Technical Description of OBD-II Trouble Code
The circuit for the A/C refrigerant pressure sensor B is registering a high reading.
What does that signify?
This is a standard diagnostic trouble code (DTC) that is typically applicable to OBD-II vehicles. It can be found in various vehicle makes such as Chevrolet / Chevy, Ford, Volvo, Dodge, Hyundai, Vauxhall, Honda, Nissan, Renault, Alfa Romeo, etc.
The A/C refrigerant pressure sensor plays a role in helping the HVAC (Heating, Ventilation and Air Conditioning) system maintain the desired temperature inside the vehicle.
The sensor is monitored by either the BCM (Body Control Module) or the ECC (Electronic Climate Control) Module to determine the system pressures and engage/disengage the compressor accordingly.
The A/C refrigerant pressure sensor is a pressure transducer that converts the pressure of the refrigerant system into an analog electrical signal. This allows the vehicle’s modules to monitor the pressure. Typically, it uses 3 wires: a 5 volt reference wire, a signal wire, and a ground wire. The modules compare the values of the signal wire to the 5 volt reference and can calculate the system pressures instantly.
The ECM (Engine Control Module) triggers the MIL (Malfunction Indicator Lamp) and displays the codes P2518 and associated codes (P2515, P2516, P2517, and P2518) when it detects a fault in the A/C refrigerant pressure sensor or its circuits. Before attempting any diagnosis or repair work on the A/C system, it is important to be aware of the potential hazards associated with working with pressurized refrigerant. In many cases, this type of code can be diagnosed without opening the refrigerant system.
The code P2518 A/C Refrigerant Pressure Sensor B Circuit High is set when one of the modules detects a high electrical value in the A/C refrigerant pressure sensor B or its circuit. An example of an A/C refrigerant pressure sensor:
What is the severity of this DTC?
In my opinion, the severity of any HVAC-related code is generally low. However, in this case, since pressurized refrigerant is involved, it may be a more urgent issue. There is a possibility that a refrigerant leak is causing this code, and leaking refrigerant can be hazardous. Therefore, it is important to have basic knowledge of refrigerant safety before attempting any repairs on the A/C system.
What are some of the symptoms of the code?
Symptoms of a P2518 diagnostic code may include:
What are some of the common causes of the code?
The causes of this P2518 transmission code may include:
What are some P2518 diagnostic and troubleshooting steps?
Prior to starting the troubleshooting process for any malfunction, it is recommended to research the Technical Service Bulletins (TSB’s) specific to the vehicle’s year, model, and transmission. This step can save time and money during diagnosis and repair!
Basic Step #1
Depending on the tools and knowledge available, you can easily verify the operation of the A/C refrigerant pressure sensors. There are two easy ways to do this: 1. Depending on the capabilities and limitations of your OBD reader/scan tool, you may be able to monitor refrigerant pressures and other desired values while the system is operating to verify the functionality of the sensor. 2. If you have an A/C manifold gauge set, you can mechanically monitor the pressures and compare them with the manufacturer’s specified values.
TIP: If you have no experience with refrigerant, it is not recommended to perform pressure testing. Make sure you have the necessary knowledge and expertise, as refrigerant is hazardous to the environment.
Basic Step #2
Test the A/C refrigerant pressure sensor. As mentioned earlier, in most cases, this sensor is a 3-wire pressure transducer. Therefore, testing it will involve testing between the pins and recording the findings. The desired values for this test can vary significantly depending on the manufacturer, temperatures, type of sensor, etc., so ensure that you have accurate information.
NOTE: When testing pins/connectors, make sure to use the appropriate test pins along with your multimeter. A damaged pin or connector could cause future intermittent electrical issues that are difficult to diagnose.
Basic Step #3
Check the wiring. Sometimes, these sensors are mounted on an A/C pressure line or close to a line connection, so the harness will be routed accordingly. I have personally seen these sensors get damaged by moving parts under the hood because the line was not secured properly. Make sure the sensor is physically intact and the line is securely fastened.
