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DTC codes / P25xx · Vehicle speed, idle control and auxiliary inputs / P2518

P2518A/C Refrigerant Pressure Sensor 'B' Circuit High

P2518 indicates that the powertrain control module (PCM) has detected an abnormally high voltage on the signal circuit for the 'B' refrigerant pressure sensor, which is typically the high-side pressure sensor in the air conditioning system. The PCM interprets this high voltage as a pressure reading that is out of range, often because the sensor circuit is open, shorted to voltage, or the sensor itself has failed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The air conditioning compressor may not engage, resulting in no cold air from the vents.
  • The climate control system may default to a fail-safe mode, such as running the blower only on high speed.
  • A warning light on the dashboard, often the check engine light or a specific A/C system indicator.
  • In some vehicles, the radiator cooling fan may run continuously as a precaution.
  • Often no symptoms besides the warning light, especially if the ambient temperature is low and the A/C is not in use.

Common causes, most likely first

  1. Open circuit or high resistance in the signal wire between the 'B' refrigerant pressure sensor and the PCM.
  2. Short to voltage on the signal circuit, which can be caused by chafed wiring or a faulty connection.
  3. Failed 'B' refrigerant pressure sensor, where the internal electronics produce a high voltage output.
  4. Corroded or loose electrical connector at the sensor or PCM, leading to intermittent high voltage readings.
  5. PCM internal fault, though this is less common and should be diagnosed last.
  6. Low refrigerant charge or overcharge can sometimes cause the sensor to read out of range, but usually sets a different code.
  7. Aftermarket accessories or improper wiring repairs that introduce voltage into the signal circuit.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the A/C and engine control systems.
  2. Inspect the 'B' refrigerant pressure sensor connector and wiring for damage, corrosion, or loose pins.
  3. Measure the sensor reference voltage and signal voltage with a digital multimeter, comparing to manufacturer specifications.
  4. Check the sensor's ground circuit for integrity, as a poor ground can cause high signal voltage.
  5. If the wiring and connectors are good, test the sensor with a known good unit or use a pressure gauge to compare actual refrigerant pressure to the sensor's reading.
  6. Repair or replace any faulty wiring, connectors, or the sensor as needed, then clear the code and verify the repair.
  7. If the code persists after all external checks, follow the manufacturer's diagnostic flow for PCM testing or replacement.

Don't overlook the ground circuit

  • A high voltage reading on the signal circuit can be caused by a poor ground at the sensor, which raises the reference voltage and tricks the PCM into seeing high pressure.
  • The 'B' sensor is often the high-side pressure sensor, but on some vehicles it may be the low-side or a second sensor in a dual-sensor system, so consult the specific wiring diagram.
  • This code can be set by a simple unplugged sensor, so always check that the connector is fully seated before condemning the sensor.
  • Incorrect refrigerant charge can cause the sensor to read out of range, but it typically sets a performance code rather than a circuit high code.
  • Aftermarket alarm or remote start installations that tap into sensor wiring are a hidden cause of voltage interference on the signal line.

Can I keep driving with P2518?

You can generally drive the vehicle with this code, but the air conditioning may not function, which could be uncomfortable in hot weather. Avoid using the A/C system until the fault is repaired to prevent potential compressor damage, and address the issue promptly to avoid secondary problems.

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.

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