✅ DTC P0099 – Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

Meaning:
The ECU detects an unstable or intermittent signal from the Intake Air Temperature Sensor 2 (IAT2).
IAT2 is usually located after the turbo/intercooler, depending on the vehicle.

🔧 Common Symptoms

Intermittent check engine light

Rough acceleration

Poor fuel economy

Turbo boost fluctuation

Hard starting (rare)

🔍 Common Causes

1. Loose or corroded IAT2 connector

2. Damaged wiring harness (rubbed, melted, cracked)

3. Faulty IAT2 sensor

4. Intercooler leak causing unstable temp readings

5. Moisture inside connector

6. ECU internal fault (rare)

🛠️ Step-By-Step Diagnostic Procedure

1. Visual Inspection (first step)

Locate IAT Sensor 2 (usually on charge air pipe or intercooler outlet).

Check:

Connector fitment

Bent or pushed-back pins

Corrosion or oil contamination

Wiring damage

👉 If anything is suspicious, fix and clear codes.

2. Wiggle Test (very important for intermittent codes)

With engine idling, wiggle the wiring harness near the sensor.

If RPM fluctuates or code resets → wiring/connector fault confirmed.

3. Check Sensor Voltage

Using a multimeter:

With ignition ON:

5V reference should be present on one pin.

Ground continuity on another pin.

Signal wire should show 1–4 V, depending on temperature.

abnormal readings → sensor or wiring fault

4. Check Sensor Resistance (IAT2 element test)

Remove the sensor and measure:

Typical NTC sensor reading:

At 20°C: 2–3 kΩ

At 40°C: 1.0–1.5 kΩ

At 80°C: 0.2–0.3 kΩ

If resistance jumps or is open → replace sensor

5. Check for Boost Leak / Intercooler Leak

Because IAT2 is after turbo, leaks cause unstable temperature:

Broken clamps

Cracked intercooler pipe

Leaking intercooler

Fix leak → clear code.

6. Check ECU (last step)

If all wiring and sensor check out:

Back-probe at ECU connector to confirm signal stability.

If sensor signal is stable at sensor but unstable at ECU → wiring/ECU fault.

🔧 Most Common Fixes

💫 Tightening or cleaning IAT2 connector
💫 Replacing IAT2 sensor
💫 Repairing wiring harness
💫 Fixing intercooler/boost pipe leak
💫 Cleaning oil contamination from connector

Welcome To Madurai Car Service 💐🙏.