Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means there's a problem with the part of the car's heating and cooling system that controls the flow of refrigerant. It's like a valve that isn't opening or closing properly, which can affect how well the car heats or cools the inside.
The P1D99 code indicates an issue with the control circuit of the heat pump expansion valve 'C'. This could be due to an open circuit, which means there's a break in the electrical path that should control the valve.
The heat pump expansion valve 'C' is responsible for regulating the flow of refrigerant in the vehicle's HVAC system. An open circuit in its control path can prevent it from functioning correctly, leading to inefficient heating or cooling.
• Poor heating or cooling performance
• HVAC system not responding
• Check engine light on
• Faulty expansion valve
• Damaged wiring or connectors
• Failed control module
HVAC: Heating, Ventilation, and Air Conditioning
Refrigerant: A substance used in the cooling cycle of air conditioning systems
• Check for any loose or damaged wiring to the expansion valve.
• Test the expansion valve for proper operation.
• Inspect the control module for faults.
• Repair or replace damaged wiring.
• Replace the faulty expansion valve.
• Reprogram or replace the control module if necessary.
• Multimeter
• OBD-II scanner
• Screwdriver set
$150 - $500
Moderate
• Vehicle 1
• Vehicle 2
• Vehicle 3
• Regular maintenance of the HVAC system
• Inspect wiring for wear and tear
• Ensure proper refrigerant levels
Sensor Issue
• Have the HVAC system checked regularly.
• Address any HVAC issues promptly to avoid discomfort.
• Consult a professional if the check engine light is on.
Check with your vehicle manufacturer for warranty coverage on HVAC components.
This code has been associated with vehicles that have complex HVAC systems, particularly in hybrid and electric vehicles.
Moderate – Addressing this issue will improve comfort and prevent further HVAC system issues.
Driving with a malfunctioning HVAC system can lead to discomfort and potential safety issues due to fogged windows.
• Vehicle at operating temperature
• HVAC system activated
The expansion valve is typically located in the HVAC system, near the evaporator core.
Q: What happens if I ignore this code?
A: Ignoring this code can lead to poor heating or cooling performance and potential damage to the HVAC system.
Q: Can I fix this issue myself?
A: If you're experienced with car repairs, you might be able to fix wiring issues. However, replacing components should be done by a professional.
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Network faults often require full-system access instead of a generic code reader alone.
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Relevant when EVAP diagnosis points toward purge-flow or purge-control faults.
EVAP diagnosis often includes purge-flow and valve-control faults.
Confirm the failed valve and exact fitment before buying parts.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.