DTC P0072 — Ambient Air Temperature (AAT) Sensor Circuit Low.

📘 DTC P0072 – Ambient Air Temperature Sensor Circuit Low

Meaning

The ECU sees the AAT sensor signal voltage lower than expected.
This usually indicates short-to-ground, sensor failure, or wiring issues.

📌 Symptoms

Wrong outside temperature reading on cluster (very low or “– – °C”)

Poor AC cooling performance

AC compressor cycle irregular

Possible effect on engine warm-up strategy in some cars

MIL may or may not illuminate

📌 Common Causes

1. Faulty AAT sensor (thermistor shorted)

2. Wiring short to ground

3. Damaged connector / corrosion

4. Open 5V reference (in some vehicles uses 5V)

5. Rodent damage to front bumper wiring

6. Sensor installed incorrectly after bumper repair

📐 Wiring Basics

Ambient Air Temp Sensor = NTC thermistor

Low temp → high resistance → high voltage

High temp → low resistance → low voltage

P0072 = Voltage too low = Sensor sees very high temperature (wrong), usually wiring ground short.

🔧 Diagnostic Procedure (Step-by-Step)

1. Visual Inspection

Locate sensor (usually front bumper / grille area)

Check:

Broken sensor

Corroded connector pins (very common)

Exposed wiring

Damage from road debris

2. Scan Tool Check

Check live data:

Ambient temperature reading (°C)

If reading is extremely high (e.g., +80°C to +140°C), the circuit is shorted.

3. Sensor Testing (Multimeter)

A. Resistance Test

Disconnect sensor → measure Ω.

Typical values:

Temperature Expected Resistance

0°C 9–10 kΩ
20°C 2–3 kΩ
40°C 1 kΩ

If resistance = very low (< 200Ω) → Sensor shorted → Replace.

B. Voltage Test (Key ON)

Back-probe harness:

Signal wire: usually 2.5–5V

Ground wire: 0V

If signal wire = 0–0.5V → short to ground

4. Harness Testing

If sensor is OK:

Check continuity of both wires to ECU

Look for short to ground

Look for short to another circuit

Flex the wiring around bumper; intermittent shorts are common.

5. Replace Sensor if Faulty

AAT sensors are cheap and easy:

1-pin clip removal

Push-fit replacement

After replacement:

Clear code

Check live data again

AC performance should normalize

Welcome to madurai car service 💐🙏🏻.