P0070 — Ambient Air Temperature Sensor Circuit A

Causes

• Open or short in the AAT sensor wiring
• Corroded, damaged, or loose AAT sensor connector
• Failed ambient air temperature (NTC) sensor
• Short to battery voltage or short to ground
• Poor ground or reference voltage to sensor
• PCM input circuit fault or intermittent PCM connection

Symptoms

• Diagnostic trouble code stored and MIL illumination (may vary by vehicle)
• Incorrect ambient temperature reading on climate or instrument display
• HVAC automatic temperature control may behave incorrectly
• Cold-start enrichments or emissions-related strategies may be affected
• Possible intermittent or constant fault depending on wiring condition

What to check

• Read freeze-frame and live AAT sensor data with a scan tool; note displayed temperature and any obvious fixed values (e.g., -40°C or a max value).
• Compare AAT reading to actual ambient temperature (digital thermometer).
• Visually inspect sensor location, connector, and wiring for damage, corrosion, or water intrusion.
• Back-probe connector and measure sensor voltage with key ON, engine OFF (verify reference and signal).
• Measure sensor resistance at ambient and when warmed/cooled to confirm thermistor behavior (resistance should change with temperature).
• Check for continuity between sensor signal and PCM; check for shorts to battery and ground.

Signal parameters

• Typical AAT sensor type: NTC thermistor — resistance decreases as temperature increases.
• Typical expected output: roughly 0.1–4.9 V signal range depending on circuit design (varies by manufacturer).
• Common ambient operating range: approximately -40°C to +85°C (sensor and PCM limits vary).
• A reading of exactly -40°C or a fixed/max value often indicates open circuit or short condition.
• Resistance will change noticeably when sensor is warmed/cooled (use a thermometer to correlate).

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