P0098 Intake Air Temperature (IAT) Sensor 2 Circuit High

P0098 is stored when the engine control module detects a higher-than-expected electrical signal in the Intake Air Temperature (IAT) Sensor 2 circuit.

The word “High” refers to the electrical signal or voltage, not necessarily to the actual temperature of the intake air.

In a commonly used IAT circuit with an NTC thermistor, a high signal voltage generally corresponds to high sensor resistance and therefore a lower calculated air temperature. This is why a vehicle can have P0098 even when the actual intake air is not unusually hot.

The fault can originate from the sensor, wiring, connector, reference circuit, or ECM input.

Understanding IAT Sensor 2

Some engines use more than one intake-air temperature measurement.

IAT Sensor 2 provides an additional temperature reading at a specific point in the intake or charge-air system. Its location varies according to engine design.

It may be installed:

• In the intake duct

• Near the throttle body

• In the charge-air pipe

• Downstream of an intercooler

• In the intake manifold

• As part of a combined pressure and temperature sensor

On turbocharged engines, Sensor 2 is often associated with the charge-air side of the intake system, although the exact arrangement is manufacturer-specific.

Before diagnosing the code, it is therefore important to identify where Sensor 2 is actually located on the particular engine.

Why the ECM monitors intake-air temperature

Air temperature affects air density.

When air becomes colder, it generally becomes denser. When it becomes hotter, its density decreases.

The ECM can use intake-air temperature information to adjust various engine-management functions, including:

• Fuel delivery

• Ignition timing

• Air-fuel mixture

• Boost control

• Emissions strategies

• Engine protection

The precise role of IAT Sensor 2 depends on the engine's calibration.

A faulty signal may therefore affect performance, emissions, or simply trigger a warning light.

How the IAT sensor generates its signal

A common IAT sensor uses an NTC thermistor.

Its resistance changes according to temperature.

Generally:

Temperature decreases → resistance increases

Temperature increases → resistance decreases

The ECM uses a reference voltage and monitors the voltage produced by the sensor circuit.

With a typical voltage-divider arrangement:

Higher resistance → higher signal voltage

Lower resistance → lower signal voltage

Consequently, a high electrical signal can cause the ECM to calculate an unusually low intake-air temperature.

The exact electrical relationship should always be verified using the vehicle's wiring diagram.

What “Circuit High” actually means

P0098 does not mean:

“The intake air is too hot.”

It means:

“The electrical signal detected by the ECM is higher than the expected range.”

This distinction is crucial during diagnosis.

A vehicle could be sitting in warm weather with an entirely normal intake temperature while the ECM receives a high voltage because of an open circuit or another electrical problem.

The code therefore needs to be investigated as an electrical circuit fault.

An open circuit can produce a high signal

One common cause of a high-input condition is an open circuit.

If the sensor circuit is interrupted, the ECM may see a voltage that rises toward its reference voltage, depending on the circuit design.

The ECM can then interpret the signal as an extreme temperature value.

Possible causes include:

• Broken signal wire

• Disconnected sensor

• Loose connector

• Poor terminal contact

• Broken conductor inside the harness

• Damaged sensor

This is why a P0098 diagnosis should begin with the electrical circuit rather than assuming that the sensor is simply measuring high temperature.

The connector deserves close inspection

Inspect the IAT Sensor 2 connector for:

• Disconnected plug

• Corrosion

• Water intrusion

• Bent pins

• Loose terminals

• Poor terminal tension

• Broken locking mechanism

• Damaged wiring near the connector

A connector that is not fully locked can work intermittently.

Vibration from the engine can cause the terminal to lose contact, allowing the signal to rise unexpectedly.

Wiring damage can be hidden

The harness may look intact externally while the conductor inside is broken.

This can happen after years of:

• Engine vibration

• Heat cycling

• Harness movement

• Contact with brackets

• Rubbing against other components

• Previous repairs

If the problem appears intermittently, carefully inspect areas where the wiring bends or moves.

