P2518: Air Conditioning Refrigerant Pressure Sensor B Circuit High
What to do
Expect the air conditioning to stop working — the module is disengaging the compressor to protect it. Look at the front of the condenser for leaves, insect debris or road dirt, and check the cooling fans run when the air conditioning is switched on; both are free and both cause genuinely high pressure. If the system has been topped up from a canister, say so. Refrigerant is specified by weight and an overfilled system cools worse, not better, while running at pressures the parts were not designed for.
What this code means
The second refrigerant pressure sensor circuit reads above its valid range — an open circuit, a disconnected sensor, or a genuinely over-pressured system.
That last case is worth separating from the wiring ones, because it is a real condition with a real cause and the module's response to it is protective. High refrigerant pressure means the system cannot reject its heat, and the compressor is disengaged to stop it damaging itself or bursting a hose. The reasons are mostly physical and mostly visible: a condenser blocked with leaves, insects or road debris, cooling fans that are not running, or a system that has simply been overfilled.
Overfilling deserves naming because it is self-inflicted and increasingly common. The refrigerant charge is specified by weight to within a few tens of grams, and topping up from a canister without weighing what goes in is guesswork. An overcharged system cools worse than a correctly charged one, not better, and it runs at pressures the components were not designed for.
So the checks before the sensor: look at the condenser, confirm the fans run with the air conditioning on, and ask whether the system has been topped up rather than properly evacuated and recharged.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Blocked or restricted condenser · moderate
- Overcharged refrigerant system · moderate
- Cooling fans not operating · moderate
Less common
Symptoms
Components involved
Information, not instruction
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