DTC P007400 – Ambient Air Temperature (AAT) Sensor Circuit Intermittent.

✅ What P0074 Means

P0074 indicates that the Ambient Air Temperature sensor signal is cutting in and out—sometimes reading correctly and sometimes dropping out due to wiring, connector, or sensor issues.

This fault is common in vehicles where the AAT sensor is mounted in the front bumper, grille, or mirror, where it is exposed to weather and road debris.

🔧 Common Symptoms

Outside temperature display jumps or is inaccurate

A/C system performance issues (delayed cooling)

Intermittent A/C compressor engagement

Intermittent MIL (Check Engine)

🔍 Most Common Causes

1. Loose / corroded AAT sensor connector (MOST common)

2. Damaged wiring near the bumper / grille

3. Sensor internal failure (open → closed intermittently)

4. Water intrusion inside connector

5. Poor ground or reference signal intermittently breaking

6. Front-end impact damage / harness pulled

🧰 Step-by-Step Diagnosis Guide

1. Visual Inspection

🌟 Locate the Ambient Air Temp Sensor (usually front bumper/grille).
Check for:

Broken sensor housing

Loose connector

Corroded terminals (green/white powder)

Rubbed or cut wiring

Moisture inside connector

👉 If corrosion found → clean and apply dielectric grease.

2. Check Connector Fitment

Gently wiggle the connector while engine is ON.

If temperature reading fluctuates → connector/wiring issue (intermittent).

3. Check AAT Sensor Resistance

AAT is an NTC thermistor (resistance decreases as temperature increases).

Typical values:

0°C → 32 kΩ

20°C → 2.5–3.0 kΩ

40°C → 1 kΩ

Use a multimeter across the 2 sensor pins.

If resistance jumps when you tap or move the sensor, → sensor is faulty.

4. Check the 5V Reference & Ground (if applicable)

Some vehicles use a voltage divider:

Reference: 5V

Ground: 0V

At the sensor connector:

One wire should have ~5V

Other should be ground

Voltage should not drop while wiggling the harness

If voltage cuts out intermittently → harness or ECM pin issue.

5. Check Live Data on Scanner

Monitor Ambient Air Temp.

Do this:

Wiggle the harness

Move the bumper gently

Spray cold/hot air on the sensor

If reading jumps:

→ Intermittent circuit / sensor internal failure.

🛠 Common Fixes

⭐ Clean or tighten AAT sensor connector
⭐ Repair broken or corroded wiring
⭐ Replace Ambient Air Temperature Sensor
⭐ Secure the harness using clips
⭐ Clean ground points if related

🚗 When to Replace the Sensor

Replace when:

Resistance is unstable

Sensor responds slowly

Sensor reading drops out on live data

Any physical damage seen

AAT sensors are inexpensive, so replacement is common.

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