Code
P0073
Generic
P — Powertrain
Ambient Air Temperature Sensor Circuit A High
Views:
UK: 20
EN: 38
RU: 69
AI status
Completed
Completed
100%
Causes
- Open circuit in ambient air temperature sensor wiring
- Short to battery voltage (12V) in sensor harness
- Corroded, loose, or water-damaged sensor connector
- Failed ambient air temperature sensor (thermistor open or out of range)
- Poor ground at sensor or ECM connector
- Faulty ECM (rare)
Symptoms
- Incorrect outside/ambient temperature display on dash or HVAC screen
- Climate control may behave improperly (incorrect automatic mode or fan operation)
- Possible inability for HVAC to enter some automatic functions
- No effect on engine drivability in most cases
- Malfunction indicator lamp (MIL) or service message may be illuminated
What to check
- Retrieve freeze frame and live data with a scan tool; note AAT voltage and temperature readout
- Visually inspect sensor location, wiring harness, and connector for damage or corrosion
- Backprobe the sensor connector and measure signal voltage with key ON, engine OFF
- Measure sensor resistance at ambient temperature and compare to expected NTC behavior
- Unplug sensor and observe scan tool reading (open should usually return a specified high value or fault)
- Check continuity between sensor connector and ECM pin and check for short to 12V or battery
Signal parameters
- Sensor type: NTC thermistor (resistance decreases as temperature rises) in most vehicles
- Typical signal: 0.0–5.0 V; open/high condition often reports near battery voltage or above normal expected range
- High circuit fault threshold: voltage significantly above normal operating range (commonly >4.5 V) or open circuit
- Resistance behavior: high resistance at cold, lower resistance at warm (specific ohms vary by manufacturer)
Diagnostic algorithm
- Clear codes and attempt to re-create: confirm P0073 returns and note freeze-frame/live data.
- With key ON (engine OFF), observe AAT sensor voltage and displayed ambient temperature on scan tool.
- Visually inspect sensor and connector for water, corrosion, broken pins, or mechanical damage.
- Backprobe sensor signal and ground terminals: measure voltage. If signal is near battery voltage or absent, suspect open or short to 12V.
- Unplug sensor: many systems will show a defined fail-safe value or open-circuit voltage; compare behavior to factory data.
- Measure sensor resistance at ambient temperature and while changing temperature (ice water and warm water) to confirm thermistor response.
- Check continuity between sensor signal and ECM pin and verify there is no short to battery (+12V) and the ground return is good.
- Repair any damaged wiring or connector corrosion. If wiring and connector are good and sensor does not change resistance with temperature, replace the sensor.
- After repair or replacement, clear codes and confirm proper ambient temperature reading and that P0073 does not return on road/test cycle.
- If fault persists and wiring/drain checks good, consider ECM input fault and consult manufacturer diagnostics before replacing ECM.
Likely causes
- Broken or disconnected sensor wire (pinched, chafed, or disconnected)
- Connector contamination or corrosion causing intermittent/open signal
- Sensor removed or damaged by road debris or exposure
- Aftermarket component incorrectly wired
- Short to 12V caused by previous repairs or rodent damage
Fault status
Status
Ambient Air Temperature Sensor Circuit A High — sensor circuit voltage/resistance is higher than expected (open circuit or short to battery voltage).
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email