P0073 indicates the Powertrain Control Module (PCM) has detected a high voltage signal from the Ambient Air Temperature (AAT) sensor circuit. The AAT sensor is a temperature-dependent resistor (thermistor); when the circuit reads abnormally high, it typically means the sensor has gone open, the wiring has high resistance, or a connector fault is interrupting the voltage divider the PCM relies on.
The thermistor inside the sensor most commonly fails open, which causes the PCM to read the full reference voltage as a 'high' signal. This is the single most frequent cause of P0073.
A break, chafe, or stretched conductor in the signal or ground wire to the AAT sensor produces the same high-voltage reading. Wires near the front grille are exposed to road debris, heat, and vibration.
The AAT sensor connector is typically exposed to the elements behind the grille or in a mirror housing. Moisture intrusion and pin corrosion create high resistance that the PCM sees as a high circuit value.
If the sensor has been knocked out of position or is touching an engine-bay heat source, it can report implausibly high temperatures that the PCM flags as a circuit fault. This is less common than an electrical failure but worth checking.
Because the AAT sensor shares a reference voltage and sometimes a ground with other sensors, a fault elsewhere on that circuit can elevate the AAT reading. Less common, but possible.
A failure inside the PCM that pulls or misreads the AAT signal is occasionally reported but is uncommon. PCM replacement should only be considered after the sensor, wiring, and connectors have all been thoroughly ruled out.
Generally yes. P0073 does not typically affect drivability, emissions readiness, or safety. You may notice an incorrect outside temperature reading and slight A/C behavior changes, but the vehicle should run normally.
It is usually mounted in the lower front grille area, behind the front bumper, or in an outside side mirror, where it is exposed to true outside air but shielded from direct engine heat.
Clearing the code will turn the light off temporarily, but if the underlying fault is still present the code will return. The real problem (sensor or wiring) should still be addressed because it can affect climate control behavior and may set additional codes over time.
Almost never. Despite what you may see suggested online, P0073 is virtually always caused by the sensor itself, a wiring issue, or a connector problem. Replacing or reprogramming the PCM is an expensive step that should only be considered after the sensor, harness, and connectors have all been verified good, which is rarely the case.