Code
P0072
Generic
P — Powertrain
Ambient Air Temperature Sensor Circuit A Low
Views:
UK: 28
EN: 33
RU: 41
AI status
Completed
Completed
100%
Causes
- Short to ground in AAT sensor signal circuit
- Faulty ambient air temperature sensor (thermistor)
- Damaged, corroded, or disconnected connector
- Open or shorted wiring between sensor and control module
- Poor ground or reference voltage at the sensor circuit
- Faulty engine/BCM/ECM input (rare)
Symptoms
- Incorrect or very low ambient air temperature reading on dash or HVAC display
- Automatic HVAC climate functions may operate incorrectly
- Check Engine Light or MIL illuminated (depending on vehicle)
- Climate control auto modes, A/C or fan behavior may be erratic
- Some vehicles may show reduced range/efficiency estimates (EV/hybrid)
What to check
- Scan tool: read P0072, freeze frame and freeze data, and view live ambient air temp PID
- Visually inspect sensor location, connector, and wiring for corrosion, damage, or water intrusion
- Wiggle test wiring harness while watching live ambient temp PID to look for intermittent changes
- Measure sensor harness voltage with key ON (reference voltage usually ~5 V) and measure signal voltage at harness
- Measure sensor resistance at ambient temperature after unplugging sensor and compare to manufacturer spec (many are NTC style; common example: ~10 kΩ @ 25°C — verify SVM for vehicle)
- Check for short to ground on the signal wire using a multimeter
Signal parameters
- Typical reference supply: ~5 V (vehicle-specific; some use 12 V or other references — check service manual)
- Expected signal voltage range during normal operation: roughly 0.2–4.8 V depending on temperature and sensor design
- Circuit A Low condition generally means signal voltage below the lower threshold (e.g., < ~0.2 V) — exact thresholds are vehicle-specific
- Common sensor type: NTC thermistor (resistance decreases as temperature increases); many are ~10 kΩ at 25 °C (confirm spec)
- Resistance vs. temperature is sensor-specific; always compare measured resistance to OEM chart
Diagnostic algorithm
- Retrieve codes and live data. Note freeze frame and ambient air temp PID value.
- Visually inspect sensor, mounting, and harness for damage, corrosion, or water entry. Repair obvious issues.
- With key ON (engine OFF), backprobe the sensor connector: verify reference voltage and ground are present at the harness. If reference is missing, trace to control module/fuse.
- Measure signal voltage at the harness. If signal is very low (< manufacturer low threshold), suspect short to ground between sensor and module.
- Unplug sensor and measure resistance across sensor terminals at ambient temperature. Compare to spec. If resistance is out of range, replace sensor.
- If sensor resistance is within spec, check continuity and insulation of signal wire to the control module; repair any short to ground or open circuit.
- After repairs, clear codes and perform test drive or monitor live data to confirm proper ambient temperature readings and that code does not return.
- If wiring and sensor are good and fault persists, consider control module input fault and perform module-level diagnostics per manufacturer procedures.
Likely causes
- Corroded or pushed-out connector at the sensor
- Pinched or chafed harness causing a short to chassis ground
- Failed thermistor element inside sensor
- Missing or damaged sensor sealing allowing water intrusion
- Loose or faulty ground or reference supply from module
Fault status
Status
P0072 — Ambient Air Temperature Sensor Circuit A Low: low voltage/signal detected on ambient air temperature sensor circuit.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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