A circuit that works while stationary but fails when the engine moves is a classic example of an intermittent harness problem.

Check the live-data temperature

A scan tool provides a valuable clue.

Look at the temperature reported by IAT Sensor 2.

If the electrical signal is high, the ECM may calculate a temperature that is unrealistically low.

For example, if the engine is operating in warm conditions but IAT Sensor 2 suddenly reports an extremely cold temperature, investigate the circuit.

The exact fallback value varies by vehicle, so there is no single temperature number that proves P0098.

What matters is whether the reading is physically plausible for the current conditions.

Cold-soak testing can be very revealing

If possible, check the sensor reading after the vehicle has been parked for several hours.

Before starting the engine, the intake system should generally be relatively close to the surrounding temperature.

This gives you a useful baseline.

If IAT Sensor 2 reports an extremely cold value while the vehicle has been sitting in warm conditions, the signal is clearly questionable.

Cold-soak testing is particularly useful because it removes many variables associated with turbocharger operation, engine heat and charge-air temperature.

Don't confuse a low calculated temperature with a real cold condition

The sensor may report an extremely low temperature because the electrical circuit is open.

The actual intake air may be perfectly normal.

This is an important diagnostic principle:

The ECM is reacting to an electrical signal, not directly measuring the physical air temperature.

Therefore, an implausible temperature value should prompt an investigation of the signal circuit.

Check sensor resistance

If IAT Sensor 2 uses a conventional thermistor, measure its resistance at a known temperature.

Compare the measurement with the manufacturer's resistance-temperature specification.

If the sensor has an abnormally high resistance compared with the specified value, it may be defective.

However, resistance testing must be performed using the correct specification for that particular sensor.

There is no universal resistance value for all IAT sensors.

A sensor that measures correctly at room temperature can also develop a temperature-dependent problem, so additional testing may be required when the fault is intermittent.

Test the circuit voltage

Once the sensor and connector have been inspected, check the circuit voltage using the manufacturer's wiring diagram.

Determine:

• Reference voltage

• Signal voltage

• Sensor return/ground

• Power supply if applicable

A high signal voltage can help distinguish between a sensor problem and an open or disconnected circuit.

For example, if the signal remains at or near the circuit's reference voltage regardless of temperature, the sensor circuit may be open or the sensor may have extremely high resistance.

The exact expected voltage depends on the vehicle.

Don't assume every IAT circuit is identical

Modern engine-management systems use different electrical designs.

Some sensors are standalone two-wire thermistors.

Others are integrated into multi-function sensors containing:

• IAT

• MAP

• Boost pressure

• Barometric pressure

In an integrated sensor, several circuits may share the same connector.

This makes the manufacturer's wiring diagram especially important.

Testing the wrong terminals or applying voltage to an inappropriate circuit can damage an electronic sensor.

Turbocharged engines add another layer

If IAT Sensor 2 is positioned in the charge-air system, its temperature can change considerably.

During boost, compressed air becomes hotter.

The intercooler then reduces the temperature before the air enters the engine.

Therefore, IAT Sensor 2 can legitimately show substantial temperature changes during acceleration.

However, these changes should correspond with operating conditions.

A sudden transition from a normal intake temperature to an extremely cold value without a physical explanation is much more consistent with an electrical signal problem.

Inspect the sensor installation

Make sure the sensor is:

• Correct for the engine

• Properly installed

• Securely mounted

• Fully connected

• Correctly positioned

If the intake system has been modified, repaired or replaced, verify that the correct sensor is installed in the correct location.

An incorrect sensor can have completely different electrical characteristics and cause an abnormal signal.

Possible symptoms

P0098 may cause:

• Check Engine Light

• Reduced engine performance

• Hesitation

• Poor acceleration

• Changes in fuel consumption

• Incorrect fueling

• Changes in ignition timing

• Reduced boost on some turbocharged engines

• Limp-home operation

• Increased emissions

Some vehicles may show almost no noticeable symptoms.

The ECM may compensate for an unreliable temperature signal by using a substitute value or another calculated temperature.

What can cause P0098?

The most common possibilities include:

• Faulty IAT Sensor 2

• Open signal circuit

• Disconnected sensor

• Broken wiring

• Loose connector terminal

• Corroded connector

• High sensor resistance

• Incorrect sensor

• Poor sensor ground/return

• Reference-circuit problem

• Harness damage

• ECM input fault

The actual cause depends on the circuit design and should be confirmed through testing.

A useful diagnostic sequence

Start by scanning the vehicle and recording all stored, pending and historical codes.

Save the freeze-frame information before clearing anything.

Then examine the IAT Sensor 2 live-data value.

Ask whether the reported temperature makes sense under the current conditions.

Locate the sensor and inspect the connector and wiring.

If the sensor is disconnected or the wiring is visibly damaged, repair that problem first.

If the physical inspection is normal, measure sensor resistance where applicable.

Next, test the signal and reference/return circuits according to the manufacturer's wiring diagram.

Check for an open circuit, excessive resistance and unwanted shorts.

If the circuit tests correctly but the sensor continues to produce an incorrect signal, replace the sensor with the correct specification.

If the sensor and circuit both test correctly, further diagnosis of the ECM input may be necessary.

What if the code disappears after reconnecting the sensor?

That can happen with a loose or poorly seated connector.

However, don't assume the problem is permanently fixed just because the code clears.

Check the connector's terminal tension and locking mechanism.

If the connector was loose, determine why.

A damaged locking tab, stretched terminal or harness strain may cause the same problem to return later.

Intermittent faults require additional attention

Although P0098 describes a high circuit signal, the fault can sometimes appear intermittently.

A partially broken wire may make contact under one condition and lose contact under another.

Temperature can also affect a damaged sensor or connector.

If the code comes and goes, inspect the harness while monitoring the sensor signal and reproduce the operating conditions under which the fault was recorded.

Freeze-frame data can help identify whether the fault occurred:

• During acceleration

• At idle

• During startup

• At a particular temperature

• At high engine load

• After vibration or road movement

Could an intercooler problem cause P0098?

An intercooler can influence the actual intake-air temperature, but it normally does not create a high electrical circuit signal by itself.

If the sensor reports a realistic but elevated temperature during heavy boost, investigate the charge-air cooling system.

If it reports an implausibly low temperature because the electrical signal is stuck high, investigate the sensor circuit.

The distinction between physical temperature and electrical signal is essential here.

Could the ECM be responsible?

An ECM fault is possible but should not be the first conclusion.

Before considering the ECM, verify:

• Correct IAT Sensor 2

• Sensor resistance

• Connector condition

• Wiring continuity

• Signal circuit

• Reference voltage

• Sensor return/ground

• Absence of shorts

• Circuit behavior under operating conditions

Only after these areas have been proven should an internal ECM input problem become a serious possibility.

After the repair

Clear the stored code and monitor IAT Sensor 2 again.

Check the reading during different operating conditions rather than only at idle.

The temperature should remain believable and respond appropriately to changes in:

• Ambient temperature

• Engine load

• Airflow

• Boost pressure

• Vehicle speed

If the original problem was an intermittent wiring fault, test the vehicle under the conditions that previously triggered P0098.

The diagnostic takeaway

P0098 means the ECM has detected a high electrical signal in the IAT Sensor 2 circuit.

It does not mean that the intake air itself is necessarily too hot. In a typical NTC-based system, a high signal can correspond to an extremely low calculated intake temperature, particularly when the circuit is open or the sensor has abnormally high resistance.

The most effective diagnosis begins with the live-data temperature reading and then moves through the sensor, connector, wiring, reference and return circuits.

The objective is to determine why the ECM is receiving an abnormally high signal—whether the cause is an open circuit, faulty sensor, poor connection, wiring problem, or ECM input fault.