P0073
Ambient Air Temperature Sensor Circuit High Input
If your code reader dashboard displays the generic DTC error code P0073, your vehicle is currently experiencing an active failure related to "Ambient Air Temperature Sensor Circuit High Input". Proper system troubleshooting is required to safely clear this warning.
Driver's Summary
A P0073 fault code points directly to a problem with ambient air temperature sensor circuit high input that the ECM has confirmed over multiple drive cycles. The most common signs are a/c system malfunction, incorrect outside temp display, check engine light. You can continue normal driving, but schedule an inspection at your next service appointment to clear this code properly.
Symptoms
A/C system malfunction, incorrect outside temp display, check engine light
Common Causes
- Unplugged ambient temperature sensor
- Faulty ambient air temperature sensor
- Broken wire in sensor harness
- Corrosion in sensor plug
How to Fix
- 1 Reconnect sensor plug
- 2 Replace ambient air temperature sensor
- 3 Repair broken wires behind grille
- 4 Clean connector contacts
Technical Explanation
P0073 is stored after the control module confirms the fault over multiple ignition cycles, ruling out transient electrical noise as the cause. The diagnostic runs during closed-loop operation only, ensuring the engine is at full operating temperature and the PCM's fuel trim feedback loop is active before confirming any out-of-range condition. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
This code won't strand you, but it shouldn't be ignored indefinitely. The unplugged ambient temperature sensor issue identified by P0073 can mask other developing problems and will cause an automatic emissions test failure in most states.
Mechanic's Pro Tip
The most common mistake with P0073 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Ambient temp sensor: $20 - $80; Labor: $50