P1598
A/C Pressure Sensor Voltage Too High.
- Pontiac
- Powertrain
- Manufacturer code
- Low severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 5
- AreaVehicle speed, idle control and auxiliary inputs
- 98
- FaultThe specific fault in that area
What it means
P1598 on a Pontiac means the engine control unit has seen the signal voltage from the air conditioning refrigerant pressure sensor sitting higher than the expected range. This can be caused by a genuine over-pressure in the A/C system, or by a sensor, wiring or reference voltage fault that pushes the signal towards 5 volts. The exact trigger voltage and sensor location vary by model and engine, so check the manufacturer data for the vehicle.
Symptoms
- A/C compressor not engaging or cutting out
- Warm air from the vents with the A/C switched on
- Check engine light illuminated
- Cooling fans running constantly or at high speed
- Slight change in idle speed when A/C is selected
Possible causes
- Faulty A/C pressure sensor reading highlikely
- Signal wire shorted to the sensor reference voltage supplylikely
- Damaged, corroded or loose sensor connector terminalslikely
- Genuinely high refrigerant pressure from overcharge, blocked condenser or poor condenser airflowpossible
- Faulty cooling fan operation causing excessive system pressurepossible
- Open circuit in the sensor ground wirepossible
- Fault inside the engine control unitrare
How to diagnose
- Read the stored codes and freeze frame data, and note whether other codes are present and under what conditions P1598 set
- Inspect the A/C pressure sensor connector and wiring for damage, corrosion, chafing and water ingress
- Check the condenser for blockage by debris and confirm the cooling fans operate correctly with the A/C on
- Connect A/C service gauges and compare the actual system pressure with the pressure sensor reading in live data
- Back-probe the sensor and check for the correct reference voltage, a good ground and a signal that changes with pressure, using the model wiring diagram
- Check the signal wire for a short to the reference or battery supply with the sensor unplugged
- If the sensor reads high against known good gauge pressure, replace it and recheck the live data
How to fix
- Replace the A/C pressure sensor if it reads incorrectly against measured pressure
- Repair or replace damaged wiring and clean or renew faulty connector terminals
- Correct the refrigerant charge by recovering and recharging to the specified quantity
- Clear a blocked condenser and repair any faulty cooling fan or its relay
- Repair a failed ground or reference circuit as found by testing
Can I keep driving?
Low severity
The car is normally safe to drive, but the A/C may be disabled by the control unit. If the pressure is genuinely high, avoid using the A/C until it has been checked.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.