P0539
A/C Evaporator Temperature Sensor Circuit Intermittent
- Severity
- Low
- Driving
- No driving restriction
The evaporator temperature signal is dropping out intermittently. Cooling may work perfectly and then stop, often after the system has been running for a while - which is also what genuine icing looks like.
Possible causes
- CommonFailed evaporator temperature sensor
- CommonCorroded connector or damaged wiring
- CommonSensor dislodged from its position in the evaporator
- PossibleWater ingress from a blocked evaporator drain
- PossibleLoss of reference voltage or earth
What you might notice
- Air conditioning not cooling, or cooling intermittently
- Evaporator freezing and airflow dropping away
- Compressor cycling rapidly
- Musty smell from the vents
- Check engine light on
What to check, in order
- Compare the reported evaporator temperature with ambient on a system that has been off overnight - they should be close.
- Check the evaporator drain is clear. A blocked drain fills the housing with water, which reaches the sensor and its connector.
- Inspect the connector for corrosion and water.
- Check the reference voltage and earth at the sensor.
- Note that this sensor exists to stop the evaporator freezing solid. If airflow drops away after ten minutes of use, the evaporator is icing and the sensor is not doing its job.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Vehicle speed control, idle control and auxiliary inputs
P0500P0501P0502P0503P0504P0505P0506P0507P0508P0509P0510P0511P0512P0513P0514P0515P0516P0517P0518P0519P0520P0521P0522P0523P0524P0525P0526P0527P0528P0529P0530P0531P0532P0533P0534P0535P0536P0537P0538P0539P0540P0541P0542P0543P0544P0545P0546P0547P0548P0549P0550P0551P0552P0553P0554P0555P0556P0557P0558P0559P0560P0561P0562P0563P0564P0565P0566P0567P0568P0569P0570P0571P0572P0573P0574P0575P0576P0577P0578P0579P0580P0581P0582P0583P0584P0585P0586P0587P0588P0589P0590P0591P0592P0593P0594P0595P0596P0597P0598P0599