01 P0021 A camshaft postion - timing over-advanced or system p… • 02 Mechanics Admit They're Surprised How Many Owners Don't Kno… • 03 Toyota Hilux Spare Parts List and Part Numbers • 04 What Is The Best Gear To Apply When Driving Downhill? • 05 How To Fix Automatic Transmission Not Shifting • 06 Car Security Systems: What They Are and How to Install Them • 07 How to Track Electrical Problems in Your Car with Clear Beg… • 08 Disc Brake Friction Mechanics and Heat Dissipation • 09 How Euro Standards Are Helping to Achieve Climate Change Go… • 10 Mechanics Shocked At How Many Cars Are Destroyed By Owners … •

DTC codes / P06xx · Computer and output circuits / P06A1

P06A1Variable A/C Compressor Control Circuit Low

P06A1 indicates that the powertrain control module (PCM) has detected an abnormally low voltage on the control circuit for the variable air conditioning (A/C) compressor. The PCM commands the compressor to stroke or change displacement via a control valve, and the circuit voltage is lower than expected, which can prevent proper A/C operation or trigger a fault.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The A/C may not blow cold air, or cooling performance may be inconsistent.
  • The A/C compressor clutch may not engage, or the compressor may run at a fixed displacement.
  • The check engine light (malfunction indicator lamp) is illuminated.
  • Often no symptoms besides the warning light, especially if the A/C system still functions adequately.
  • Possible electrical issues such as blown fuses or intermittent operation of the A/C compressor.
  • The climate control system may default to a fail-safe mode, reducing cooling or disabling A/C entirely.

Common causes, most likely first

  1. A short to ground or open circuit in the variable A/C compressor control circuit wiring.
  2. Faulty variable A/C compressor control solenoid or valve.
  3. Corroded, loose, or damaged electrical connector at the compressor or PCM.
  4. Blown fuse or faulty relay supplying power to the A/C compressor control circuit.
  5. Failed PCM driver for the A/C compressor control circuit (rare but possible).
  6. Aftermarket or damaged electrical accessories interfering with the circuit.
  7. Moisture intrusion or physical damage to the wiring harness.

How to diagnose and fix it

  1. Verify the code and check for any related A/C system codes using a scan tool.
  2. Inspect the A/C compressor control circuit wiring and connectors for damage, corrosion, or looseness.
  3. Check the fuse and relay associated with the A/C compressor control circuit and replace if necessary.
  4. Measure resistance and voltage on the control circuit to identify shorts or opens, comparing to manufacturer specifications.
  5. Test the variable A/C compressor control solenoid for proper resistance and operation; replace if faulty.
  6. If the circuit and solenoid are good, check the PCM output signal and wiring back to the PCM; repair as needed.
  7. Clear the code and verify the repair by running the A/C system and monitoring live data for the control circuit.

Before you replace the A/C compressor

  • A low voltage on the control circuit often results from a poor ground connection or a chafed wire, not a failed compressor, so always perform a thorough visual inspection first.
  • Some vehicles use a variable displacement compressor without a traditional clutch; the control valve receives a pulse-width modulated signal, and a low circuit voltage can cause the compressor to default to full stroke or no stroke.
  • The PCM may set P06A1 if the control circuit voltage is low only under certain conditions, such as when the A/C is commanded on, so intermittent faults can be missed during a quick check.
  • A weak battery or charging system issue can cause low voltage on multiple circuits, including the A/C control circuit, so check the vehicle's overall electrical health before condemning components.
  • Replacing the A/C compressor without diagnosing the control circuit can lead to repeat failures if the underlying wiring or connector issue is not corrected.

Can I keep driving with P06A1?

You can generally drive the vehicle with this code, but the A/C may not function properly, which could be uncomfortable in hot weather. Avoid using the A/C system until the fault is repaired to prevent potential further damage to the compressor or electrical components.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage