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P0099 – Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic (OBD2)

P0099 means "Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic". The intake air temperature (IAT) sensor signal briefly drops out or jumps. The fault comes and goes – often with vibration, heat or moisture – so the part may test fine in the workshop.

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P0099 quick summary

Fault codeP0099
MeaningIntake Air Temperature Sensor 2 Circuit Intermittent/Erratic
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. The engine uses a substitute temperature, so you may notice slightly harder starting or higher fuel consumption. Have it fixed at the next opportunity.
Repair cost€15 – €200

How the intake air temperature sensor works

The intake air temperature sensor tells the engine control unit how warm the incoming air is, so it can correct the fuel quantity, ignition timing and boost for the air density.

The IAT sensor is a thermistor (NTC resistor): its resistance falls as the temperature rises. It is often built into the MAF sensor or MAP sensor, or mounted separately in the intake duct or intake manifold. Engines with a turbocharger frequently have a second intake air temperature sensor after the intercooler (IAT 2), which is why codes for sensor 2 exist.

Cold air is denser and contains more oxygen than warm air, so the control unit adds fuel when it is cold and retards ignition when the intake air is very hot to prevent knocking. A wrong IAT signal does not usually cause dramatic symptoms, but it affects starting, fuel consumption and emissions.

Codes like P0127 (intake air temperature too high) are not electrical faults but a warning that the measured temperature is really too high – for example because of a blocked intercooler or hot air being drawn in from the engine bay.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16483 (P0099). Both numbers mean the same fault.

Symptoms of P0099

  • Check Engine light on
  • Slightly harder cold or hot starting
  • Higher fuel consumption
  • Reduced power or knocking in hot weather (P0127)
  • Often no noticeable symptoms at all

Most common causes of P0099 (most likely first)

Mechanic's Pro Tip

Compare the IAT reading with the coolant temperature after the car has stood overnight. If they differ by more than about 5 °C on a cold engine, one of the two sensors is wrong – this simple check avoids replacing the wrong part.

  1. 1.Loose or corroded connector pin

    Most likely

    Pins that have spread lose contact as the engine vibrates.

  2. 2.Chafed wire that shorts only now and then

    Often where the harness moves with the engine.

  3. 3.Internal intermittent fault in the intake air temperature (IAT) sensor

  4. 4.Faulty IAT sensor

    Thermistors age or break internally; on combined sensors the whole MAF or MAP unit may need replacing.

  5. 5.Sensor dirty or coated with oil

    An oily sensor reacts slowly to temperature changes.

  6. 6.Intercooler blocked or hot air intake (P0127)

    A dirty intercooler, a missing intake duct or an air box drawing hot engine-bay air makes the air really too warm.

  7. 7.Fault in the control unit

    Rare, but possible when wiring and sensor test fine.

Step-by-step diagnostic guide

  1. 1

    Read codes and live temperature

    Read all codes and look at the intake air temperature in live data. On a cold engine that has stood overnight, the IAT should match the outside air and coolant temperature within a few degrees.

  2. 2

    Do a wiggle test

    With the engine running and the intake air temperature (IAT) sensor value in live data, gently move the harness and connector. If the value jumps or the code returns, the fault is in that section. Also check pin tension with a matching terminal.

  3. 3

    Check for implausible values

    A reading of around –40 °C usually means an open circuit; a reading of +130 °C or more usually means a short to ground. A reading that is realistic but wrong points to the sensor itself.

  4. 4

    Measure the sensor resistance

    Unplug the sensor and measure its resistance at a known temperature, then warm it gently with a hairdryer – the resistance must drop smoothly.

    Multimeter: Typical NTC values: roughly 2–3 kΩ at 20 °C and a few hundred ohms at 80 °C (check the exact table for your sensor).

  5. 5

    Check wiring and connector

    Check the reference and ground wires for continuity and the connector for corrosion or water.

  6. 6

    Replace the sensor or fix the hot-air cause

    Replace the sensor if its resistance is wrong. For P0127, clean the intercooler, check the intake ducting and make sure the engine is not drawing hot engine-bay air.

Frequently asked questions

Can I keep driving with P0099?

Yes. The engine uses a substitute temperature, so you may notice slightly harder starting or higher fuel consumption. Have it fixed at the next opportunity.

How much does it cost to fix P0099?

Typical repair costs are 15 € – 200 €, depending on the cause and the vehicle. The most common fixes are: loose or corroded connector pin; chafed wire that shorts only now and then; internal intermittent fault in the intake air temperature (IAT) sensor. Always confirm the cause with the tests above before buying parts.

Where is the intake air temperature sensor?

It is usually built into the MAF sensor or the MAP sensor, or screwed into the air duct or intake manifold. Turbo engines often have a second sensor after the intercooler.

Does a bad IAT sensor cause poor fuel economy?

It can. If the sensor reports colder air than reality, the engine injects more fuel than needed. The effect is usually small but noticeable over time.

What is the difference between P0099 and similar codes?

P0099 belongs to a group of codes for the same component that differ in the type or location of the fault: P0096 – Intake Air Temperature Sensor 2 Circuit Range/Performance; P0097 – Intake Air Temperature Sensor 2 Circuit Low Input; P0098 – Intake Air Temperature Sensor 2 Circuit High Input; P0110 – Intake Air Temperature Circuit Malfunction; P0111 – Intake Air Temperature Circuit Range/Performance Problem; P0112 – Intake Air Temperature Circuit Low Input. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.