P0073 - Ambient Air Temperature Sensor Circuit High Input
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0073 is a diagnostic trouble code (DTC) for Ambient Air Temperature (AAT) Sensor Circuit High Input. This occurs when the Engine Control Module (ECM) detects a voltage return from the AAT sensor that is higher than the calibrated limit (typically above 4.8V). This logic usually indicates an open circuit. The AAT sensor is an NTC thermistor; a break in the wiring or a failed sensor element results in maximum reference voltage being seen by the ECM. This data is shared across the CAN-bus and is vital for HVAC operation, fuel trim adjustments, and diesel particulate filter (DPF) regeneration logic.
Possible Causes
Defective Ambient Air Temperature (AAT) sensor (internal open)
Wiring harness break in signal or ground circuit
Corroded or loose connector pins causing an open circuit
Faulty Engine Control Module (ECM) or Instrument Cluster
Symptoms
Recommended Solution
- Visual Inspection: Locate the sensor (typically behind the front grille or in the side mirror). Check for harness damage or rodent bites.
- Connector Inspection: Unplug the sensor and check for corrosion/green crust on pins. Use contact cleaner if necessary.
- Resistance Test (Sensor): Use a multimeter to measure Ohms across the sensor pins. An infinite reading (O.L) confirms an internal open circuit. Normal range is typically 2k-5k Ohms at 20°C.
- Voltage Test (Harness): With ignition ON, check for 5V reference and a clean ground at the connector. If 5V is missing, trace wiring back to the ECM.
- Component Replacement: Replace the AAT sensor if it fails the resistance test.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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