DTC P0073 – Ambient Air Temperature (AAT) Sensor Circuit High.

✅ P0073 — Ambient Air Temperature Sensor Circuit High

Meaning:
The PCM/ECM is detecting an unusually high voltage from the Ambient Air Temperature sensor circuit.
This usually indicates an open circuit, broken wire, or sensor unplugged.

The AAT sensor is usually located in the front bumper, grille, or near the radiator support.

✅ Common Symptoms

Incorrect outside temperature reading on cluster

AC not cooling properly / delayed AC operation

Poor automatic climate control behaviour

Possible AC compressor not engaging in some cars

✅ Most Common Causes

1. Sensor unplugged or loose connector

2. Broken wire / open in harness near front bumper

3. Corroded connector pins

4. Faulty Ambient Air Temperature sensor

5. High resistance in circuit

6. Rodent damage (very common near bumper wiring)

🔧 Step-By-Step Diagnosis for P0073

1. Visual Inspection

Check AAT sensor near bumper/grille

Inspect connector for:

Loose fit

Damaged pins

Corrosion or moisture

Check wiring for:

Cuts

Rodent bites

Broken insulation

Wiring tension after bumper repair

👉 If sensor unplugged → plug in → clear code → recheck.

2. Check Sensor Resistance (With Multimeter)

A typical AAT sensor is a NTC thermistor.

Approx. values:

Cold temp → high resistance (20k–30k ohm at 0°C)
Warm temp → low resistance (1k–3k ohm at 30°C)

If infinite resistance → sensor open → replace.

3. Check Power & Ground at Connector

You should see:

5V reference from PCM

Ground return

If 5V is present but sensor side open:

→ Sensor faulty

If 5V missing:

→ Open in wiring harness

4. Wiggle Test

Move the harness while watching the scan tool:

If temperature reading jumps or becomes –40°C (common default value) → wiring open.

5. Replace Sensor (If Needed)

• Sensor is usually inexpensive (₹300–₹1200 depending on brand).
  After replacement:

Clear codes

Confirm temperature reading is accurate

✅ Quick Fix Direction

⭐ 80% of P0073 cases = open circuit / broken wire
⭐ 15% of cases = faulty sensor
⭐ 5% = corrosion in connector

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