P0D79
A/C Compressor Control Module Output Driver Temperature Sensor Circuit Intermittent/Erratic.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- D
- AreaReserved
- 79
- FaultThe specific fault in that area
What it means
P0D79 means the A/C compressor control module has seen an intermittent or erratic signal from the temperature sensor that monitors its output driver (the power stage that runs the compressor motor). The module expects a smooth, plausible temperature reading. It set the code because the signal jumped, dropped out or disagreed with expected values. This is mainly found on vehicles with an electrically driven A/C compressor, and the exact layout depends on the model.
Symptoms
- A/C blowing warm or cooling only intermittently
- A/C compressor cutting out or not starting at times
- Air conditioning warning light or general fault message on the dash
- Reduced cooling performance in hot weather or at idle
- Fault code that comes and goes, often with vibration or temperature changes
Possible causes
- Loose, corroded or damaged connector or terminals at the compressor control module or its wiringlikely
- Chafed, broken or high-resistance wiring in the sensor circuit or its reference and groundlikely
- Fault in the output driver temperature sensor inside the compressor control modulepossible
- Low or unstable supply voltage or a poor earth to the compressor modulepossible
- Moisture or coolant or refrigerant oil contamination in the connector or modulepossible
- Internal fault of the compressor control module or outdated software, if the manufacturer lists it as a known issuerare
How to diagnose
- Read all stored and pending codes and note freeze frame data, including ambient and system conditions when the fault set.
- Check for related codes such as supply voltage, communication or compressor faults, and deal with those first.
- Inspect the compressor module connector and wiring for damage, corrosion, moisture, pushed-back pins and rubbing points.
- With the system running, gently wiggle the harness and connector while watching live data for the driver temperature reading to jump or drop out.
- Check battery condition, charging voltage and the module's supply and earth connections for voltage drop under load.
- Check the live temperature reading against the expected value when the system is cold, then after running, looking for implausible steps.
- Test the sensor circuit wiring for continuity, short circuits and resistance using the manufacturer's wiring diagram for that model.
- Check for manufacturer service information or software updates for the compressor module, and only then consider module replacement.
How to fix
- Clean, repair or replace faulty connectors and terminals, and secure the harness away from rubbing points.
- Repair or replace damaged wiring in the sensor circuit, including reference and earth.
- Correct low voltage or poor earth faults in the supply to the compressor module.
- Replace the compressor or control module if the internal sensor or driver is faulty, following the manufacturer's procedure.
- Apply a manufacturer software update to the module where an outdated calibration is a known cause.
- Clear the code after repair and road test to confirm it does not return.
Can I keep driving?
The car is usually safe to drive, but the A/C may be reduced or disabled while the fault is present. On some hybrid and electric models the same system helps cool the battery, so check the manufacturer's guidance and have it checked soon, particularly in hot weather.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.