Faulty ambient air temperature sensor (internal open circuit); Damaged, corroded or loose sensor connector or terminals; Open circuit or high resistance in the signal or ground wiring; Signal wire shorted to a voltage supply; Water ingress or corrosion in the connector or wiring behind the front bumper; Fault in the control unit input circuit or shared sensor reference supply.

P0073

Ambient Air Temperature Sensor Circuit A High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
73: FaultThe specific fault in that area

What it means

P0073 means the engine control unit has detected a voltage from the ambient air temperature sensor circuit that is higher than expected, which points to an open circuit, a high resistance or a short to voltage. The control unit sees a signal that suggests an implausibly low temperature, or no valid reading at all. The exact sensor location and how the reading is used differ between models.

Symptoms

Warning light (MIL) on
Incorrect or missing outside temperature reading on the dashboard
Climate control or automatic air conditioning behaving oddly
Slightly rougher cold starts or marginally poorer economy on some models
Intake air or charge calculations affected on models that use the ambient reading

Possible causes

Faulty ambient air temperature sensor (internal open circuit)likely
Damaged, corroded or loose sensor connector or terminalslikely
Open circuit or high resistance in the signal or ground wiringlikely
Signal wire shorted to a voltage supplypossible
Water ingress or corrosion in the connector or wiring behind the front bumperpossible
Fault in the control unit input circuit or shared sensor reference supplyrare

How to diagnose

Read all stored codes and freeze frame data, and note whether the fault is current or intermittent
Check the live ambient temperature reading against the actual outside temperature; a reading stuck at the lowest value suggests an open circuit
Locate the sensor using the model-specific wiring diagram and inspect the connector and wiring for damage, corrosion, water or chafing
Disconnect the sensor and measure its resistance, comparing it with the manufacturer's temperature-resistance specification
Check for the reference voltage at the connector with the ignition on, and confirm the ground circuit is sound
Carry out a wiggle test on the harness while watching the live reading for dropouts
Test the signal wire for continuity back to the control unit and for a short to voltage
Check whether the sensor reading is shared by another module over the network, as procedures vary by model

How to fix

Replace the ambient air temperature sensor if its resistance is out of specification
Clean, repair or replace a corroded or damaged connector and terminals
Repair open circuit, high resistance or chafed wiring in the signal or ground lead
Repair any short to voltage in the signal wire
Seal and protect the connector against water ingress once repaired
Diagnose and repair the control unit or its supply only after the wiring and sensor have been proven good

Can I keep driving?

Low severity

The car can normally be driven as usual, as this fault rarely affects safety or reliability. Book it in for diagnosis soon, as the warning light will stay on and may mask other faults.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.