P2ACA: Charge Air Cooler Coolant Temperature Sensor B Circuit High
What to do
Expect reduced power when the engine is worked hard or in hot weather, and normal power otherwise. The charge air cooler has its own separate coolant circuit — check that its level is correct and that it has been bled, because that is a commoner cause than the sensor.
What this code means
The circuit for the second charge air cooler coolant temperature sensor is faulty.
A water-cooled charge air cooler is what lets a small turbocharged engine behave like a larger one, and this sensor is how the car knows it is working.
Compressing air heats it, and hot air is thin. A turbocharger that raises pressure also raises temperature, which undoes part of what it achieved — and hot intake air brings detonation with it, so the engine must retard timing to stay safe. Cooling the charge recovers both the density and the timing.
An air-to-water cooler does that in a fraction of the space an air-to-air intercooler needs, which is why it appears on compact and heavily boosted engines. The price is a second low-temperature coolant circuit with its own pump and radiator — a system quite separate from the engine's own cooling, and frequently forgotten at service time.
Which is why the failure most often found here is not the sensor. It is that circuit having lost coolant or gained air, so a second sensor reading oddly is worth treating as a question about the circuit rather than about the part.
The symptom is heat-dependent and easy to miss: full power when cool, noticeably less on a long climb or a hot day, because the engine is retarding timing to protect itself.
At or above the upper limit, usually an open circuit floating the input high.
Likely causes
Start here
- Faulty charge air cooler coolant temperature sensor · specialist
- Corroded or loose connector · specialist
- Open circuit in sensor wiring · specialist
Less common
- Low coolant level · moderate
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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