A/C Refrigerant Pressure Sensor "A" Circuit High

What it means

The A/C refrigerant pressure sensor signal voltage is above the normal range. The A/C refrigerant pressure sensor measures refrigerant pressure so the ECU can protect the compressor and control the cooling fans. A high signal is usually caused by an open circuit (unplugged, broken wire), a missing ground or a short to voltage.

Symptoms

• Check engine light on
• Air conditioning not cooling or compressor not engaging
• Cooling fans running constantly

Probable causes

Most likely first

1. 1Open sensor ground wire
2. 2Signal wire shorted to the 5V reference or to battery voltage
3. 3Corroded connector terminals
4. 4Failed sensor

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Inspect the A/C refrigerant pressure sensor connector and wiring (on the high-pressure A/C line, usually near the condenser at the front of the car). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
3. 3Watch the A/C refrigerant pressure sensor reading on live data. With the engine off, the pressure reading should match the static pressure on a gauge set at that air temperature.
4. 4With the key on and the sensor unplugged, check for about 5 volts on the reference wire and a good ground (under 0.1 V drop) on the ground wire. Back-probe the signal wire with the sensor connected and watch the voltage change smoothly.
5. 5If the wiring checks out, test the sensor itself against the specification in a service manual.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair the damaged wiring or connector
• Replace the A/C refrigerant pressure sensor
• Clear the code and test drive to confirm the repair