000+ NTSB aviation events Dam Safety92,600 dam safety records Water Safety433,000+ public water systems Railroad Safety438,000+ rail crossings Pipeline Safety8,800+ pipeline incidents State DashboardsSafety grades for all 50 states ZIP ReportAny 5-digit ZIP across 9 datasets

Public Health

Nursing Homes14,700 CMS rated facilities Environmental80,000+ hazardous sites & releases BlogGuides, news & safety insights

OBD Code P0646

A/C Clutch Relay Control Circuit Low

CodeP0646
DescriptionA/C Clutch Relay Control Circuit Low
Possible CausesShort to ground|Faulty relay
SymptomsA/C compressor won't activate
SystemComputer

What Does P0646 Mean?

A/C Clutch Relay Control Circuit Low. This diagnostic trouble code (DTC) is stored when the vehicle's onboard computer detects an issue with the computer.

Code Breakdown

P = Powertrain code

0 = Generic (SAE standard)

How to Fix P0646

Follow these diagnostic steps to identify and resolve the issue. Always start with the simplest checks before moving to more involved repairs.

  1. Check refrigerant level — low charge is the most common A/C issue.
  2. Inspect the A/C compressor clutch for engagement when the system is turned on.
  3. Check the A/C pressure sensor and high/low pressure switch.
  4. Inspect the compressor connector and wiring.
  5. Check for refrigerant leaks using a UV dye or electronic leak detector.
  6. If the compressor is seized or noisy, replacement is needed along with a system flush.
  7. Recharge the system with the correct refrigerant type and amount, then clear codes.

Note: These are general diagnostic guidelines. Some vehicles may have model-specific procedures. Always consult your vehicle's service manual for exact specifications and torque values. If you are not comfortable performing these steps, visit a qualified mechanic.

Frequently Asked Questions

Is P0646 serious?

The severity depends on the underlying cause. Some triggers for P0646 are minor (like a loose gas cap), while others may indicate a more significant problem. We recommend having the code diagnosed with a proper scan tool to determine the exact cause before deciding on urgency.

Can I clear P0646 myself?

You can clear any OBD-II code with a code scanner or by disconnecting the battery for 15-30 minutes. However, clearing the code without fixing the underlying problem will cause it to return, usually within one or two drive cycles. If the code triggered the check engine light, the light will come back on. Fix the root cause first, then clear the code.

How much does it cost to fix P0646?

Repair costs vary widely depending on the root cause. Some fixes are free (like tightening a gas cap) while others can cost several hundred dollars (like replacing a catalytic converter or oxygen sensor). A proper diagnosis with a professional scan tool, not just reading the code, is the first step to getting an accurate repair estimate. Many auto parts stores offer free code reading, but a thorough diagnosis usually requires a mechanic.

View All OBD Codes