What is the P0073 Code?
The P0073 error code is a generic powertrain-related code that indicates a problem in the Ambient Air Temperature (AAT) sensor circuit. This sensor, found on most OBD2-equipped vehicles, functions to convert the outside air temperature into an electrical signal. This signal is primarily used by the Powertrain Control Module (PCM) to regulate the air conditioning system and display the outside temperature on the dashboard.
Operation and Causes of the Fault
At startup, after a period of inactivity, the PCM compares the AAT sensor reading with those of the Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensors. The P0073 code is triggered when these values show an abnormal discrepancy. It can also activate if the electrical signal is incorrect once the engine is warm.
This fault is generally caused by an electrical issue, such as an open circuit, a short circuit, or a faulty AAT sensor. A PCM failure is rare but possible.
Symptoms of the P0073 Code
- ⚠️ Malfunction Indicator Lamp (MIL) illuminated on the dashboard.
- ❌ Poor operation or deactivation of the automatic climate control system.
- 🌡️ Incorrect display of the outside temperature on the instrument cluster or center console.
Potential Causes
- Cut wires or an open circuit in the AAT sensor wiring.
- Short circuit to ground or voltage in the circuit.
- Faulty Ambient Air Temperature (AAT) sensor.
- PCM failure (rare).
Diagnosis and Solutions
Start by consulting your manufacturer’s Technical Service Bulletins (TSBs) (Audi, BMW, Ford, VW, etc.) to check for any known issues.
Step 1: Visual Inspection
Locate the AAT sensor, typically situated behind the front grille. Inspect the connector and wiring for any signs of wear, corrosion (greenish tint), or burning. Clean the terminals with an appropriate product and apply dielectric grease.
Step 2: Sensor Testing
Using a multimeter (DVOM), measure the sensor’s resistance (ohms) and compare it to the ambient temperature using a reference chart. A reading of 0 Ω or OL (open circuit) indicates a faulty sensor.
Step 3: Circuit Testing
With a diagnostic tool, read the AAT sensor’s voltage or temperature. It should be around 5 V (ignition on) or display a very low temperature. By shorting the two terminals of the connector with a jumper wire, the reading should drop to near 0 V or show a very high temperature. If not, the circuit or the PCM is at fault.
Step 4: Replacement
If all tests point to the sensor, replace it. Clear the codes and perform a road test to confirm the repair. If the code reappears, a PCM failure is possible, requiring reprogramming or replacement by a professional.
Need help? Electrical diagnosis can be complex. If you are unsure, consult a qualified mechanic to avoid damaging other electronic components in your vehicle.