DTC P0112 – Intake Air Temperature (IAT) Sensor Circuit Low Input.

✅ DTC P0112 — IAT Sensor Circuit Low Input

📌 Meaning

The ECM detects that the Intake Air Temperature sensor (IAT) is sending a voltage lower than normal.
This corresponds to very high temperature reading (ECM thinks air is extremely hot).

🔧 Common Causes

Most common (check first):

1. IAT sensor shorted to ground

2. Damaged wiring harness (rubbed, melted, rodent bite)

3. Connector corrosion or loose terminals

4. IAT sensor internal failure

Less common:

5. MAF sensor IAT portion failed (many cars have combined MAF+IAT)

6. ECM 5V reference issue

7. Aftermarket air filters / oiled filters contaminating the sensor

🔍 Symptoms

Hard starting

Poor acceleration

Black smoke (diesel)

Hesitation

Low fuel efficiency

Radiator fan running continuously

Check Engine Light ON

🧰 Step-by-Step Diagnosis (Mechanic Level)

1. Visual Inspection

Check IAT sensor and wiring near air intake hose.

Look for:

Broken wires

Exposed wires touching ground

Loose connector

Corrosion pins (green/white deposits)

Fix any wiring issues → Clear code → Test.

2. Scan Tool Live Data

Check IAT temperature reading with key ON, engine cold.

Expected:

Ambient temperature ±5°C.

If IAT shows:

–40°C → open circuit

+120°C or higher → short to ground (likely cause for P0112)

If temperature is +120°C → proceed to wiring check.

3. Measure IAT Sensor Voltage (Multimeter)

At connector (sensor unplugged):

One pin = 5V reference

Other pin = signal return (should show 5V without sensor)

If signal pin is 0V, the wire is shorted to ground.

4. Check Sensor Resistance

IAT is a thermistor.

Approx resistance values:

Temperature Resistance (approx)

0°C 10k – 12k Ω
20°C 2k – 3k Ω
40°C 1k Ω

If it shows very low resistance (0–100Ω) → sensor shorted → Replace sensor.

5. Wiggle Test

Keep engine running + monitor IAT live data.

Wiggle wiring from air filter box to harness.

If value jumps → wiring fault.

6. Check Combined MAF+IAT Sensor (if applicable)

Many modern cars have IAT built into the MAF.

If the IAT is reading wrong but wiring is OK → Replace MAF assembly.

7. ECM Issue (rare)

Only consider if:

Wiring is good

Sensor is new

Still no 5V or false readings

Check continuity from sensor to ECM pins.

🔧 Most Common Repairs

🌟 Replace IAT sensor
🌟 Repair short to ground in wiring
🌟 Clean or repair connector
🌟 Replace MAF sensor (if IAT integrated)
🌟 Repair 5V reference circuit

🕒 Labour Time Estimate

Diagnosis: 15–25 minutes

Sensor replacement: 5–10 minutes

Wiring repair: 15–30 minutes

Welcome To Madurai Car Service 💐🙏.