What does it mean?
P1599 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/C Pressure Sensor Circuit Low Input .
Symptoms
- Air conditioning does not switch on at all, because the module blocks the compressor at low pressure
- No cold air from the vents even on the coldest setting
- Compressor clutch never engages and there is no click when the button is pressed
- Check engine light on with the code stored
- Cooling fans do not come on for air conditioning demand
- Oily residue or refrigerant dye traces around pipe joints when there is a leak
Likely causes
- Signal wire shorted to ground where the harness has rubbed through
- Loss of the 5 V reference voltage, which often sets codes on other sensors at the same time
- Open circuit in the signal wire or a terminal pushed out of the connector
- Refrigerant charge too low because of a leak, so the sensor reports a genuinely low pressure
- Internally failed sensor giving no output
- Water and corrosion in the sensor connector bridging or breaking the contacts
- Faulty reference supply inside the control module
How to fix it
- Check whether other sensors sharing the same 5 V reference have also set codes, which points to a shared circuit fault
- Connect manifold gauges and compare the real static pressure with the value in live data
- Inspect the sensor connector for water, corrosion and pushed-back terminals
- With the ignition on, measure the reference voltage and the ground at the harness side of the connector
- Backprobe the signal wire and check whether it is being held at zero volts by a short to ground
- Leak test the refrigerant circuit and recharge to the correct weight if the system is low
- Replace the sensor once the wiring and refrigerant charge are proven correct, then verify the compressor engages